Iconic memory loss linked to onset of Alzheimer's disease
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Newsdesk 144 http://neurology.thelancet.com Vol 4 March 2005 Cortical excitability can be facilitated or suppressed for over 1 h by certain patterns of short duration, repetitive transcranial magnetic stimulation (TMS). Researchers from the Institute of Neurology at University College London (UK) found that low intensity pulses of TMS at 50 Hz for a short duration have a long-lasting after effect on the motor cortex in healthy people (Neuron 2005; 45: 201–06). Hugo Théoret (Université de Montréal, Canada) believes “the discovery of an efficient, short, and safe method of modulating cortical excitability is a great advance that will likely impact cognitive research and therapeutic opportunities”. Previous attempts to affect the plasticity of people’s brains with repetitive TMS have had limited success; the after effect was generally weak and variable, and the longest after effect produced (lasting about 30 min) required TMS of the same duration. The UCL research group applied the theta burst paradigm—a method of stimulation that has produced long-lasting effects in brain slices after short periods of stimulation—to the motor cortex of nine healthy adults. John Rothwell, one of the researchers, explained, “the theta burst paradigm is a way of spacing out the repetitive TMS pulses so that TMS application is short yet the effect is long and controllable”. Before and after the researchers delivered the sequence of TMS bursts to the hand area of the motor cortex, they gave a single pulse of TMS to measure the motor evoked potential at the right first dorsal interosseous muscle of the New era of transcranial magnetic stimulation The decline of iconic memory may be a key to the early detection of Alzheimer’s disease (AD). Elderly people with mild cognitive impairment (MCI)— who commonly develop AD—showed marked deficiencies in iconic memory, according to a recent study. Iconic memory is a very brief snapshot of a visual stimulus, and lasts about 300–500 ms before fading. Lead author Zhong-Lin Lu (University of Southern California, CA, USA) first became aware of the potential link between shortened iconic memory and AD several years ago when studying iconic memory among a group of volunteers. A healthy 58 year old man, who was not suffering from any type of cognitive decline and who was employed in a very high-profile job, puzzled the researchers by his lack of iconic memory. 2 years later he was no longer able to do his job because of memory decline and was subsequently diagnosed with AD. “This was a chance discovery”, says Lu, “and in this study, we wanted to see if we could replicate the finding”. Lu and colleagues from the University of California assessed and compared the iconic memory of two groups: 11 elderly adults (average age 84·8 years) with MCI and 16 elderly adults without cognitive decline. Comparisons were also made between the group of people with MCI and a second control group of 23 young adults (Proc Natl Acad Sci USA 2005; 102: 1797–802). Study participants with MCI scored substantially worse than controls of the same and younger age in many neuropsychological tests. Both groups of elderly participants, however, had equivalent skills in precue or visibility tests and on assays of short-term memory. But the group of participants with MCI had a substantial deficiency in iconic memory duration (0·07 s vs 0·30 s) when compared with the elderly control group. “The drugs currently used to treat Alzheimer’s can only slow the progression of the disease and cannot reverse its course”, says Lu. “The earlier it [AD] can be detected, the sooner we can treat it.” Although results of this study are highly suggestive, Lu cautions that the study needs to be repeated in a much larger population. “It is clear that AD has been working its mischief in the brain for decades before it is clinically diagnosed”, comments Paul D Coleman (University of Rochester Medical Center, NY, USA); he points out that several studies have shown many precursors of AD. “This paper may be less than meets the eye”, he adds, “because it has been preceded by other studies involving more cases and pushing the limits of detection much farther back than is seen here”. Roxanne Nelson Iconic memory loss linked to onset of Alzheimer’s disease Computerised test of iconic memory Will & Deni McIntyre/Science Photo Library Courtesy of Hugo Théoret Figure of eight coil (bottom left) for TMS delivery Rights were not granted to include this image in electronic media. Please refer to the printed journal.
