nd

V. Molina a,b,, C. Montes c, P. Tamayo d, R. Villa a, M. Isabel Osuna e, J. Prez a, C. Sancho b,f,ardo

a Department of Psychiatry, Hospital Clnico Universitariob Institute for Neuroscience of Castilla y Len, Universidadc Department of Medical Physics, Hospital Clnico Universd Department of Nuclear Medicine Hospital Clnico Univee Department of Psychiatry, Hospital Reina Sofa, Crdobaf Department of Physiology and Pharmacology, Universidag Department of Neurology, Hospital Clnico Universitario

Results: In comparison with normal subjects, the patients exhibited lower PPI, although the difference was

Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 5361

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Progress in Neuro-PsychopPsychi

j ourna l homepage: www.e lnot statistically signicant. Perfusion was signicantly lower in the prefrontal and premotor regions of thepatients. In the patient group, a statistically signicant difference was observed between PPI and perfusion inthe parietal, premotor, and cingulate regions. When the associations were analyzed in the RO patients alone,a positive correlation was also found between prefrontal perfusion and PPI, while anterior hippocampalperfusion was inversely related to PPI.Conclusions: These results support the notion that decient sensory-motor ltering is associated withdecreased cortical task-related activation in schizophrenia.

2008 Elsevier Inc. All rights reserved.

1. Introduction

Brain activity patterns as measured with positron emissiontomography (PET) or single photon-emission tomography (SPECT)are consistently different between schizophrenia patients and healthy

controls (Hill et al., 2004). This difference is usually reported as adecreased activation of the regions involved in the performance of atask, and can be found in different regions and conditions. Forexample, hypoperfusion and hypometabolism have frequently beendescribed in the prefrontal (PF) areas associated with cognitiveactivation (Andreasen et al., 1992), as well as in visual areas in theAbbreviations: dB, decibels; DLPF, dorsolateral prefmaximum; MBq, microbecquerels, ms, milliseconds; ROand negative symptoms scale; PET, positron emission toprepulse inhibition; SD, standard deviation; SPECT, singized tomography; SPM, statistical parametric mapphexamethylene-propylenaminoxime. Corresponding author. Department of Psychiatry, H

Paseo de San Vicente, 58-182, 37007 Salamanca, Spain.E-mail address: vmolina@usal.es (V. Molina).

0278-5846/$ see front matter 2008 Elsevier Inc. Aldoi:10.1016/j.pnpbp.2008.10.011patients (6 with recent onset, RO) and 16 control subjects. These measurements were compared betweenpatients and controls and the correlation between PPI and perfusion was evaluated within each group, usingStatistical Parametric Mapping.SchizophreniaPerfusionPrepulse inhibition(assessed with single phota r t i c l e i n f o

Article history:Received 29 April 2008Received in revised form 23 September 2008Accepted 9 October 2008Available online 30 October 2008

Keywords:, Salamanca, Spainde Salamanca, Salamanca, Spain

itario, Salamanca, Spainrsitario, Salamanca, Spain, Spaind de Salamanca, Salamanca, Spain, Salamanca, Spain

a b s t r a c t

Background: Processes underlying cortical hypoactivation in schizophrenia are poorly understood but someevidence suggests that a decient sensory ltering is associated with the condition. This ltering decit canbe studied by using measures of prepulse inhibition (PPI) of the startle reex.Objective: To evaluate the contribution of sensory ltering decits to cortical hypoperfusion during anattention test in schizophrenia.Method: Measurements of PPI of the startle reex and perfusion during the performance of a Stroop test

on emission tomography) were obtained in 10 acutely treated schizophreniaT. Lpez- Albuquerque g, A. C so b, O. Castellano b, D.E. Lpez bA pilot studyCorrelation between prepulse inhibition atest in schizophreniarontal; FWHM, full-width half, recent onset; PANSS, positivemography; PF, prefrontal; PPI,le photon emission computer-ing; Tc-HMPAO, technetium

ospital Clnico de Salamanca,Fax: +34 923 291448.

l rights reserved.cortical perfusion during an attentional

harmacology & Biologicalatrysev ie r.com/ locate /pnpbpresting condition (Andreasen et al., 1997; Desco et al., 2003). However,hyperactive patterns may be also found, mainly in the limbic areas(Molina et al., 2005).

