Selective attention in Alzheimer's disease: characterizing cognitive subgroups of patients

Semantic Priming from Uncued Distractors in Alzheimer's Disease

RESEARCH QUESTION

Are semantic impairments in Alzheimer's disease (AD) partially due to deficits in spatial attention?

METHODS AND RESULTS

In a target detection task, both older adults (OAs) and AD individuals were facilitated by valid spatial cues, but only OAs were impaired by invalid cues compared to neutral. In a reading task, spatial cues validly or invalidly cued the location of pictures, which were related or unrelated to subsequent, centrally presented, words. OAs showed semantic priming only after valid cues, whereas AD individuals showed priming after valid and invalid cues.

DISCUSSION

Failure to inhibit uncued locations results in processing of potentially distracting semantic information in AD.

The effects of environmental barriers on the attention span of Alzheimer's disease patients

Anecdotal evidence indicates that Alzheimer's disease patients often appear confused and unable to concentrate, and that this may be related to attention span. This study utilizes barriers of three different heights to test how visual and auditory distracters affect the ability to concentrate on a given task. Residents were given art projects with adult themes and were observed for number of distractions. The results indicate that both low and high barriers are more effective than no barriers in screening out extraneous visual and auditory distractions. Of equal or greater importance is the finding that residents in the early and middle stages of the disease averaged 16 minutes of focused attention in a 20 minute trial.

The septo-hippocampal system, learning and recovery of function

We understand this review as an attempt to summarize recent advances in the understanding of cholinergic function in cognition. Such a role has been highlighted in the 1970s by the discovery that dementia patients have greatly reduced cholinergic activity in cortex and hippocampus. A brief anatomical description of the major cholinergic pathways focuses on the basal forebrain and its projections to cortex and hippocampus. From this distinction, compelling evidence suggests that the basal forebrain --> cortex projection regulates the excitability of principal cortical neurons and is thereby critically involved in attention, stimulus detection and memory function, although the biological conditions for these functions are still debated. Similar uncertainties remain for the septo-hippocampal cholinergic system. Although initial lesions of the septum caused memory deficits reminiscent of hippocampal ablations, recent and more refined neurotoxic lesion studies which spared non-cholinergic cells of the basal forebrain failed to confirm these memory impairments in experimental animals despite a near total loss of cholinergic labeling. Yet, a decline in cholinergic markers in aging and dementia still stands as the most central piece of evidence for a link between the cholinergic system and cognition and appear to provide valuable targets for therapeutic approaches.

Operant Conditioning with Subjects Suffering From Dementia

Two experiments are reported in which patients who resided on continuing care psychogeriatric wards were exposed to an operant conditioning procedure. In the first experiment, the subjects were three female patients, all of whom were suffering from severe dementia. For two of the subjects, extended acquisition training was required before evidence of learning was found. Responding under fixed interval (FI) schedules of three different durations was well maintained by the third subject. Evidence of temporal control was found. The second experiment was a partial replication of the first. The subjects were two male patients who were suffering from mild to moderate degrees of dementia. They were exposed to FI schedules of three different durations. Responding was maintained for the 16 sessions of the study. Procedural modifications as well as some broader implications of these results are noted.

Stereotypes, stereotype threat and ageing: implications for the understanding and treatment of people with Alzheimer's disease

Over the past 15 years, a growing body of research has shown that people with Alzheimer's disease (AD) are affected not only by brain neuropathology but also by their reactions to its effects, by the environments in which they live, and by how they are treated by others. Nevertheless, three relatively neglected social influences on people with AD remain to be examined: negative stereotyping, negative self-stereotyping and stereotype threat. Numerous studies reviewed in this paper indicate that: (1) negative self-stereotypes at conscious and unconscious levels can have adverse effects on the performance of healthy elderly people on tasks demanding explicit memory (recall in particular), and (2) the mere threat of being stereotyped negatively can have adverse effects on the performance of healthy elderly people on tasks including those involving memory. In this paper, we discuss the relevance of these phenomena for our understanding and treatment of people with AD who are exposed to negative stereotypes about old age and about AD before and after they are diagnosed. There is evidence to suggest that these influences may have significant effects on people with AD. The paper concludes with recommendations for best practice in the treatment of people with AD in the light of the most apparent effects of negative self-stereotyping and stereotype threat. These include advocacy for an approach that involves aspects of counselling.

