Being too smart for your own good:

Issues in the cognitive assessment of

high-functioning individuals

Greg Savage CCD & Department of Psychology, Macquarie University

Co-leader, Clinical & Cognitive Stream, AIBL

Case : 72 year old CEO

referred by neurologist with 4 year history of

• word-finding difficulty, forgetfulness, spatial disorientation while driving

but

• well oriented and informed, ADL OK, still seeing clients, running company, driving to work

Intelligence has a normal distribution

• this is true of most aspects of cognition we assess

Intelligence has a normal distribution

• this is true of most aspects of cognition we assess

For an average individual, scores placed here are clearly abnormal…

But what about scores placed here?

16%

-1 SD

But what about scores placed here?

2%

-2 SDs

But what about scores placed here?

7%

-1.5 SDs

But what about scores placed here?

at least 1.5 SDs below normative mean

b/w 1.5 SDs below and above normative mean

at least 1.5 SDs above normative mean

*CVLT-II: Tot1-5/SDFR/LDFR/d’ *Rey figure copy *Category fluency/switching *Digit Symbol-Coding Brixton

*Digit Span *Rey figure recall *Letter fluency *Boston naming Digit Symbol-Copy Mental Control Picture Completion Similarities Faces-I

Faces-II

MCI : objective evidence of impairment

• 1.5 SDs below normative mean

Impaired: at least 1.5 SDs below normative mean

Intact: ??? b/w 1.5 SDs below and above normative mean

Intact at least 1.5 SDs above normative mean

*CVLT-II: Tot1-5/SDFR/LDFR/d’ *Rey figure copy *Category fluency/switching *Digit Symbol-Coding Brixton

*Digit Span *Rey figure recall *Letter fluency *Boston naming Digit Symbol-Copy Mental Control Picture Completion Similarities Faces-I

Faces-II

MCI : objective evidence of impairment

• 1.5 SDs below normative mean

Clinical judgments about cognitive deficits are based on normative data, which adjust for

• age (nearly always)

• sex (sometimes)

• education (sometimes)

These adjustments work well for the average person

“Our culture encodes a strong bias either to neglect or ignore variation. We tend to focus on measures of central tendency, and as a result we make some terrible mistakes, often with considerable practical import.” Gould (1996)

Elephant in the room…

• research assumes everyone is average

What about the rest of the population?

Need to adjust for case-specific expectations

• premorbid ability

How do we know what our expectations should be?

Neuropsychologists test for preserved abilities

• scores on tests resistant to brain damage

WTAR : Wechsler Test of Adult Reading

50 words, simply read aloud

• can’t sound them out correctly (eg aisle)

• need to know them

• correlates highly with IQ

• word reading is preserved in most brain disorders

• a kind of fossil record…

Our case scored 48/50 : predicted IQ of 117

-1.5 SDs

-1.5 SDs premorbid

IQ=117

case -1.5 SDs

premorbid IQ=117

What if I had seen him 3 years ago, after a year of noted difficulties?

Worried well? Functioning adequately enough

• has it mattered?

In an era of disease-modifying therapy, it definitely would have mattered

• might have been considered unimpaired

• missed out on treatment

How do high-functioning people ‘hold up’?

Cognitive Reserve : Stern (eg 2009, Neuropsychologia)

• no direct relationship between brain pathology and cognitive or functional consequences of pathology

• individual differences in susceptibility

• differences in how tasks are processed

• use your wits on assessment, in daily life

• my case : looked for distinctive features on faces

IQ : a proxy for cognitive reserve

• high IQ would be protective against the impact of brain illness

• against the dementia in Alzheimer’s disease

• but not the disease itself

• cognition/function would remain intact for longer, but unravel very rapidly at some late time-point

• too late for intervention?

• too smart for their own good…

Stern, Neuropsychologia 2009

Back to the research context:

• for any case who normally thinks better than average, we will underestimate impairment using any criterion based on the normative mean

• the converse is also true

AIBL participants are high-performers

• cognitive test scores in HCs are ~0.7 SDs above average

• systematic under-representation of incidence of, and transition to, MCI

• in more than half our sample?

My focus is on transition from healthy cognition to MCI

• it’s where the psychometrics count

• transition from MCI to AD has less reliance on psychometrics

• parallel issues : what counts as functional impairment for a high performer?

AIBL -1.5 SDs (=-0.7)

AIBL HCs premorbid

IQ=112 (+0.8)

0 -1 -1.5 +1 +1.5

Could use regression techniques to account for variation around the AIBL means for cognitive variables

Exploit bimodality revealed by latent class modeling:

• A+ : “slightly above average” cognition

• A++ : “well above average” cognition

A+ (N=311) A++ (N=442)

58% female 45% female

70.7 years old 70.2 years old

56% tertiary educ’n 57% tertiary educ’n

WTAR-predicted IQ=110 (+0.67 SDs) WTAR-predicted IQ=114 (+0.93 SDs)

Test A+ A++

CVLT-II delayed recall +0.34 +1.45

Rey figure delayed recall +0.12 +1.11

Category fluency +0.39 +1.40

Letter fluency +0.28 +1.28

Processing speed +0.36 +0.87

0 -1 -1.5 +1 +1.5

A+ A++

A+ (N=442) A++ (N=311)

58% female 45% female

70.7 years old 70.2 years old

56% tertiary educ’n 57% tertiary educ’n

WTAR-predicted IQ=110 (+0.67 SDs) WTAR-predicted IQ=114 (+0.93 SDs)

26% PiB+ (27/103) 34% PiB+ (25/74)

-1.5

-1

-0.5

0

0.5

1

1.5

2

Baseline 18 mths 36 mths

A++ PiB- (N=49)

A+ PiB- (N=76)

Delayed recall

-1.5

-1

-0.5

0

0.5

1

1.5

2

Baseline 18 mths 36 mths

A++ PiB- (N=49)

A++ PiB+ (N=25)

A+ PiB- (N=76)

A+ PiB+ (N=27)

Delayed recall

-1.5

-1

-0.5

0

0.5

1

1.5

2

Baseline 18 mths 36 mths

Delayed recall

?

?

-1.5

-1

-0.5

0

0.5

1

1.5

2

Baseline 18 mths 36 mths

Delayed recall

?

Cognitive reserve is noise : remove from the equation

• WTAR is a good idea : deceptively simple, and impervious to strategic influence

• blunt instrument, low ceiling

• trivial difference between A+ and A++ groups

• doesn’t target those with nonverbal strengths • declining high-PIQ individuals will be missed

• look for intra-individual discrepancies

• early memory decline relative to non-memory cognition

Use tests which are immune to the impact of CR?

• ‘harder’ tests with little apparent structure?

• no—that just narrows the field

• ‘easier’ tests which tap automatic, not strategic, processing

• reaction time and error rate on easy tasks?

• CogState

With special thanks to:

Dr Petra Graham Department of Statistics, Macquarie University

CSIRO Mathematics, Informatics & Statistics

Dr Andrew Jones Department of Psychology, Macquarie University

CSIRO Mathematics, Informatics & Statistics