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Olfactory information converges in the amygdaloid cortex via the piriform and entorhinal cortices: observations in the guinea pig isolated whole-brain preparation

Authors

  • Riichi Kajiwara,

    1. Neuroscience Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
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  • Takashi Tominaga,

    1. Department of Neurophysiology, Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan
    2. Laboratory for Dynamics of Emergent Intelligence, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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  • Ichiro Takashima

    1. Neuroscience Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
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Dr R. Kajiwara, as above.
E-mail: r.kajiwara@aist.go.jp

Abstract

The amygdaloid cortex (AC) has reciprocal connections with the entorhinal cortex (EC) and also receives projections from the olfactory bulb and the piriform cortex (PC). To assess the possibility that the AC and EC represent functionally coupled structures in the olfactory stream of information, we investigated the propagation pattern of neural activity in olfactory cortices − PC, AC and EC − using optical recordings with voltage-sensitive dyes in the guinea pig in vitro isolated whole-brain preparation. We observed two distinct pathways that convey neural activation evoked by olfactory nerve stimulation: a medial pathway from the PC to the AC, and a lateral pathway from the PC to the lateral EC along the rhinal sulcus. Besides being activated directly via the medial pathway, the AC was activated a second time via activity that propagated from the lateral EC. Lesion experiments revealed that the lateral pathway close to the rhinal sulcus is crucial for neural activation of the EC. Consistent with this activation pattern, we observed two separate, sharp downward deflections in field potential recordings, and we recorded synaptic potentials with multiple peaks from single neurons in the AC. Our findings suggest that the AC and EC are functionally coupled during olfactory information processing, and that this functional linkage may allow the AC to integrate olfactory sensation with information retained or processed in the EC.

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