Specific Impairments of Selective Attention in Mild Alzheimer’s Disease

The aim of the present study was to evaluate selective visual attention in subjects affected by Alzheimer's Disease (AD), by means of a computerized spatial exploration test that adopts a Touch Screen (TS) interface, which has already proved able to characterize alternative strategies in performing search tasks. We assessed a group of 16 patients affected by mild to moderate AD, comparing them with 16 control subjects matched for age and education. In the experimental tasks the performance of the AD patients was worse than that of the normal elderly, both quantitatively (slower speeds) and qualitatively (poorer planning and higher number of omissions and perseverations). In the visual attention tasks there appeared to be no close connection between AD patients' performance and increased Reaction Times (RT); this evidenced a specific role of non-elementary cognitive structures enclosed in a higher attentional domain, rather than a general decrease in the speed of basic cognitive processes. Our results are in line with specific AD literature: while psychomotor speed and lower attention levels (sensorimotor) are preferentially impaired in subcortical forms of dementia, the higher levels of selective and divided attention could be the first to deteriorate and appear more markedly disrupted in the Alzheimer type of dementia.

Capacity for decision-making in Alzheimer's disease: selfhood, positioning and semiotic people

The aim of this article is to explore some of the ethical issues surrounding the assessment and determination of capacity of people with dementia in light of their meaning-making ability as shown through discourse. Discourse analysis, two illustrative cases, social construction theory and positioning are used to highlight some of the ethical dilemmas involved in basing a determination of capacity on the diagnosis of dementia and neuropsychological tests of cognitive function. Although neuropsychological tests have their place in assessing some aspects of cognitive function, aspects cognition such as meaning-making ability and selfhood cannot be assessed in a standard format. In dementia, there can be a differential impairment of recall memory while the personality, values and substantial long-term memory remain intact, as does implicit memory for recent events. People with dementia are vulnerable to being negatively positioned, thereby unfairly undermining their rights to make decisions about aspects of their lives. Assessing the capacity of a person with dementia to engage in decision-making is presently in need of examination so as to take into account the person's meaning-making ability and selfhood. Incorrect negative positioning, based on the diagnosis and defects in recall memory, can obscure intact cognitive abilities that allow a person to make decisions about aspects of living, creating the possibility of lasting harm being inflicted on the person with dementia.

Interactions Between Phasic Alerting and Spatial Orienting: Effects of Normal Aging and Alzheimer's Disease

The effects of aging and Alzheimer's disease (AD) on phasic alerting and exogenous spatial orienting were examined within a single precuing task. Phasic alerting decreased with normal aging and was completely eliminated with AD. AD patients also demonstrated an increased spatial orienting effect, attributable to an increased benefit from spatial orienting that was associated with a decreased benefit from nonselective alerting. These results suggest that performance within the precuing paradigm reflects the product of an interaction between nonselective alerting processes and spatially selective orienting processes. The results also highlight the importance of simultaneously assessing alerting and orienting within the same task, because changes attributable to alerting may otherwise be attributed incorrectly to changes in 1 or more processes associated with spatial orienting.

Memory deficits in Alzheimer's disease: the encoding hypothesis and cholinergic function

Forgetting functions generated by delayed matching-to-sample procedures allow delay-dependent effects to be distinguished from delay-independent effects on working memory. Parameters of negative exponential functions estimate initial discriminability (intercept) and rate of forgetting (slope). Forgetting functions for patients with Alzheimer's disease indicate that they differ from normal controls in terms of reduced initial discriminability--that is, in the encoding component of memory performance--but not convincingly in rate of forgetting. Reanalyses of previous studies with different species suggest that pro- and anticholinergic drugs influence initial discriminability in delayed matching-to-sample performance, but not rate of forgetting. The results of our reanalyses are consistent with the conclusion that the cholinergic system plays a role in the encoding component of working memory and that this is the main characteristic of the memory deficit shown by patients with Alzheimer's disease.

