| Research Abstract |
To elucidate spatial and cognitive function of the septo (SP)-hippocampal (HF) system, neural activity was recorded from alert monkeys during performance of a place-dependent conditional go-nogo task (PCA) task in which response/reinforcement contingencies of given objects were conditional upon the location of a motorized, movable device (cab) containing a monkey, and during the place-independent go-nogo tasks which required no conditional discrimination. Of 329 HF neurons recorded, the activity of 88 increased or decreased significantly in response to the presentation of an object during the PCA task. Responses of 17 neurons depended differentially on specific combinations of object, place and behavior only in the PCA task (specific-combination neurons). Responses of 12 ncurons responded differentially to the objects only in the PCA task (object-differential neurons). Characteristics of the 2 neuron types suggest that HF neurons encode both stimulus percept and attributes such as the
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place where the stimulus is presented, and the conditional relation imposed in the task. These results might be neurophysiological bases of episodic memory, and suggest thet there is linkage between spatial and non-spatial functions in the HF.Of 430 SP neurons recorded, the responses during the place phase in the 4 places were significantly different in 58 neurons. Responses of 8 of these neurons were also place-differential during the object phase as well as the place phase. Of 91 neurons responding differentially during the object phase, 43 responded differentially only in the PCA task, 19 and 2 neurons were related to the reward/nonreward and go/nogo contingencies, respectively. The results suggest that the SP is involved in integrating spatial information, conditional place-object relations, and reward/nonreward contingency.
In the non-invasive study, generators of monkey somatosensory evoked potentials (SEPs) in monkeys and visual evoked potentials (VEPs) in humans were investigated by dipole tracing (DT) method with 3-dimensional reconstructed real head model, which can equates surface potential distributions to a corresponding equivalent dipole. The results indicated sequcential movement of dipoles from the thalamus to area 5 via the SI area, and topographic localization of the dipoles around the calcarine fissures which were well comparable to the retinotopy in the occipital lobe. The functional MRI of brains of awake rats during transient whole brain ischemia indicated that the post-ischemic hyperemia which lasts 1 hr was significantly correlated to delayd neuronal death in the CA1 subfield of the HF,and those of a rat brain during licking of glucose solution indicated increase in signal intensity in the hypothalamus. Less
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