Mohammed T. Abou-Saleh

COMPUTER METHODS OF ASSESSMENT OF COGNITIVE FUNCTION 149associate learning) is capable of discriminating between thosepatients with questionable dementia that go on to be diagnosedwith DAT, and those that do not 25,26 . There is evidence thatsome of the tests are sensitive to drug treatments in DATpatients 27 , as well as to the effects of a variety of drugs innormal subjects, including those that may provide models ofdifferent aspects of dementia 28,29 .CANTAB has also been subject to several forms of validationtesting.There are, for example, data on test–retest reliabilityshowing that most of the tests fall into categories described as‘‘good’’ or ‘‘fair’’ 30–32 , even though many tap ‘‘fronto-executive’’functions that are notoriously unreliable in terms of measurementin this context. Most of the elements of the CANTABbattery have been administered to a large sample of normalsubjects (4800) from the North East Age Research Panel. Thishas resulted in two major publications, which have provided astandardization of the test scores across a wide range of agesand several levels of intelligence 33,34 . There are also burgeoningdata on developmental norms 35 . CANTAB is also validated intheoretical terms, partly from the studies of so many patientgroups, including those with specific damage to differentregions of the neocortex 16,21,36 . There is also a parallelCANTAB battery for testing monkeys, which potentiallyprovides one way of achieving a vertical integration offindings across species 37 . Further data on the underlyingneural substrates of the tests is provided via the availabilityof functional imaging data (mainly derived from positronemission tomography) that confirm which neural networks areactivated by different tests 38–42 .COGDRAS: A COGNITIVEPERFORMANCE BATTERYThe Cognitive Drug Research Computerized Assessment System(COGDRAS) is rather complementary to the other two batteriesdescribed, in that it is based more on pragmatic considerations ofassessing such functions as reaction time and elementary aspectsof memory than on theoretical preoccupations with the ecologicalvalidity or the relationship of task performance to functionalbrain circuitry. COGDRAS was originally designed by Dr KeithWesnes 43 to evaluate the cognitive effects of drugs in normalvolunteers and patients. A further version of the battery(COGDRAS-D) was developed to examine cognitive performancein people with dementia 43,44 . In COGDRAS-D eight cognitivetests are presented to the subject, the system originally havingbeen installed on a BBC microcomputer 43 . The subject faces thescreen with two index fingers resting on two response buttons. Allmaterial is presented visually on the screen in large bold type. Thetests comprise immediate and delayed verbal and picturerecognition, a test of sustained attention similar to that used inCANTAB, simple and choice reaction time tests, and a memoryscanning task. The battery deliberately sets out to avoid problemsolvingtasks or the provision of negative feedback. In variousextensions of the battery, tests of motor control are alsoincorporated. Like CANTAB, it has been employed in a widevariety of applications, especially for testing effects of drugs 45 orpotential environmental toxins in normal subjects.One validation study 44 for the dementia version of the batteryhas assessed 98 unselected patients from a memory clinic, whowere divided into five groups on clinical assessment, includingdemented, depressed, ‘‘worried well’’, minimally cognitivelyimpaired, and other brain disorders. The battery discriminatedbetween some of these groups. In the key comparison of dementiaand minimally impaired patients, 6/14 measures were significantlyworse than for the demented group, although the level ofsignificance obtained for these individual measures was less thanthat achieved by the MMSE. It has also been used to comparepatients with DAT and Huntington’s disease 46 . An earlier study 43showed good test–retest reliability coefficients for dementedpatients, particularly on the reaction time measures and significantcorrelations with other commonly-used instruments indementia research. More recent applications of the battery havealso shown that it is possible to test DAT patients over as long asa 4 h period, in the context of studying the effects of thebenzodiazepine antagonist flumazenil 47 .CONCLUSIONSThe batteries reviewed above, as well as others, will ultimatelyhave to be compared with one another, as well as with moreconventional assessment procedures, and this will require largeand dedicated studies, some of which are under way. A cliniciananxious merely to diagnose DAT and other conditions willunderstandably enquire why such complex tests should supplantthe use of such simple and easy-to-use instruments as the Mini-Mental State Examination 22 . The answer is that they are notintended to supplant, but rather to augment, their use. In our ownexperience, for example, the Mini-Mental State Examinationoften fails to detect the early onset of dementia, especially inindividuals of high IQ. To understand the relationship betweensuch clinical rating scales and the specific computerized tests is toconsider the scale as providing a gross measure on a relativelyundifferentiated range of functions, whereas the computerizedtests provide more specific and precise information aboutparticular capacities, thus providing important information forpatient management.Crook et al. 6 pointed out that they found it useful to developin parallel their own self-rating scales for memory, although therelationships with direct performance measures are typicallylow. Of course, such low correlations may reflect the measurementof subtly different components of memory, all of whichshould be taken into account. They view self-rating data asimportant in assessing age-related memory disorders and familyratings and clinical scales as useful in the assessment ofdementia. Certainly, it is important to relate what may be astatistically significant and consistent effect of a treatment oncomputerized tests of cognitive performance to the clinicalimprovement manifest to the patient’s family in their everydayactivities. However, it should be noted that such assessments ofeveryday activities have not so far proved to be especiallydiscriminating for patients with mild DAT. It is particularlyimportant to add some assessments of everyday activities to theassessments provided by CANTAB and the COGDRASbattery, as these are not specifically designed to simulate suchsituations. The rationale is that the use of rather visual abstractmaterial tends to be more sensitive in detecting deficits than theuse of concrete examples, as there is every indication that manywell-established skills (e.g. reading) or types of knowledge(skills) may remain largely intact in early dementia. Moreover,obvious differences in life experience, e.g. produced by differentoccupations, will tend to be minimized. Finally, we shouldpoint out that it is important that batteries such as CANTAB,and to a lesser extent CDR, can provide means for differentiatingcognitive disorders in the elderly arising from a variety ofconditions, preferably on a qualitative basis. Providing a profileof which functions are spared as well as which are impaired mayhave implications for strategies based on rehabilitation, as well aspharmacological treatments, which will increasingly motivateattempts at cognitive remediation for the elderly.