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Transcript of Iconic memory loss linked to onset of Alzheimer's disease
Newsdesk
144 http://neurology.thelancet.com Vol 4 March 2005
Cortical excitability can be facilitated orsuppressed for over 1 h by certainpatterns of short duration, repetitivetranscranial magnetic stimulation(TMS). Researchers from the Institute ofNeurology at University College London(UK) found that low intensity pulses ofTMS at 50 Hz for a short duration have along-lasting after effect on the motorcortex in healthy people (Neuron 2005;45: 201–06). Hugo Théoret (Universitéde Montréal, Canada) believes “thediscovery of an efficient, short, and safemethod of modulating corticalexcitability is a great advance that willlikely impact cognitive research andtherapeutic opportunities”.
Previous attempts to affect theplasticity of people’s brains with
repetitive TMS have had limitedsuccess; the after effect was generallyweak and variable, and the longestafter effect produced (lasting about30 min) required TMS of the sameduration. The UCL research groupapplied the theta burst paradigm—amethod of stimulation that hasproduced long-lasting effects in brainslices after short periods ofstimulation—to the motor cortex ofnine healthy adults. John Rothwell, oneof the researchers, explained, “thetheta burst paradigm is a way ofspacing out the repetitive TMS pulsesso that TMS application is short yet theeffect is long and controllable”.
Before and after the researchersdelivered the sequence of TMS bursts to
the hand area of the motor cortex, theygave a single pulse of TMS to measurethe motor evoked potential at the rightfirst dorsal interosseous muscle of the
New era of transcranial magnetic stimulation
The decline of iconic memory may be a key to the early detection ofAlzheimer’s disease (AD). Elderly peoplewith mild cognitive impairment (MCI)—who commonly develop AD—showedmarked deficiencies in iconic memory,according to a recent study.
Iconic memory is a very brief snapshotof a visual stimulus, and lasts about300–500 ms before fading. Lead authorZhong-Lin Lu (University of SouthernCalifornia, CA, USA) first became awareof the potential link between shortenediconic memory and AD several years ago
when studying iconic memory among agroup of volunteers. A healthy 58 yearold man, who was not suffering fromany type of cognitive decline and whowas employed in a very high-profile job,puzzled the researchers by his lack oficonic memory. 2 years later he was nolonger able to do his job because ofmemory decline and was subsequentlydiagnosed with AD. “This was a chancediscovery”, says Lu, “and in this study,we wanted to see if we could replicatethe finding”.
Lu and colleagues from the Universityof California assessed and compared theiconic memory of two groups: 11elderly adults (average age 84·8 years)with MCI and 16 elderly adults withoutcognitive decline. Comparisons werealso made between the group of peoplewith MCI and a second control group of23 young adults (Proc Natl Acad Sci USA2005; 102: 1797–802).
Study participants with MCI scoredsubstantially worse than controls of thesame and younger age in manyneuropsychological tests. Both groupsof elderly participants, however, hadequivalent skills in precue or visibility
tests and on assays of short-termmemory. But the group of participantswith MCI had a substantial deficiency iniconic memory duration (0·07 s vs0·30 s) when compared with the elderlycontrol group.
“The drugs currently used to treatAlzheimer’s can only slow theprogression of the disease and cannotreverse its course”, says Lu. “The earlierit [AD] can be detected, the sooner wecan treat it.” Although results of thisstudy are highly suggestive, Lu cautionsthat the study needs to be repeated in amuch larger population. “It is clear thatAD has been working its mischief in thebrain for decades before it is clinicallydiagnosed”, comments Paul D Coleman(University of Rochester Medical Center,NY, USA); he points out that severalstudies have shown many precursors ofAD. “This paper may be less than meetsthe eye”, he adds, “because it has beenpreceded by other studies involvingmore cases and pushing the limits ofdetection much farther back than isseen here”.
Roxanne Nelson
Iconic memory loss linked to onset of Alzheimer’s disease
Computerised test of iconic memory
Will
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Figure of eight coil (bottom left) for TMS delivery
Rights were not granted to includethis image in electronic media. Please
refer to the printed journal.
