| Research Abstract |
It is important to understand the brain mechanisms underlying memory and cognition from cellular events to individual behaviors. Toward this objective, the present project aims to investigate the mechanisms of top-down memory control (Hasegawa et al Science 281, 814-818, 1998) combining (1)single cell recordings of neuronal activity and (2) functional magnetic resonance imaging (fMRl), using animal models with macaque monkeys.
(1) We conducted single unit recording from inferior temporal cortex in partial split-brain monkeys. We have shown that activity of inferior temporal neurons during memory recall can be induced by top-down signals from prefrontal cortex in the absence of bottom-up signals (Nature 401, 699-703. 1999). We also have recorded activity of prefrontal neurons during oculomotor tasks, and found that prefrontal neurons can code spatial memory information to guide behavior, even when non-spatial cues instruct switch of the target location (Soc. Neurosci. Abstr. 26, 404. 2, 2000).
(2) We have built fMRl systems for scanning macaque monkeys using 1.5T and 4.7T magnets. With 1.5T magnet, we have shown the feasibility of fMRl to reveal somatotopy in primary and second somatosensory cortex (Eur. J. Neurosci. 11, 4451-56, 1999). With 4.7T magnet we have been making high-contrast activation maps of cortical oculomor areas (Soc. Neurosci. Abstr. 27, 345. 12, 2001). In future, we plan to make functional activation maps with cognitive memory tasks, with the aid of which we will perform functional inactivation and single unit experiments
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