Cognition following bilateral implants of embryonic dopamine neurons in PD: a double blind study.

OBJECTIVES: To determine if bilateral transplantation of embryonic mesencephalic dopamine cells into the putamen of patients with PD significantly affected their cognitive functioning when compared with patients receiving sham surgery and to examine the effect of age on cognitive performance after implantation. METHODS: Forty patients (19 women, 21 men; age 34 to 75 years) with idiopathic PD of at least 7 years' duration (mean 14 years) who had disabling motor signs despite optimal drug management were randomly assigned to tissue implants or sham craniotomies in a double-blind design. Neuropsychological tests assessing orientation, attention, language, verbal and visual memory, abstract reasoning, executive function, and visuospatial and construction abilities were administered before and 1 year after surgery. Treatment groups did not differ at baseline in demographic, neuropsychological, motor, depression, or levodopa equivalent measures. RESULTS: Postsurgical change in cognitive performance was not significantly different for real or sham surgery groups. Performance in both groups remained unchanged at follow-up for most measures. CONCLUSIONS: Embryonic dopamine producing neurons can be implanted safely into the putamen bilaterally without impairing cognition in patients with PD, but within the first year, improved cognition should not be expected.

Episodic priming and memory for temporal source: event-related potentials reveal age-related differences in prefrontal functioning.

Event-related potentials (ERPs) were recorded from young (M = 25) and older (M = 71) adults during a recognition memory paradigm that assessed episodic priming. Participants studied two temporally distinct lists of sentences (each with two unassociated nouns). At test, in response to the nouns, participants made old-new, followed by remember (context)-know (familiarity) and source (i.e., list) judgments. Both young and older adults showed equivalent episodic priming effects. However, compared to the young adults, the older adults showed a greater source performance decrement than item memory performance decrement. Both age groups showed equivalent posterior-maximal old-new ERP effects. However, only the young produced a frontal-maximal, late onset old-new effect that differed as a function of subsequent list attribution. Because source memory is thought to be mediated by prefrontal cortex, we conclude that age-related memory differences may be due to a deficit in a prefrontal cortical system that underlies source memory and are not likely to be due to an age-related decline in episodic priming.

Item and source memory: differential age effects revealed by event-related potentials.

The neural substrates of age-related memory differences were evaluated by recording event-related potentials (ERPs) from young and older adults during a recognition memory paradigm. Subjects studied two temporally distinct lists of sentences (each with two nouns) and were tested for their memory of the nouns and of the list (i.e. temporal source) in which they had occurred. Compared with the young, the old showed a greater source than item memory performance decrement. Both age groups showed equivalent posterior-maximal old/new ERP effects. However, only the young produced a frontal-maximal, late onset old/new effect that differed as a function of subsequent source attribution. Age-related explicit memory differences may be due to a deficit in a prefrontal cortical system that underlies source memory.