Computational experiments support a competitive function in the the CA3 region of the hippocampus |
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Authors: | F Ventriglia |
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Institution: | (1) Istituto di Cibernetica, CNR, Via Toiano 6, 80072 Arco Felice (NA), Italy |
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Abstract: | The comprehension of activities and functions of complex brain structures requires, among other things, information on simultaneous
activities in several regions. Results reported in the literature using multi(micro/macro)electrode recordings or imaging
techniques provide incomplete information due either to the small size and/or small number of investigated regions or to the
poor spatiotemporal resolution, respectively. This is particularly true for the hippocampus and its subfields, and mathematical
modeling and computer simulation have been used with the aim of obtaining information when this is lacking. Global activities
in the CA3 field of the hippocampus, and in particular the genesis of theta rhythm and sharp waves, have been investigated
here by a mathematical model formulated within the frame of a kinetic theory of neural systems. The model has taken into account
data of experimental results both on different PSPs recorded in hippocampal neurons and on recurrent pyramidal collateral
geometries. The computational ‘experiments’ to which the model was subjected suggest that the sharp waves arise through a
selective and short block of the fast inhibitory neurons of CA3, produced by a medial septum inhibitory input, whereas the theta activity is produced by a durable,
continuous inhibition of the slow inhibitory neurons. Information obtained also suggests that the recurrent pyramidal collaterals subserve a competitive, rather
than a cooperative, organization. Based on these results a hypothesis on the possible functional organization of the CA3 field
and of the entire hippocampus has been formulated. According to this hypothesis, the CA3 imposes a serial order on the flow
of activity arriving at the hippocampus from the entorhinal cortex and from its connected polymodal cortical regions. This
ordering permits cortical activities, arriving at CA3 on appropriate time intervals, to produce effects in regions of brain
to which the CA3 projects. The competing cortical activities are lost. |
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Keywords: | |
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