The processes underlying such abnormal activation are still poorlyunderstood. One of the possible contributing causes is decientsensory ltering, which could hinder task-related activation. Indeed,there is support for such a gating deciency in schizophrenia, sincethalamic histology, volume and metabolism may be altered in this

The healthy controls had no personal or familial psychiatricantecedents. Tomatch themwith the patient group, it was ascertainedthat none of the subjects had a college-level education, and effortswere also made to match the parental school years. No differences inage or parental socioeconomic status (SES) as dened by Hollingsheadand Frederick (1953) were observed between the patient and controlgroups (Table 1). There were no signicant differences in parentaleducational level between patients and controls.

The exclusion criteria for patients and controls were: any axis Idiagnosis other than schizophrenia for the patients or any axis Idiagnosis for the controls; any neurological illness, a history of cranialtrauma with loss of consciousness, past substance dependence,excluding nicotine or caffeine; drug abuse during the previous3 months (current consumption being ruled out by urinalysis);signicant hearing loss and any current treatment with known actionson the central nervous system. None of the patients or controls hadreceivedmood-stabilizers, antidepressants, or depot neuroleptics overthe 6 months preceding the study. All patients and controls under-went a cautionary MRI scan to exclude any abnormality of neurolo-gical relevance as judged by an expert radiologist. Prior to PPI testing,audiometric screening excluded individuals with a hearing impair-ment in both the patient and control groups (threshold N40 dB (A) at1000 Hz).

After the subjects had been given detailed information about thestudy, written informed consent was obtained from each of them andfrom a rst-degree relative. The research and ethics boards of the

54 V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 5361illness (Andreasen et al., 1994; Buchsbaum et al., 1996; Thune andPakkenberg, 2000), and sensory ltering is one of the key thalamicfunctions (Steriade et al., 1997).

Prepulse modulation of the auditory startle reex (ASR) can beused to measure sensory-motor gating (Geyer and Braff, 1987). ASR isincreasingly used as a measurement of the plasticity and changes thatoccur during the processing of sensory-motor information (Koch andSchnitzler, 1997). The prepulse inhibition (PPI) of ASR represents anoperational measure of information-protective pre-attentionalmechanisms. PPI is the normal inhibition of a startle response to anintense, abrupt stimulus when it is preceded by a weak prepulse.Over the past decades, many studies have reported lower PPI values inschizophrenia (Geyer et al., 2001).

Sensory gating is a process that occurs earlier than corticalactivation, and hence it seems reasonable to propose that decits inthis process might contribute to cortical hypoactivation in schizo-phrenia. It therefore seems worthwhile to evaluate whether themeasurement of sensory ltering is correlated with cortical hypoacti-vation in schizophrenia. At least one research group has reported acorrelation between gating decits and cortical hypoactivation in thatillness (Kumari et al., 2003). However, cortical decits may, in turn,contribute to a decrease in PPI in schizophrenia (Hazlett et al., 1998).

An association between PPI and cortical activation is alsosuggested by the observation that greater PPI is related to superiorabilities in strategy formation and execution times (Bitsios et al.,2006), as well as to better efciency in an attention task (Giakoumakiet al., 2006). Recent results also suggest an association betweensensorimotor gating andworkingmemory performance (Csomor et al,2008).

Accordingly, if sensory-motor gating and cortical activation decitsare associated a relationship would be expected between thepercentage of PPI and perfusion in the areas involved in the taskwhere cortical activity is being studied. Evaluation of this possibilitywould require an assessment in the same individuals of thepercentage of PPI and perfusion or metabolism during a cognitivetask. To accomplish this, in the present work we evaluated a group ofacutely treated schizophrenia patients with both PPI and perfusionSPECT scans obtained during a Stroop test, which is expected toactivate the frontal and cingulate regions (Bush et al., 1998; Pardoet al., 1990). On performing the three parts of the Stroop task, subjectsmust successively read colour names written in black, to namecolours, and to name the ink colour inwhich a discrepant colour nameis written.

2. Patients and methods

2.1. Subjects

Our sample included 10 acutely treated patients (6 males)diagnosed with paranoid schizophrenia by consensus between twopsychiatrists (VM, who was the treating clinician in all cases, and RV,JP, or MO). For all of these patients, both PPI and SPECT data wereavailable. Moreover, 16 controls (7 males) were included. Amongthem, 9 (4 males) had both PPI and SPECT and 7 (3 males) had only PPIdata available. Patient diagnosis was conrmed using the StructuredClinical Interview for Diagnostic and Statistical Manual (SCID, patients'version) and data obtained from clinical interviews, together withinformation from the patients' families and the clinical staff. Allpatients were in a short-term psychiatric unit for the treatment ofpsychotic symptoms. The Positive and Negative Syndrome Scale (Kayet al., 1987) was used to evaluate symptoms (Table 1).

Prior to their inclusion, 6 patients were neuroleptic-nave (NN),and 4 were neuroleptic-free since they had quit their medication formore than 1 month. In all cases, a short treatment with haloperidol(5 mg/d) was given immediately after their admission to the

psychiatric ward. The duration of this treatment was between 24and 36 h, although it was withdrawn during the 12 h prior to SPECTand PPI. Thus, the patients in our sample cannot be properlyconsidered as NN or neuroleptic-free at the time of the perfusionand PPI exams, but rather should be considered minimally-treatedpatients, and we shall henceforth refer to these as recent onset (RO)patients.

Both data modes were acquired on the same or consecutive daysin the patients and on the same day in the controls. Benzodiaze-pines were allowed for insomnia (Lorazepam 2.5 mg) and 5patients received this drug. After the PPI and SPECT examinationshad been performed, most patients received risperidone as theironly drug.

Table 1Demographic and cognitive data of patients and controls

Patients

RO patients(n=6)

All patients(n=10)

Controls withPPI and SPECT(n=9)

Controls withPPI(n=16)

Age 28.74 (8.61) 32.96 (7.46) 30.01 (9.24) 27.33 (8.65)Male:female ratio 4:2 6:4 4:5 7:9School years 12.17 (4.73) 10.92 (4.89) 13.19 (3.60) 14.11 (4.08)Parental SES 1.41 (0.61) 1.79 (0.91) 1.81 (1.09) 1.90 (1.02)Illness duration (years) 0.91 (0.79) 4.23 (3.15)PANSS-positive 29.40 (3.59) 30.82 (3.70)PANSS-negative 26.00 (10.19) 25.90 (9.63)PANSS total 103.17 (19.21) 104.20 (19.88)Stroop performance(colour-incongruentcondition)

20.11 (9.22) 22.09 (8.27) 31.67 (8.03) 34.01 (9.17)

Stroop (word-readingcondition)

75.28 (13.09) 79.36 (15.01) 89.16 (10.78) 88.70 (10.18)

Stroop performancewas dened as the number of correct responses in 45 s in theword-colour incongruent condition.RO: recent onset; SES: socioeconomic status, according to the Hollingshead andFrederick scale (see text).Values are represented as means (SD). Signicant difference between patients (n=10) and controls (n=16); (U=21, z=2.13,

p=0.03; MannWhitney U test).participating institutions endorsed the study.

55V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 53612.2. Scanning procedure

The SPECT procedure was performed in patients and controls withthe same scanner, following identical protocols. All subjects per-formed a Stroop test paradigm between 10 min before and 10 minafter a bolus intravenous injection of 740 MBq of 99mTc-HMPAO, andscans were obtained 2030 min after the injection. For SPECTacquisition, we used a dual-head rotating gamma camera (Axis,Picker) tted with a fan-beam collimator. SPECT data were acquiredover 25 min in step-and-shoot mode (120 steps, 3 steps, 25 s/step)using a symmetric window of 20% centred around 140 keV and a128128 matrix. Images were reconstructed with an iterative methodusing a low-frequency pre-lter (order 5; cut-off 0.40 cm1) and werecorrected for attenuation (Chang 0.09/cm). Sixty-four transaxial sliceswere obtained. The SPECT study was performed after a fasting periodof more than 6 h. Coffee and psychoactive beverages were prohibited.

2.3. Cognitive assessment

The Stroop test is an attention task aimed at evaluating theattentional capacity of subjects, and in particular their resistance tointerference, since in it they must name the colour of the ink in whichthe name of a different colour is written.We used the standard versionof this test, with the presentation of 100 stimuli of each part (word-reading, colour and incongruent word-colour). The subjects wereinstructed to perform the three parts successively several times, untilHMPAO uptake could be considered complete (20 min after itsinjection), with a short resting period of 1 min between thecompletion of each repetition (i.e., of each of the three parts of thetest). Performance was dened as the number of correct responses in45 s in the word-colour incongruent condition in the rst completion.

2.4. PPI acquisition and processing

The acoustic startle test session aimed at measuring PPI consistedof several parts, with a total acquisition time of about 1520 min.During the session, the subjects were sitting comfortably in a double-walled, sound-attenuated and slightly dark chamber. Ambient roomnoise was measured using an ear coupler on the headphones.

