Mohammed T. Abou-Saleh

148 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYsample of over 3000 healthy normal subjects in the USA 6 . Thisstudy revealed some interesting differences among the tests. Forexample, the name–face association task administered to 1547individuals showed a decade-by-decade decline in performancebeginning in mid-life, whereas a facial recognition paradigmrevealed decline only in the 70+ group in another survey of326 subjects. Moreover, in the latter study, performance wasmost impaired at a delay interval of 0 seconds, suggestingattentional rather than mnemonic dysfunction.The most important theme of the Everyday Memory Battery,which still makes it of contemporary interest, is its adherence tothe principle of ecological validity—cognitive functions are testedin the context of everyday functions, which makes them relevantto patient and clinician alike. This is clearly an important elementof assessment, but it should also be pointed out that it may be atthe expense of test sensitivity, inasmuch that patients can resort toa greater extent on well-learned routines, to overcome deficits thatwould be exposed by more abstract or unfamiliar test material. Inthis sense the following two batteries to be considered place lessweight on ecological validity and more on theoretical issues, suchas the nature of the brain systems damaged in dementia, as well ason practical considerations that enhance the sensitivity andstability of the results obtained.CANTAB (CAMBRIDGE NEUROPSYCHOLOGICALTEST AUTOMATED BATTERY)CANTAB was developed by a group including Dr T. W. Robbinsat the University of Cambridge and Dr B. J. Sahakian (Section ofOld Age Psychiatry, Institute of Psychiatry) from a researchprogramme funded by the Wellcome Trust to improve thecomparative assessment of cognition from animals to humans.CANTAB is a set of computerized neuropsychological testbatteries with three main components 4,13 :1. Visual memory. Consists of short pattern and spatialrecognition memory tests, a simultaneous and delayedmatching-to-sampletest, and a test of paired-associate,conditional learning of pattern–location associations 14 .2. Attention. Consists of tests of intradimensional and extradimensionalset-shifting (analogous to the Wisconsin CardSorting Test), a reaction time-based visual search task forconjunctive features, according to the Sternberg paradigms 15 ,and a test of sustained attention, termed rapid visualinformation processing.3. Spatial working memory and planning. Consists of tests ofspatial span, spatial working memory and a computerizedversion of the Tower of London task, which includes separatemeasures of thinking and movement time 16 .Each battery employs a touch-sensitive screen and begins withpreliminary tests of sensorimotor function, which enable subjectswith marked visual or motor deficits to be screened out fromsubsequent testing. The theoretical rationale for the tests is basedon two major themes: first, those animal tests of cognitivefunction (e.g. delayed matching to sample, spatial workingmemory and the attentional shifting task, which is based onanimal learning theory) that have proved useful in establishing theneural substrates of certain types of cognitive function and can beadapted appropriately for human subjects; and second, acomponential analysis of cognitive function, allowing thecharacterization of elementary processes contributing to cognition.This is exemplified in each battery, e.g. visual memory,where there are separate tests of spatial and pattern recognitionmemory, as well as a test in which patterned information has tobe remembered in specific spatial contexts. In the attentionalbattery, the attentional shifts are preceded by stages establishingthe subject’s capacities for simple rule use, acquisition of asimple rule (simple discrimination), its reversal, and itsapplication to more complicated stimuli with additionalperceptual dimensions. In the planning battery, some of thecomponential cognitive requirements for the Tower of Londonplanning task itself, such as the capacities of subjects toremember and use a short spatial sequence, and to employworking memory in a strategic spatial search task, areseparately measured. In addition, a ‘‘yoked motor control’’ isemployed, which allows the computation of thinking time,corrected for any problems of movement that inevitablyconfound the interpretation of latency measures in braindamagedand elderly subjects 16–17 . This yoked control isavailable to capitalize on some of the advantages conferredby computerized testing; the exact sequence of moves that apatient uses in attempting to solve a problem is stored on-line,and played back to him/her one at a time, in the yoked controltest.The ‘‘componential’’ approach also has some more practicalbenefits. For example, each test, in addition to containing internalcontrols, begins at a simple level, so that virtually all subjectsachieve a score above floor levels. Moreover, if successful, asubject proceeds to difficult versions of the same test, which avoidsceiling effects. In addition, as the tests are non-verbal in nature,they avoid problems posed by specific language disorders and byilliteracy, and this also makes the tests suitable for cross-nationalstudies. Finally, the tests are available for the IBM machines orsimilar clones running under WINDOWS ’95 or later, which arerelatively inexpensive as well as portable (in fact, CANTAB canbe implemented on a portable computer equipped with atouchscreen) and so can be used by moderately equipped clinicalneuropsychology departments of hospitals, as well as for testing insubjects’ or patients’ homes 4,13 . The tests are both comprehensive,in terms of the range of cognitive functions they cover, and alsosensitive to deficits in patients with dementia of the Alzheimertype (DAT), Parkinson’s disease (PD), Huntington’s disease anddementia of the Lewy body type 14–20 . Some of the deficits haveshown double dissociations across these groups. For example, PDpatients show deficits on matching-to-sample, independently ofdelay, whereas patients with DAT exhibit a delay-dependentdecline in performances. In addition, DAT patients early in thecourse of the disease can perform better than non-medicated,early-in-the course patients with Parkinson’s or Huntington’sdiseases in tests of attentional shifting 15,18,19 . These results areimportant in showing different profiles of deficits in differentforms of neurodegenerative cognitive disorders, which may proveimportant in the early detection and diagnosis of neurodegenerativediseases and for establishing the neural substrates of theearly forms of dementia. For example, it seems likely that theimpairments in visual recognition memory that occur early inthe course of DAT may reflect temporal lobe deficits, whereas theimpairments in attention shifting in unmedicated Parkinson’sdisease 15 and Huntington’s disease 19 may depend upon frontostriatalforms of dysfunction. Other studies have confirmed thatthe spatial working memory and planning tests, as well as that ofattentional shifting, are sensitive to frontal (but not temporal)lobe damage in humans 16,21 .In the assessment of dementia the results are importantbecause the computerized tests may prove to be more sensitiveto cognitive decline than many of the existing instruments, e.g.Mini-Mental State Examination (MMSE) 22 and clinical stagingsof dementia 23 . Follow-up testing in populations of DAT andelderly depressed patients with the visual memory battery hasshown that many of the tests are sensitive to the effects ofprogressive intellectual decline in the DAT patients and to theeffects of recovery in the depressed group 24 . Some studies haveprovided evidence that one of the CANTAB tests (paired