| Co-Investigator(Kenkyū-buntansha) |
TABUCHI Eiichi Toyama Medical and Pharmaceutical University, Graduate School of Medicine, Associate professor, 医学系研究科, 助教授 (70272911)
UMENO Katsumi Toyama Medical and Pharmaceutical University, Graduate School of Medicine, Assistant professor, 医学系研究科, 助手 (90086596)
HORI Etsuro Toyama Medical and Pharmaceutical University, Graduate School of Medicine, Assistant professor, 医学系研究科, 助手 (90313600)
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| Research Abstract |
1.In the present study, a role of the limbic system, especially the hippocampal formation (HF), in behavioral manifestation based on an interaction between the brain and environment was analyzed. We hypothesized that the HF encode environmental information in sequence
2.First, to investigate effects of distal environmental cues on place-related activity of the monkey HF neurons, 228 neurons were recorded from the monkey HF during virtual navigation by manipulating a joystick in a similar situation to a rodent water maze, where distal cues were important to locate the animal's position. Of these, 72 neurons displayed place-related activity in one or more virtual spaces. Most place-related responses disappeared or changed their spatial tuning (i.e., remapping) in the different virtual spaces with different arrangements of the distal cues. These specific features of the monkey HF might underlie neurophysiological bases of the human episodic memory.
2.To investigate a hippocampal (HF) involv
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ement in encoding and retrieval of overlapping sequences in episodic memory, rat CA1 neurons were recorded during a conditional delayed stimulus-response association task. A trial was initiated by a conditioned tone (CT) presented from one of 3 directions (right, left, and anteriorly). After a delay, one of the 3 different compounds consisting of 2 serial reinforcements and a delay (D) [i.e., aversive sensory stimulation (air puff, AP)-D-tube protrusion (TP) near an animal's mouth to evoke licking sucrose solution, TP-D-TP, and TP-D-AP] was presented. The 3 CT directions were associated with these 3 compounds in one-to-one correspondence, and its association was conditional upon the task conditions specified by the CT frequencies (300, 530, and 1200 Hz). Thus, in each task condition, the rats experienced the 2 reinforcement situations for the same AP and 4 reinforcement situations for the same TP. Of 111 CA1 neurons, 107 were identified as putative pyramidal neurons based on physiological parameters. These responses to the AP and TP were analyzed by 2-way ANOVA (task condition x reinforcement situation). Of 42 AP-responsive and 64 TP-responsive neurons, 36 and 53 displayed significant main effects and/or significant interaction, respectively. Furthermore, neural responses during the delay periods were dependent on the task conditions. The results demonstrated that majority of the HF neurons showed task condition-and/or reinforcement situation-dependent responses, suggesting a crucial role of the HF in representation of overlapping serial events in episodic memory.
3.We investigated human event-related potentials (ERPs) in a sound-sequence discrimination task in which subjects of different ages were required to encode and retrieve the temporal associations between sound stimuli. The results suggest that medial temporal lobe including the HF is an essential region for memory of sequential order in humans, and may contribute to age-related memory deficits in encoding and retrieval of associations between experiences.
4.To examine coherent activity across different brain areas, EEGs were analyzed by power spectrum and coherence analyses. The subjects were required to perform 3 tasks ; 1)raising their heels alternatively along with beep sounds (task 1, control task), 2)imagery of jogging while raising their heels along with beep sounds (task 2), 3)jogging imagery along with beep sounds (task 3). Mean θ power increased in the task 3, compared with the task 1, at most electrodes except for Fp1, Fp2, O1 and O2. Mean α power increased in the tasks 2 and 3 at most electrodes. Mean β power increased in the task 3 at Fz, C4, C5 and Cz. Mean coherence in θ, α and β-bands among the parietal, temporal, and posterior frontal electrodes significantly increased in the tasks 2 and 3. Furthermore, combinations of the electrodes with significant coherence in the task 3 were very similar to those of the task 2. The results suggest that a wide-scale neuronal network based on θ, α and β-band oscillation was formed among the areas related to motor, spatial cognition and object recognition during imagery of navigation. Less
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