First, the recording electrodes were placed on the orbicularis andmassetermuscles of the subjects. The subjectswere thenasked to remainrelaxed, with their eyes open. After emplacement of the electrodes, a5 min acclimatising period began, with the cabin already closed. Duringthis period, a background, white noise of 60 dB was present, which wasalso maintained for the rest of the session. The test itself consisted of 5blocks of 2 different trials: pulse alone (105 dB, 50 ms bursts of whitenoise), and acoustic startle stimuli preceded 50 ms by a prestimulus(75 dB, 20 ms bursts of white noise, stimulus onset-asynchrony 70 ms).The trials were presented binaurally through headphones (DR-531B-14;Nihon Kohden America, Inc., USA). The sessions began and ended with ablock of three startle stimuli (pulse alone). Between these two blocks,there were three blocks of 3 prepulsepulse and 1 pulse-alone trial,presented in a pseudo-randomorder. Themean inter-trial intervalswereof 15 s and the interval between blocks was 120150 s.

EMG recordings of the orbicularis and masseter muscles weretaken with a Neuropack Kohden electromyograph (Nihon Kohden).The bin-width for the electromyographic response was 300 ms,including 50 ms of basal activity and the 100 ms following theresponse, and was bandpass-ltered (11000 Hz).

The startle responses were averaged for each subject (response topulse alone) and were used as data for the statistical analyses. All theresults from the startle and PPI tests are reported as meansSD. Theresults of the PPI are reported as % PPI, calculated according to thefollowing formula:

% PPI=100 [(magnitude of pulse alonemagnitude of prepulse

pulse)/magnitude of pulse alone]Given the small number of subjects, in order to reduce the numberof comparisons we selected only the percentage of attenuation of theamplitude of the startle reex response (% PPI) in the orbicularismuscle as the variable to be assessed as an index of the sensory-motorgating process. Other data obtained in the study, such as the acousticstartle response (amplitude and latency), are not directly related topre-attentional or attentional processes, and were therefore notanalyzed in depth.

During at least the 3 h preceding PPI, neither the patients nor thecontrols smoked, because the former had been admitted to thehospital and the latter were also in hospital to undergo their SPECTscans. Thus, the smoking abstinence period of the patients was longerthan 24 h in all cases.

2.5. Image analysis

SPECT images were analyzed with the SPM5 software package(from the Welcome Dept. of Cognitive Neurology, London, UK)(Frackowiak et al., 1997). Studies were transformed into a Talairachstereotactic space (Talairach and Tournoux, 1988), warping each scanto a reference template that already conformed to the standard space.Images were reformatted to a nal voxel size of 222 mm andsmoothed using an isotropic Gaussian kernel of 121212 mmFWHM. The grey-level threshold was set to 0.8; i.e., only voxels withan intensity level above 0.8 of the mean level for that scan wereincluded in the statistical analysis. Intensity normalizationwas carriedout using proportional scaling, hence assuming that global brainmetabolism was equal for each scan.

2.6. Statistical methods

The normality of the distribution of the variables was examinedusing the KolmogorovSmirnoff test, and when it could not beassumed non-parametric tests were used.

Performance in the Stroop test (number of correct responses in 45 sin the word-incongruent condition) was compared between patientsand controls with a MannWhitney U test.

The signicance of the differences in %PPI and the startle responsebetween patients and controls was assessed using the MannWhitneyU test. We repeated the comparison between patients and the 16controls with the available PPI data. In light of the differences in sexdistribution between the patients and controls, we had planned apriori to corroborate that the same pattern of differences would bepresent between male controls (n=7) and male patients (n=6).

In order to assess the clinical relevance of the PPI measurements,we calculated the correlation coefcients between positive, negative,and total symptoms scores in the PANSS and PPI using Spearman's rho.With the same aim, we also calculated correlation coefcientsbetween the Stroop performance and PPI.

Following this, Statistical Parametric Mapping (SPM-5) was used toassess perfusion differences between the patients and controls. Agewas included as a covariate in this model.

SPM was then used to evaluate the correlation between PPI andperfusion across the brain. Correlations were calculated on a voxel-by-voxel basis, using the multiple regression design incorporated in theSPM. These calculations were carried out separately in patients andcontrols. In a second step, the calculations were repeated using theStroop performance as a covariate. Moreover, we repeated thesecalculations using only the data in the RO group to conrm that if anyassociation was found it was not simply due to a residual effect of theprevious treatment in the chronic patients.

For all SPM analyses, the one-tailed signicance threshold was setat pb .001, uncorrected with a minimum extent of 50 voxels, except forthe post-hoc analyses in the RO group. In this case, owing to thelimitation of the number of subjects we considered the results

signicant at pb .0025 and more than 50 voxels.

3. Results

3.1. Comparisons between groups

3.1.1. Sex distributionAlthough there were more males in the patient group, sex

distribution was not statistically signicant with respect to the 9controls with PPI and SPECT available (2=2.55, df=2, p=0.12) norwith respect to the 16 controls with PPI alone (2=1.70, df=2, p=0.18).

