Person:

Daffner, Kirk

OBJECTIVE: To better understand apathy and disengagement in patients with Alzheimer's disease (AD), the authors investigated possible behavioral mechanisms underlying diminished novelty-seeking activity in patients with probable AD. BACKGROUND: Apathy and disengagement have been shown to be the most common behavioral changes associated with AD. METHOD: Patients and age-matched normal controls had their eye movements recorded while pairs of line drawings pitting an incongruous figure against a congruous figure were shown on a screen for 12 seconds. Characteristics of a subset of AD patients who were indifferent to novel visual stimuli as measured by exploratory eye movements were compared to those of a subset of AD patients who were attracted to novel stimuli to a degree similar to that of normal controls. RESULTS: The indifferent patients were judged by informants, who completed a personality questionnaire, to exhibit a greater degree of apathy. The two AD groups did not differ in overall dementia severity or performance on a Saccade-to-Target Task that required shifts of attention and gaze. In a separate task, the indifferent patients were able to accurately identify the more novel stimuli in 97.5% of trials. Normal control subjects exhibited a strong bias toward processing novel stimuli, directing a higher proportion of their first fixations and dwell time to the incongruous stimuli whether the analysis was run for 3, 6, or 12 seconds of viewing. Indifferent patients did not direct their initial fixation toward novel stimuli and distributed their looking time evenly between incongruous and congruous stimuli throughout all measured intervals. CONCLUSIONS: The results suggest that the indifference to novelty observed in some patients with probable AD cannot simply be attributed to global cognitive decline, more elementary attentional deficits, more rapid habituation of response to novel stimuli, or an inability to discriminate upon demand between stimuli of varying degrees of novelty. It is more likely that their behavior reflects a disruption, by AD pathology, of neural systems that modulate behavioral engagement and maintain attentional bias toward novel events in the environment.

Two adult patients are described who suffered bilateral prefrontal damage early in life and who subsequently came to psychiatric attention because of severely aberrant behaviour. A battery of developmental psychology paradigms (not previously used to assess neurologically impaired individuals) showed that social and moral development of these 2 patients was arrested at an immature stage. In comparison with other types of brain damage which disrupt cognitive development, frontal damage acquired early in life appears to provide the neurological substrate for a special type of learning disability in the realms of insight, foresight, social judgement, empathy, and complex reasoning.

Clinical accounts of Alzheimer's disease (AD) suggest that some patients exhibit markedly diminished curiosity and initiative early in the course of their illness. Such behavioral changes are extremely difficult to measure experimentally. We studied one aspect of curiosity by measuring exploratory eye movements in response to provocative visual stimuli in 12 patients with probable AD and 10 matched controls. Subjects viewed slides, each of which contained an incongruous or irregular figure paired with a congruous or regular one. Unlike controls, who spent significantly more time viewing the incongruous stimuli, AD patients distributed their viewing time equally and spent significantly less time than controls looking at the novel stimuli. Additionally, when presented with picture slides containing an unexpected element, AD patients exhibited diminished visual exploration overall and decreased attention to the incongruous part. Further analyses suggest that the results cannot be adequately explained by a general decline in cognition or by problems with ocular motility or directing visual attention. We conclude that AD patients exhibit diminished curiosity which can be measured by the study of exploratory eye movements.

Currently Alzheimer's disease, which affects more than 20 million people worldwide, can only be definitely diagnosed by histological examination of brain tissue obtained at autopsy or biopsy. There is a great need for an early, noninvasive, sensitive, and easily administered diagnostic test of Alzheimer's disease. Here it is reported that patients diagnosed with probable Alzheimer's disease by standard clinical criteria exhibited a marked hypersensitivity in their pupil dilation response to a cholinergic antagonist, tropicamide, placed in their eyes. It was possible to distinguish 18 of 19 individuals (95%) either clinically diagnosed with Alzheimer's disease or classified as suspect Alzheimer's individuals by neuropsychological screening from 30 of 32 normal elderly controls (94%).