Forgetting rates in neuropsychiatric disorders

OBJECTIVE

Previous studies have attributed accelerated forgetting rates on recognition memory tasks to temporal lobe pathology, but findings in some patient groups may have been attributable to metabolic disruption. Findings in psychiatric disorders such as schizophrenia are conflicting. The purpose of the present study was to compare forgetting rates in patients with confusional states (post-electroconvulsive therapy (post-ECT), delirium), with those obtained in schizophrenic patients (with putative temporal lobe pathology), non-ECT depressed patients, and healthy controls. The findings could also be compared with previous reports in patients with head injury, focal structural lesions, and Alzheimer's dementia.

METHODS

Two studies employed a picture recognition task to examine forgetting rates, the first between delays of 1 minute, 15 minutes, and 30 minutes, and the second between delays of 10 minutes, 2 hours, and 24 hours.

RESULTS

There were no significant differences in forgetting rates between 1 minute and 30 minutes, but the ECT group showed accelerated forgetting between 10 minutes and 2 hours compared with healthy controls, associated with a rapid decline in "hit rate". This was not attributable to differential changes in either depression or severity of memory impairment. There were no differences in forgetting rates across the other subject groups.

CONCLUSION

Post-ECT confusional state patients (similarly to "within post-traumatic amnesia" patients with head injury) show accelerated forgetting on a recognition memory task and, in this, they contrast with patients who have focal structural lesions or widespread cortical atrophy. Accelerated forgetting may reflect the effect of disrupted cerebral metabolism on either "consolidation" or memory "binding" processes.

Do amnesics forget colours pathologically fast?

We tested amnesic and control subjects on a task which required the recognition of single, difficult to name colours, after delays ranging from 7 seconds to 120 seconds after performance of the two subject groups had been matched at the shortest delay by giving the amnesic patients longer study time. The amnesic patients showed abnormally fast forgetting over the two minute period. Furthermore, a subgroup of nine subjects with presumed damage to midline diencephalic structures (Korsakoff's syndrome) were found to forget as fast as a group of six subjects with presumed medial temporal lobe damage (herpes simplex encephalitis). These results contrast both with studies using the Huppert and Piercy procedure and those using the Brown-Peterson task, none of which have shown convincing evidence of accelerated forgetting in medial temporal lobe or diencephalic amnesia.

Rates of forgetting in Alzheimer dementia

Patients diagnosed with Alzheimer's disease (AD) were compared with healthy controls on a picture recognition task, a forced choice word recognition task, a forced choice design recognition task, a picture recall task and a stem completion task. Performance on recognition and word stem completion was assessed at 1, 10 and 20 min after exposure to experimental stimuli, as these are delays across which previous studies had suggested there might be differing forgetting rates. AD patients did not show significantly faster rates of forgetting relative to controls on picture recognition, design recognition, word recognition or stem completion, after levels of learning had been matched as closely as possible. Moreover, once initial learning was equated in a small number of subjects, there were no qualitative differences between AD patients and controls following inclusion and exclusion instructions on the stem completion task. In particular, those AD patients who were matched to controls for initial levels of "recollection" showed comparable forgetting rates in recollection (or cued recall). Although matching was more difficult for a picture recall task, both the main analysis and subgroup analysis indicated faster forgetting in the AD group than controls, suggesting a difference between "free recall" and recognition or cued recall measures, comparable with the finding in a parallel study of organic amnesia.

Relating the mechanisms of orienting and alerting

Cues provide two types of information: information about where the target will occur and when it will occur. We hypothesized two underlying processes related to cues, orienting (to location) and alerting. Using a covert orienting task under different conditions of alertness, we found evidence of independence between orienting and alerting (Experiments 3-4). The alerting mechanism is spatially broad and seems common for auditory and visual input (Experiments 1-2). In Experiment 1, visual cues at four locations occur simultaneously to prevent orienting; response facilitation was the same for targets occurring near or far from a cue. In Experiment 2, adding a visual alerting signal to an auditory signal provided no additional benefit. In Experiment 3, an auditory signal was used to modulate the alertness level during a covert orienting task. Orienting, measured by the validity effect, was independent of the level of alertness in this simple reaction task. Experiment 4 extended those results to a choice task. These studies indicate separate mechanisms of alerting and orienting. The global mode of alertness is consistent with the broad axonal distribution of the noradrenergic system. In contrast, human and animal data suggest that the orienting mechanism may be modulated by the basal forebrain cholinergic system.

The nucleus basalis magnocellularis cholinergic system: one hundred years of progress

The nucleus basalis magnocellularis (NBM) contains a population of large cholinergic (Ch) neurons that send their axons to the entire cortical mantle, the olfactory bulbs, and the amygdala. This is the centennial anniversary of the first exact description of this nucleus by Von Kölliker, who named it in honor of its discoverer. This review will focus upon recent attempts to understand the role of the NBM Ch neurons in higher cognitive function by the use of selective lesion analyses and electrophysiological recording techniques. Behavioral deficits associated with NBM lesions produced by injections of excitatory amino acid agonists have been demonstrated in a variety of tasks. Performance decrements produced by these lesions were initially interpreted as being the result of impairments in learning and memory abilities. However, the precise role of the Ch NBM neurons in these performance deficits could not be more thoroughly investigated until it became possible to produce selective and discrete lesions by injection of the immunotoxin, IgG-192 saporin. The results of investigations using this immunotoxin supported a role for NBM Ch neurons in the performance of tasks that require selected attentional abilities rather than learning and memory per se. These lesion analysis studies suggested that the corticopetal NBM Ch system may be involved in the control of shifting attention to potentially relevant, and brief, sensory stimuli that predict a biologically relevant event, such as a food reward. Electrophysiological evidence has implicated NBM Ch cells in the control of attentional processes, as well as a role in the control and maintenance of arousal and sleep states. Electrophysiological studies also suggest that NBM Ch neurons might influence cortical EEG activity in two ways, by its direct excitatory inputs and by an indirect inhibitory projection to the thalamic reticular nucleus. Taken together with the results of histological and anatomical studies of the basal forebrain, NBM Ch cells appear to be ideally located within the basal forebrain for evaluating sensory stimuli for their level of significance, via inputs from the midbrain and limbic system, and also to modulate intrinsic cortical responsiveness appropriately in order to attend to brief, highly salient sensory stimuli.

Improvement of picture recall by repetition in patients with dementia of Alzheimer type

The evidence for positive effects of repetition on recall performance in patients with dementia of Alzheimer type is equivocal. This may be due to the difference repetition conditions used. The aim of this study was therefore to evaluate the effects of different repetition modes on the improvement of recall performance in demented subjects. Twenty-four patients with Alzheimer type dementia and 24 control subjects with remitted depression were included in the study. Pictures were presented repeatedly using different presentation modes at a constant total presentation time. Free recall was tested repeatedly after different periods of delay (0-8 hours). Immediate and delayed list repetition significantly improved recall performance in both groups. Within-list repetition did not improve total recall in demented subjects. The repeated measurement design sensitively detected minor changes in recall performance. These were not observed using other measures of recall and recognition (hits, false alarms, indices of signal discrimination).

Central cholinergic systems and cognition

The organization and possible functions of basal forebrain and pontine cholinergic systems are reviewed. Whereas the basal forebrain cholinergic neuronal projections likely subserve a common electrophysiological function, e.g. to boost signal-to-noise ratios in cortical target areas, this function has different effects on psychological processes dependent upon the neural network operations within these various cortical domains. Evidence is presented that (a) the nucleus basalis-neocortical cholinergic system contributes greatly to visual attentional function, but not to mnemonic processes per se; (b) the septohippocampal projection is involved in the modulation of short-term spatial (working) memory processes, perhaps by prolonging the neural representation of external stimuli within the hippocampus; and (c) the diagonal band-cingulate cortex cholinergic projection impacts on the ability to utilize response rules through conditional discrimination. We also suggest that nucleus basalis-amygdala cholinergic projections have a role in the retention of affective conditioning while brainstem cholinergic projections to the thalamus and midbrain dopamine neurons affect basic arousal processes (e.g. sleep-wake cycle) and behavioral activation, respectively. The possibilities and limitations of therapeutic interventions with procholinergic drugs in patients with Alzheimer's disease and other neurodegenerative disorders in which basal forebrain cholinergic neurons degenerate are also discussed.

Unilateral spatial neglect in Alzheimer's disease. A line bisection study

Neuropsychological studies on Alzheimer's disease (AD) have rarely mentioned about unilateral spatial neglect in spite of widespread use of visuospatial tasks. We reported a 62-year-old woman with probable AD who showed moderate dementia with left unilateral spatial neglect and relatively preserved language function. An extensive line bisection study with either hand confirmed her having left unilateral spatial neglect. Single photon emission computed tomography revealed relative hypoperfusion in the right temporal and parietal regions. AD patients with disproportionate right hemisphere dysfunction may exhibit left unilateral spatial neglect if tested adequately in the stage of mild to moderate dementia. We consider that application of the line bisection test to AD patients contributes to estimation of their right hemisphere function.

Cognitive functions of the basal forebrain cholinergic system in monkeys: memory or attention?

The cholinergic hypothesis of memory dysfunction originally proposed that dysfunction of cholinergic neurons in the basal forebrain cholinergic system (BFCS) may be responsible for the memory deficits associated with aging and Alzheimer's disease (AD). This hypothesis directed focus on the BFCS in experimental animal models of AD. In contrast to numerous studies in rodents, fewer investigations have been conducted in monkeys with BFCS lesions. The medical septal nucleus/nucleus of the diagonal band of Broca (MS/NDBB) and the nucleus basalis of Meynert (NBM) may be involved in different cognitive functions in monkeys. Although few investigations have specifically addressed the issue of cognitive functions of the MS/NDBB in monkeys, there is some indication that these regions may be important for memory. In contrast, lesions of the NBM do not consistently disrupt mnemonic functions in monkeys. Recent electrophysiological and lesion studies of monkeys indicate that the NBM may play a more important role in attention functions, impairments of which are an early and significant feature of patients with AD.

Effect of scopolamine on visual attention in rats

In the present study, the effects of scopolamine (SCOP) were determined upon the performance of rats in the five-choice serial reaction time task, a test of attention analogous to the continuous performance test in man. Rats were trained to detect and respond to brief flashes of light presented randomly in one of five locations until a stable level of performance was reached. SCOP (0.03-0.1 mg/kg SC) was administered 30 min prior to testing under standard conditions of stimulus presentation. SCOP reduced response accuracy at the highest dose and dose-dependently increased omissions and perseverative responses. However, these effects were mimicked by scopolamine methylbromide (SCOPMBr) which might suggest a peripheral site of action. When the task difficulty was increased by manipulating the stimulus presentation parameters, i.e. reduced stimulus intensity, duration or temporal predictability, SCOP (0.075 mg/kg SC) failed further to impair performance accuracy. However, in two separate experiments, SCOP (0.075 mg/kg SC) robustly increased the distractibility caused by a burst of loud white-noise occurring unpredictably during the intertrial-interval: SCOP significantly decreased accuracy and increased omissions, magazine latency, premature and perseverative responses compared with vehicle and the equivalent dose of SCOPMBr. These findings provide further evidence of a role for the central cholinergic system in attention.

Do amnesics forget faces pathologically fast?

In 1978, Huppert and Piercy introduced a general method for comparing forgetting rates across groups differing in their baseline memory performance. The method has since become a standard for measuring rate of forgetting in amnesia. Using this method, amnesic subjects with presumed damage to midline diencephalic structures have consistently been reported to forget at a normal rate whereas patients with medial temporal lobe damage have sometimes been reported to forget pathologically fast. Conclusions about amnesic forgetting rates using Huppert and Piercy's procedure, however, are unsafe because the matching procedure results in the shortest mean item-presentation-to-test delay being longer in amnesics than control subjects. A further problem with previous work is that frequently the shortest delay at which performance is measured is 10 minutes. An alternative procedure to Huppert and Piercy's is outlined which eliminates the matching confound. An experiment was carried out using this procedure with face stimuli, and with amnesic and control performance matched immediately following study, and then tested at delays of 5, 12, and 30 minutes. Pathologically fast forgetting was observed in a group of 19 amnesics over the first 5 minutes, but between 12 and 30 minutes their controls forgot faster so that the two groups had forgotten the same amount after 30 minutes. A subgroup of nine Korsakoff patients, with probable damage to midline diencephalic structures, showed a similar abnormal forgetting pattern to the remaining 10 amnesics, some of whom had medial temporal lobe damage. A retroactive interference condition was also included for the 12 minute condition at which delay patient and control recognition was mildly and equivalently disrupted. For unknown reasons perhaps related to a storage abnormality, amnesics lose face recognition memory sooner in the first 30 minutes of forgetting than do normal people, who show accelerated forgetting later so as to match patients after 30 minutes delay.