3.1.2. Cognitive performanceThe patients performed well in the word-reading condition of the

Stroop test, but their performance was signicantly poorer than thatof the controls in the word-incongruent condition (Table 1).

In the patients, PPI was correlated with perfusion in the upper

Table 3Perfusion differences between the patients (n=10) and controls (n=9) with PPI andSPECT data available (pb0.001, regions greater than 50 voxels, uncorrected)

Local maxima coordinates z Voxel extent

Regions with higher activity in controlsRight dorsolateral 50, 18, 38 4.49 415Right premotor 32, 6, 54 3.94 133Left premotor 14, 4, 70 3.78 272

Regions with higher activity in patientsCerebellum 0, 50, 22 3.90 55Left orbitofrontal 28, 48, 6 3.82 51

Differences still signicant in the RO patients (n=6) as compared to controls (n=9),at pb0.0025.

Controls

Controls with PPI and SPECT(n=9)

Controls with PPI(n=16)

60.09 (26.67) 56.70 (29.51)59.30 (27.1) U=31.00, z=1.14, p=0.27 56.89 (26.9) U=59.00, z=1.10, p=0.28591.78 (860.12) 529.33 (692.01)732.51 (744.21) U=22.00, z=2.09, p=0.03 653.79 (737.22) U=51.00, z=1.89, p=0.07

5 dB pulse alone in patients and controls (both the whole group and the RO subgroup) andbetween the whole group of patients and, respectively, the whole group of controls and the

56 V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 53613.1.3. Effect of prepulse on startle responseThe startle response amplitude on the orbicularis muscle was

lower in the patients in comparison with the controls with PPI andSPECT done and, at trend level, in comparison with all the controlswith available PPI data (Table 2).

The PPI value was lower in patients, but the difference did notreach statistical signicance (Table 2). This was also the case of thecomparisons between the patients and the 16 controls with PPI dataavailable (Table 2).The same pattern was also found in a comparisonbetween the 7 male controls (PPI mean 64.1223.34) and the 6 malepatients (PPI mean 48.0128.60, U=17.00, z= .95, p=0.38) withavailable PPI data. We repeated these comparisons using parametricmethods (Student's t) and the differences between patients andcontrols were again not statistically signicant.

3.1.4. PerfusionThe schizophrenia patients showed lower perfusion values than

the controls (pb0.001) in both the right and left premotor and rightdorsolateral (DLPF) regions. In the patients, smaller areas ofhyperactivity were detected in the cerebellar vermis and left inferiorPF regions (Table 3; Fig. 1). The same pattern was identied atpb0.0025 when the RO patients were compared with the healthycontrols (Fig. 1).

3.2. Correlation between PPI and clinical and cognitive scores

In the patients, the PPI values were signicantly related to negativesymptom scores (rho=0.86, pb0.01) and total symptom scores(rho=0.88, pb0.01). There was no signicant correlation betweenPPI and Stroop performance (rho=0.43, pN0.10).

3.3. Correlation between perfusion and PPI measures

In the controls, PPI was positively correlated with perfusion in theupper parietal and occipital regions (Table 4; Fig. 2).

Table 2Mean values of the % of PPI (prepulse 75 dB)

Patients

RO patients(n=6)

All patients(n=10)

PPI values (%), masseter 48.78 (29.56) 40.55 (30.11)PPI values (%), orbicularis 40.01 (27.45) 43.24 (28.27)Amplitude of the startle response (V), masseter 226.12 (149.33) 219.42 (128.56)Amplitude of the startle response (V), orbicularis 295.20 (102.17) 256.01 (122.78)

Prepulse inhibition values and of the response startle amplitude (V) obtained with a 10controls, in the orbicularis occuli and masseter muscles. The statistics of the comparisonssubgroup of controls with PPI and SPECT done are shown. pb0.05.right parietal lobe (Table 4; Fig. 2), similarly to the controls. Moreover,in the patients PPI was also directly correlated with perfusion in themiddle cingulate and left premotor regions (Fig. 2). This pattern ofcorrelation was the same when the Stroop performance wasintroduced as a covariate.

3.3.1. Correlations in the RO patientsWhen this correlationwas evaluated in the RO patients alone (n=6),

a positive correlation was also found between PPI and perfusion in theright parietal and left premotor regions (pb0.0025, Table 4; Fig. 2).Moreover, in this subgroup a signicant negative correlation was alsofound between perfusion in the anterior hippocampal region (coordi-nates 32, 8, 18, voxel extent=389) and PPI (Fig. 3).

When Stroop performance was introduced as a covariate, the samecorrelationpatternwas found in the premotor and limbic areas of theROpatients. Moreover, additional positive correlations emerged in the ROgroup between PPI and perfusion in the medial prefrontal (coordinates2, 48, 48, voxel extent=102, z=4.85), right DLPF(coordinates 24, 34, 52,voxel extent=84, z=3.92) and right orbitofrontal (coordinates 28, 38,20, voxel extent=237, z=4.51) regions (Fig. 4).

4. Discussion

In this work, the schizophrenia patients showed a signicantcorrelation between the percentage of attenuation due to prepulse ofthe startle reex (i.e., PPI) and perfusionmeasured during a Stroop testin regions known to be activated by this task (middle cingulate andparietal, and in the RO patients prefrontal, after including perfor-mance as a covariate). The patients showed the usual hypofrontalpattern, their collaboration in the task presumably being normal, inlight of their performance data.

Previous neuroimaging results have shown that the Stroop testactivates the middle frontal and anterior cingulate (Bush et al., 1998;Pardo et al., 1990), motor and premotor (Bush et al., 1998; Petersonet al., 1999), as well as the parietal (Brown et al., 1999; Bush et al.,

connd r

57V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 53611998; Leung et al., 2000) regions. The percentage of PPI in our patients,and also in the controls, was directly associated with the perfusionvalues in these areas. Thus, our data are consistent with the hypothesisthat some factors underlying the usually lower PPI in schizophrenia,such as a sensory ltering decit (Braff and Geyer, 1990; Geyer andBraff, 1987), might interfere with task-related cortical activation in theillness.

In the complete group of patients and in the RO subgroup, a lowerPPI was found as compared to the control subjects, although thisdifference did not reach statistical signicance. Our patients showed adecreased startle response as compared to controls, which might havecontributed to the observed lack of statistical signicance in thedecrease in PPI with respect to controls, although at least one other

Fig. 1. Top. Regions with signicantly lower perfusion in patients (n=10) as compared to(n=6) as compared to controls (n=9, pb .0025). In both cases, left and right premotor agroup has reported a signicant decrease in PPI in schizophrenia,along with a decreased startle response (Quednow et al., 2006).Moreover, the magnitude of the PPI differences found in the presentstudy between the patients and controls (roughly one third less in thepatients than in the controls) is similar to the baseline magnitudereported in other studies, despite the differences in the methods usedto elicit PPI (Quednow et al., 2006), and it lies within the rangedescribed in studies of patients treated with olanzapine, risperidone,or haloperidol (Wynn et al., 2007). For example, values of 68.522.0 ofPPI in controls and 32.148.3 have been reported in patients (Kumariet al., 2003). Thus, it may be assumed that the lack of a signicantdifference in PPI between our patients and the controls may have beendue to the small sample size.

However, the lack of signicant differences in PPI may also havebeen due to factors that increased the variance in the patients; notablynicotine consumption or the treatment received previously. The lattercan reasonably be discarded since the pattern was very similar in theRO subjects. As regards nicotine, its effects may be related to acuteconsumption (Duncan et al., 2001; Postma et al., 2006) or abstinence.The acute effects of nicotine on PPI were probably minimal in oursubjects since none of them smoked during the hours prior to thestudy of PPI. In turn, abstinence would decrease PPI in schizophrenia(George et al., 2006), and therefore would not account for the lack of asignicant decrease in PPI in our patients. Nevertheless, an effect ofnicotine withdrawal on the degree of PPI reduction in our subjectscannot be discarded, since it has been reported that healthy controlsscoring high on a scale measuring tolerance to nicotine withdrawalshow signicantly less PPI than those who score low on that scale(Kumari and Gray,1999). Moreover, differences in themethods used toelicit PPI may also be related to the lack of signicant differences in PPIbetween patients and controls. For example, there are differences inthe level of background noise (60 dB in our study, as opposed to 70 dBused by most laboratories whose studies have reported a signicantdecrease in PPI). The results obtained for one group withoutbackground noise failed to reveal a PPI decit in schizophreniapatients (Wynn et al., 2007). Nevertheless, using a background noiseof 60 dB, at least one group found decreased PPI in schizophrenia andcannabis users during one of two conditions in which PPI wasdetermined in their study (Kedzior and Martin-Iverson, 2007).

