DOPAMINERGIC MODULATION OF WORKING-MEMORY FOR SPATIAL BUT NOT OBJECT CUES IN NORMAL HUMANS

It appears that functionally segregated visual pathways exist in the p rimate brain for the processing of visuospatial versus nonspatial info rmation. Functional segregation has been demonstrated for the early as sociative processing of sensory information but may also exist at high er levels of cognitive analysis. Namely, connections between the dorsa l visual system and dorsolateral prefrontal cortex (PFC) appear to med iate spatial working memory which is modulated by dopamine receptor fi elds in the principal sulcal region of the PFC, It is speculated that nonspatial working memory may be modulated within connections between ventral visual processing regions and the inferior convexity of the PF C. Whether dopamine facilitates nonspatial memory through connections between the ventral visual system and ventral PFC has not been examine d. In this study normal humans completed spatial and nonspatial workin g memory tasks under pharmacological challenges with a dopamine recept or agonist (bromocriptine) and antagonist (haloperidol) in a double-bl ind placebo-controlled repeated measures design. Findings indicated fa cilitation of spatial delayed working memory functions by bromocriptin e and impairment of spatial working memory functions by haloperidol. N either drug was effective in manipulating nonspatial memory performanc e. Control tasks were included to measure drug effects on basic sensor imotor and attentional processes. Findings suggest that separate proce ssing mechanisms for remembering ''what'' versus ''where'' an object i s may exist at structural, but also neurochemical, levels in the human brain.