Detection and staging of early clinical dementia

In order to find neuropsychological indicators for detection and staging of dementia, groups of very mild, mild, and moderate dementia were compared to healthy aged individuals in neuropsychological tests tapping various cognitive and finger-motor functions. Results showed that the groups differed significantly in all cognitive tests, but not in the finger-motor tests. A stepwise discriminant analysis indicated that detection of very mild dementia was best accomplished by three tests assessing episodic memory, semantic memory, and visuospatial functioning. Staging of dementia was best accomplished by means of only one canonical function based on tests tapping episodic memory, semantic memory, visuospatial functions, and psychomotor speed. These results indicate that the pattern of dysfunction is similar for different levels of dementia, suggesting that similar cognitive functions may be involved in detection and staging of dementia.

Heterogeneity of brain gene expression in Alzheimer's disease

We have examined the expression of several genes whose transcripts have increased levels in Alzheimer's disease and have found heterogeneity in these levels in different patients with this condition. The level of expression of these genes was compared to different clinical and pathological aspects of the disease. A case with markedly elevated alpha 1-antichymotrypsin mRNA levels demonstrated prominent neuronal accumulation of this protein. Many of the neurons which demonstrated alpha 1-antichymotrypsin staining did not have neurofibrillary tangles, and vice versa. This suggests that alpha 1-antichymotrypsin staining might identify a different facet of the pathology of Alzheimer's disease than does neurofibrillary tangle staining and may provide new information in the study of this condition.

Directed and divided attention in Alzheimer's disease: impairment in shifting of attention to global and local stimuli

This study investigated the relative performance of Alzheimer's disease (AD) patients and normal controls on directed and divided attention reaction time (RT) tasks that involved the use of global-local stimuli (e.g., a large '1' made from small '2s'). Relative to normals, AD patients displayed disproportionately greater impairment on the divided attention task compared to the directed attention task. On the divided attention task, when the target remained at the same global-local level across consecutive trials, the AD patients displayed a greater facilitation effect than did the controls when responding to the second stimulus. However, when the target changed levels across consecutive trials (i.e., from the global to the local, or vice versa) the AD patients' RTs to the second stimulus were disproportionately slower than were the controls' RTs. These results demonstrated that AD patients are impaired in disengaging and shifting attention across levels of perceptual organization within the same stimulus.

Letter matching: effects of age, Alzheimer's disease, and major depression

We compared Alzheimer's disease (AD) patients and Major Depressive Disorder (MDD), Aged normal, and Young normal controls on a letter-matching task designed to measure the time needed to access overlearned linguistic information in long-term memory. Name identity (NI) and physical identity (PI) reaction time and the NI-PI difference were compared for ADs, MDDs, and Aged normals and separately for Aged and Young normal groups. AD subjects had slower NI and PI reaction times and a bigger NI-PI difference than Aged normal and MDD subjects, suggesting that speed of access to overlearned letter-name information in long-term memory is slowed for ADs. There were no reliable differences between Aged normal and MDD subjects. Aged normals had slower NI and PI reaction times and a bigger NI-PI difference than Young normals, suggesting that the highly practiced operations needed to access letter-name information slow with age. A discriminant analysis was used to evaluate the usefulness of the "easy to perform" letter-matching task for diagnostic purposes. Ninety percent of normal and MDD subjects but only 68% of AD subjects were classified correctly.

Anticholinergic drug effects on quantitative electroencephalogram, visual evoked potential, and verbal memory

Electroencephalographic (EEG) power and coherence spectrum and visual evoked potential (VEP) recordings were made in a group of control subjects on two occasions, a week apart, before and after the subcutaneous administration of either 0.6 mg scopolamine (hyoscine-hydrobromide), a centrally acting anticholinergic drug, or 0.5 mg methscopolamine nitrate, a peripherally acting anticholinergic drug. After scopolamine administration, the EEG power spectrum significantly slowed and EEG coherence at the alpha and beta frequencies decreased. Left interhemispheric coherence increased at 1 Hz and 3-7 Hz. Methscopolamine had no significant effect on the quantitative EEG. The latency of the major positive components of the VEPs, to both flash and pattern stimuli, were not significantly affected by either drug. Verbal memory was significantly reduced after scopolamine. The results suggest that previous reports of scopolamine-induced changes in the EEG power spectrum and in verbal memory can be attributed to the central action of the drug rather than to peripheral side effects.

Alzheimer-type dementia and verbal memory performances: influence of selegiline therapy

In a double blind randomized crossover trial lasting 6 months selegiline, a selective MAO-B inhibitor, was tested against placebo for activity on verbal memory performances in Alzheimer-type dementia (DAT). Verbal memory was assessed with the Rey-Auditory-Verbal Learning Test at the start of treatment, at the time scheduled for crossover (90 days) and at the end of the trial (180 days). The results suggest that selegiline possesses significant activity on some memory parameters, which seems to depend on an improvement both in information processing abilities and in learning strategies at the moment of acquisition.

A critical evaluation of monkey models of amnesia and dementia

In this review we consider various models of amnesia and dementia in monkeys and examine the validity of such models. In Section 2 we describe the various types of memory tests (tasks) available for use with monkeys and discuss the extent to which these tasks assess different facets of memory according to present theories of human memory. We argue that the rules which govern correct task performance are best regarded as a form of semantic rather than procedural memory, and that when information about stimulus attributes or reward associations is stored long-term then that knowledge is semantic. The demonstration of episodic memory in monkeys is problematic and the term recognition memory has been used too loosely. In particular, it is difficult to dissociate episodic memory for stimulus events from the use of semantic memory for the rule of the task, since dysfunction of either can produce impairment on performance of the same task. Tasks can also be divided into those which assess memory for stimulus-reward associations (evaluative memory) and those which tax stimulus-response associations including spatial and conditional responding (non-evaluative memory). This dissociation cuts across the distinction between semantic and episodic memory. In Section 3 we examine the usefulness of the classification of tasks described in Section 2 in clarifying our understanding of the contribution of the temporal lobes and the cholinergic system to memory. We conclude that evaluative and non-evaluative memory are mediated by separate parallel systems involving the amygdala and hippocampus, respectively.

Sparing of attentional relative to mnemonic function in a subgroup of patients with dementia of the Alzheimer type

Patients with dementia of the Alzheimer type (DAT) received two tests of visual selective attention, together with tests of spatial and visual recognition memory and visuospatial conditional learning previously used to show deficits early in the course of DAT. One set of attentional tests compared visual discrimination learning along intra- and extra-dimensional shifts, using a "total change" design. In the 12 DAT patients capable of attempting the extra-dimensional shift (subgroup 1), performance was equivalent to that of controls. This subgroup was also unimpaired at simple and compound discrimination learning and reversal and an intra-dimensional shift. They were as accurate as controls on a visual search task requiring matching of stimuli on two dimensions with variable numbers of alternatives, but were significantly impaired in the tests of recognition memory and learning. By contrast, the other 13 patients showed marked impairments in the attentional tasks. This subgroup was also significantly worse than subgroup 1 in performance on the visual recognition and conditional learning tasks, and showed greater severity on most of the clinical ratings of dementia. The sparing of attentional shifting in patients early in the course of DAT is contrasted with the impairments previously described in patients with Parkinson's disease with only mild or absent memory loss. The implications of this double dissociation of deficits for understanding the neural bases of the cognitive deficits in these two neurodegenerative diseases are discussed and their significance for the staging of DAT is considered.

Selective attention in Alzheimer's disease: CSF correlates of behavioral impairments

CSF levels of HVA, 5-HIAA, and free MHPG, the major metabolites of dopamine, serotonin, and norepinephrine respectively, were measured in 22 patients with AD. These 22 patients were also administered tests of picture-recognition and attentional focusing as part of an earlier experiment. A significant association between deficits in attentional focusing and reduced levels of free MHPG in CSF was noted. These results suggest that behavioral measures can identify patients with noradrenergic involvement.