Finally, another factor contributing to the lack of a signicantly

trols (n=9) (pb .001). Bottom. Regions with signicantly lower perfusion in RO patientsight DLPF areas were hypoactive.reduced PPI in our cases is related to the attentional modulation of PPI.PPI is more robust when attending to than ignoring the prepulse, andseveral groups have reported that the attentional modulation of PPI isalso impaired in schizophrenia and schizotypal patients (Dawson et al,2000; Hazlett et al, 2007). Thus, it is conceivable that using an activeparadigm tomeasure PPI, our patients could have shown a statisticallysignicant reduction in PPI. However, using passive paradigms such asthe one used here other groups have detected reduced PPI inschizophrenia (Geyer et al., 2001).

Table 4Correlations between PPI measured on orbicularis muscle and perfusion during a Strooptest (pb0.001, extent greater than 50 voxels) in patients and controls

Local maxima coordinates z Voxel extent

Patients: direct correlationsRight parietal 44, 50, 60 4.08 84Left premotor 40, 16, 68 4.05 60Middle cingulate 0, 6, 44 3.99 84Left premotor 38, 14, 46 3.51 79

Controls: direct correlationsRight parietal 18, 68, 44 4.56 68Left occipital 14, 54, 16 3.96 79Left posterior temporal 48, 54, 10 3.64 54

No inverse associations were detected. Correlations in the patients still signicant in the RO subgroup at pb0.0025.

58 V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 5361Our patients received a minimum treatment prior to the PPI andSPECT studies. This was done to avoid the bias due to the inclusiononly of patients able to cooperate in imaging procedures. Dopamine

Fig. 2. Top (rows 1 and 2). Regions with a signicant correlation between PPI (orbitalis muscupper parietal and occipital regions were positively associated with PPI in this group. Middleperfusion during the Stroop test in the patients, n=10 (pb .001). Perfusion in the right upperwith a signicant correlation between PPI (orbitalis muscle) and perfusion during the Strooppositively correlated with PPI in this group.function may inuence PPI (Geyer et al., 2001), and in schizophreniaimportant differences in dopamine transmission can be expectedbetween acute and remission states (Laruelle et al., 1999). It therefore

le) and perfusion during the Stroop test in the controls, n=9 (pb .001). Perfusions in the(rows 3 to 5). Regions with a signicant correlation between PPI (orbitalis muscle) and

parietal regionwas positively associated with PPI in this group. Bottom (row 6): Regionstest in the RO patients, n=6 (pb .0025) Perfusion in the right upper parietal region was

seems necessary to study acute psychotic patients, although this maybe unfeasible in most cases in which they have not undergone anyprevious treatment. The minimum treatment with haloperidol thatour patients received prior to SPECT may have inuenced their brainperfusion patterns, since with PET a decrease in frontal metabolismhas been reported after long-term treatments (Holcomb et al., 1996).Regarding the acute administration of haloperidol to drug-freeschizophrenia patients, as used here, awidespreadmetabolic decreasehas been found 12 h after its administration in patients that did notrespond to the drug, but not in those who did respond (Bartlett et al.,1998). Since there is no reason to assume that the patients in our studywould not have responded to haloperidol, this would suggest only aweak effect on perfusion of the acute haloperidol doses administeredto our patients. This is also supported by the similar pattern ofhypofrontality described in NN patients under activation conditionssimilar to those used here (Andreasen et al., 1992; Buchsbaum et al.,1992). Thus, the effect of haloperidol may not be the only reason forthe hypofrontality observed in our patients as compared to controls.

does not modify PPI measurements, even after prolonged use,previous minimal treatment with this drug is unlikely to account forthe association found here between cortical activation and sensory-motor gating.

Three studies from the same group have evaluated cerebral activitycorrelates during a PPI paradigm in unmedicated chronic schizophreniapatients and controls, using PET to assess cortical metabolism. Althoughthis is a different approach to the one used here, the results of thesestudies point to the activation of frontal regions during PPI in thecontrols but not in the patients (Hazlett and Buchsbaum, 2001; Hazlettet al., 1998). In a more recent report, schizophrenia patients showed areduced activation of the prefrontal, caudate and thalamic regionsduring the attentive PPI condition in comparison to controls (Hazlettet al, 2008). This is coherent with the direct correlation observed in ourpatients between frontal and cingulate perfusion and PPI and the lowerperfusion seen in the patients as compared to the controls. Takentogether, these data indicate that lowPPImay be correlatedwith a lowerdegree of frontal activation in schizophrenia patients than in controls. If

Fig. 3. Regions with a signicant inverse correlation between PPI (orbitalis muscle) and perfusion during the Stroop test in the RO patients (n=6, pb .0025). Inverse correlations werefound between the perfusion in the hippocampus and PPI in this group.

