Possible role of dendritic compartmentalization in the spatial working memory circuit.
In spatial working memory tasks, pyramidal cells in the relevant cortical circuit receive massive inputs to shape stimulus location-selective sustained activity. A significant part of those inputs are applied onto the dendrites. Considering the dendritic morphology and circuit anatomy together with recently suggested branch-specific plasticity rules, external inputs transmitting the information of the stimulus location would be mapped onto some portion of the dendritic branches, rather than uniformly distributed over the branches. Meanwhile, recent studies revealed that each dendritic branch of pyramidal cell functions as a compartmentalized integration subunit through local spike generation and branch-specific excitation-inhibition interaction. I have examined how such nonlinear dendritic integration, combined with the nonuniform distribution of the external input, affects the behavior of the whole circuit by constructing a rate-coding model incorporating multiple dendritic branches of the individual pyramidal cell. Simulations varying the nature of dendritic nonlinearity and the configuration of somatically and dendritically mediated recurrent inhibition revealed that dendritic compartmentalization potentially enables the circuit to form an accurate memory depending on the contrast of the external input, but insensitively to its intensity, under certain conditions; in particular, when there exists tuned global dendritic recurrent inhibition or local dendritic inhibition coupled with global somatic inhibition. The model suggests that, when the circuit receives low-contrast or background input, only a small portion of dendritic branches of each pyramidal cell can overcome the local threshold so as to contribute to the somatic low-frequency firing, which in turn stabilizes the low-activity state of the circuit by recruiting recurrent inhibition.
Morita
Kenji
K
RIKEN Brain Science Institute, Hirosawa, Wako 351-0198, Japan. morita@brain.riken.jp
D000818:Animals; D001522:Behavior, Animal; D002540:Cerebral Cortex / