Three primary goals of neuropsychological assessment are: (1) to establish an individual's cognitive and behavioral strengths and weaknesses, (2) to interpret findings from diagnostic viewpoint (e.g. differential diagnosis such as depression versus dementia), (3) to extrapolate treatment and rehabilitation reccomentations  from the neuropsychological findings. This article consist of two main part. First, it provide a general information to neuropsychological assessment in AD. Second, give some example researchs especially little is known about implicit memory in AD.

Definitions of dementia very enormously due to the multifaced nature of the ilness. There are different types of dementia, presenting with a smilar basic symptoms (Alzheimer,Vascular, Lewy Body, Frontal Lobe, and Mixed types). Dementia, particularly Alzheimer type dementia (AD), was one of the major public health problem last 30 years. This led to development of widely accepted two diagnostic criteria for use clinical settings and scientific researches in dementia:  1)  Offered by the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Releated Disorders Association (NINCDS-ADRA) (McKhan et al., 1984). 2) The Diagnostic and Statistical Manual of mental Disordes: 4th Edition (DSM-IV) of the American Psychiatric Association (APA, 1994).

These two criterias are generally consistent of each other. According to these criterias: 1) the dementia is progressive and multiple cognitive decline in elderly persons in the absence of consciousness, presence of disturnances of neurological, or psychiatric conditions that might in and of themselves account for these progressive impairement, 2) These diagnostic criterias include the presence of dementia established by clinical exam and confirmed by neuropsychological testing (APA, 1994; McKhan et al., 1984).   

Cognitive complaints, particularly memeory complaints, are common in old people. Some of these old people experince changes severe enough to seek medical help and, indeed, have objective evidence of cognitive impairement, even though they do not dementia (Ribeiro, Mendoça & Guerreiro, 2006).

Mild cognitive impairment (MCI) is a clinical syndrome to represent the transition between normal cognitive function and dementia. In this stage, the person doesn't yet meet criteria for dementia. Considerable evidence supports the argument that there is a transitional phase between normal function and dementia. Neuropsychological researches of persons defined as neither normal nor demented demonstrate progressive declines in cognitive functions and/or processes over time. These are particularly striking in the area of episodic memory , but other domains appear to be affected as well (Albert & Blacker, 2006; Storandt et al., 2002). These results are consistent with the clinical criterias for dementia require impairment in two or more cognitive funcitons.

The mild cognitive impairement (MCI) criteria provides by Petersen et al. (1991). These criteria were as fallows: 1) subjective memory complaint, 2) objective memory impairement for age and education (standart deviation of 1.5 adjusted mean score of standardized memory test), 3) preserved general cognition for age, 4) intact basic activities daily living, and 5) not demented. The MCI criteria were revized to cinical subtypes (amnestic MCI, non-amnestic MCI, multiple-domain MCI) (Petersen, 2004). The revized criteria also acknowledged the possibility that more than one cognitive area might be impaired within each of these subtypes. The increasing information about MCI as a heterogenous syndrome carries with it the need to clarify the nature of what is normal (Albert & Blacker, 2006).

The neuropsychological tests and test batteries needs to focus on main cognitive areas or functions as the core features of dementia  and memory as a supplemental domain, in order to genuinely identify all cases of dementia. This needs to be incorporated into both the detailed neuropsychological assessment used for to diagnose and to evaluate or to monitor the effects of drug therapy (Voss & Bullock, 2004).

MCI and/or dementia brief mental status examinations , screening tools and laboratory tests are not adequate for diagnosis. Comprehensive neuropsychological assessment consist of different cognitive areas (attention, memory: e.g. immediate, delayed, episodic, procedural) visuo-spatial functions, language, executive functions ) (Mesulam, 2000; Loewenstein et al., 2006; Petersen, 2004).

The existence of implicit memory was first demonsrated in studies conducted with amnesic patients (Graf et al.,1985). Implicit memory defined as the recollection of knowledge unconsciously, automatically and without being aware of, is different than explicit memory which the knowledge is recollected consciously and being aware of.  Different memory functions are measured by traditional explicit memory tests (free recall, cued recall, recognition, etc.) for neuropsychological assessment of AD but, implicit memory is ignored.

The most frequently used implicit memory test/task is Word Stem Completion Task (WSCT) (Blaxton, 1989). The majority of studies found that WSC performance is impaired in AD (Carlesimo et al., 1995; Spaan et al., 2003; 2005). Nonethless, there are other studies showing that WSC performance is not impaired in AD (Golby et al., 2005; Kessels et al., 2005; Russo & Spinler, 1944). According some authors, AD patients perform comparably to normal controls in implicit memory tests that are mainly composed of perceptual components, such as perceptual recognition. These implicit memeory tests are sensitive to physical characteristics of stimulus (Blaxton, 1989; Nebes, 1989).

Failure on conceptual implicit memory tests is a determinant of impairement in semantic coding because conceptual implicit memory tests are sensitive to the semantic characteristics of stimulus ( Monti et al., 1996). However, impairement in semantic information processing or coding may vary according to the stage of AD (mild, moderate,severe)( Braak & Braak, 1991).

There are many studies that AD patients fail in WSC tasks after completing semantic coding tasks (Carlesimo et al., 1995). In contrast, there are various studies showing that patients with AD preserve their WSC performance after performing task that require producing target words (Keane et al., 1991). A succesful semantic coding occurs with correct word production, and semantic representations are protected in implicit memory tasks.

Many studies have used various implicit memory tasks in researching AD, mostly WSC, and it has been shown that there is a selectivity regarding implicit memory, as the conceptual components are impaired (Gabrielli et al., 1994; Spaan et al., 2005).

Conversely, there is inconclusive information about WSC perormance in AD. These controversial findings may be due to using mixed patient groups that are not homogenous and/or  using different neuropsychological test batteries fort he diagnosis of AD.

In our study (Akdemir et al., 2007), our first aim was  to determine if there are differences in WSC scores of AD patients, MCI patients, and a healthy controls. The second aim was to determine wheather there are differences in WSC scores of the groups when stimulus are coded in different level of processing (semantic coding=imagining, physical coding=constant counting, and control). When the findings were evaluated, the main effect of group on implicit memory performance was not significant. This is evidence for intact of the implicit memory function shown by the WSC task in the above mentioned patients groups. The findings of our research support other related study findings in the literature that show implicit memory is not effected by MCI or mild to moderate stage AD when the level of processing variable is held consonant (physical)(Balota & Duchek, 1991; Golby et al., 2005; Kessels et al., 2005; Russo & Spinler, 1994).On the contarary, the finding that severe stage AD patients failed in the physical coding condition in comparison to the MCI group suggested that implicit memory performance impairement occurs in severe stages of AD (Akdemir et al., 2007).  Our study findings are important fort he clinical assessment and understanding of MCI and AD.

Some researchers suggest that implicit memory tests are more powerful in the clinical assessment of early stage AD than commonly used Mini Mental State Examination (MMSE) (Busse et al., 2003; Spaan et al., 2005). Therefore we think is premature to conclude that implicit memory tests are more sensitive than the MMSE. Such a conclusion can only be reached if supported with future research findings. However, we agree with the above-mentioned studies that implicit memory tests should be included in neuropsychological tests used fort he clinical evaluation of AD.

Doç.Dr.Banu Cangöz

Hacettepe University Department of Psychology

Turkey

banucan(at)hacettepe.edu.tr

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