59V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 5361Moreover, since the available data support the notion that haloperidolFig. 4. Regions with a direct correlation between PPI and perfusion in the RO patients aftercorrelations. Medial frontal, right DLPF and right orbitofrontal perfusion directly correlateda decit in sensory gating in schizophrenia is assumed, this would alsoincluding Stroop performance as a covariate in addition to the above-described directwith PPI.

60 V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 5361be coherent with decreased frontal activation under cognitive para-digms inpatientswith lower PPI. Those authors (Hazlett et al.,1998) alsodescribed a positive correlation in their patients betweenmetabolism inprefrontal area 10 and PPI, equivalent to the correlation betweenorbitofrontal perfusion and PPI in our RO patients, Another groupevaluated the association between perfusion as measured by fMRI andtactile PPI in controls and schizophrenia subjects treated with conven-tional antipsychotics (Kumari et al., 2003). They found a lower degree ofPPI in the patients, accompanied by a blunted haemodynamic responseduring the PPI task, in a complex set of regions encompassing frontal,parietal, occipital, striatal, limbic and cerebellar locations. These resultsare not easily comparable to ours, given the relevant changes thatclassical antipsychotics exert on many of these regions, in particular thebasal ganglia (Buchsbaum et al., 1987; DeLisi et al., 1985). However, theyare consistentwith the notionof the existence of anassociationbetweenPPI and cortical activation decits in schizophrenia.

Nevertheless, we cannot adequately identify the direction of thatassociation; i.e., we cannot state whether cortical dysfunction produces adecit in PPI or whether sensory gating decits produce a ooding of thecortex that impairs its activation. Sensory gating is an early process andthus may be primary, but hypofrontality might also contribute to thedecrease in PPI in schizophrenia (Hazlett et al., 1998). Preclinical data alsoshow that the frontal depletion of dopamine impairs PPI in the rat (Bubserand Koch,1994), which could indicate the primary role of cortical decits.

We found an inverse correlation in the RO patients between limbicperfusion and PPI: the greater the limbic perfusion, the lower the PPI.Limbic hyperactivation has been described in schizophrenia patientsand has been related to prefrontal atrophy (Molina et al., 2005),positive symptoms (Liddle et al., 1992; Molina et al., 2005), andcognitive performance (Heckers et al., 1998). Together with thecorrelation between PPI and low cortical activation, the associationbetween PPI and limbic hyperactivity supports the hypothesis thatsensory ltering decits may contribute to a disorganized activationacross the brain, as proposed for schizophrenia (Manoach, 2003). Suchan association was only detected in the RO patients, which suggeststhe cancellation of such a correlation in treated patients.

Our study has several limitations; notably, the number of subjects.This implies that the results can only be considered preliminary.Another limitation is the different number of males and females in thepatient and control groups. Even within the same female subjects,changes along the menstrual cycle may inuence PPI values(Swerdlow et al., 1997). However, PPI decits in schizophrenia arenot restricted to males (Braff et al., 2005). In this latter study, femalepatients and controls showed a similar pattern of differences at 54 dBprepulse intensity (stimulus onset-asynchrony 30 and 120 ms) to thatfound in the present one. Moreover, when we compared the malepatients and the male controls, the differences remained the same aswhen the whole group was considered. Another limitation is relatedto the state of acute psychosis of the patients, which could determine alower degree of collaboration. However, the patients' performance onthe Stroop test was good, as evidenced in the reading condition,suggesting that in our cases acute psychosis was not associated withpoor collaboration in the test. Finally, we did not simultaneouslycollect PPI and perfusion data. The future use of functional MRI mayhelp to overcome this problem, since it would allow a simultaneousassessment of these parameters to be made, perhaps also during theperformance of an attention task.

In conclusion, sensory-motor gating measured with PPI andcortical perfusion in some regions as measured with SPECT may bepositively correlated in schizophrenia.

Acknowledgements

Supported in part by a Grant from the Fondo de InvestigacionesSanitarias (PI 040025), from the Spanish Ministry of Health and by the

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61V. Molina et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 33 (2009) 5361

Correlation between prepulse inhibition and cortical perfusion during an attentional test in sc.....IntroductionPatients and methodsSubjectsScanning procedureCognitive assessmentPPI acquisition and processingImage analysisStatistical methods

ResultsComparisons between groupsSex distributionCognitive performanceEffect of prepulse on startle responsePerfusion

Correlation between PPI and clinical and cognitive scoresCorrelation between perfusion and PPI measuresCorrelations in the RO patients

DiscussionAcknowledgementsReferences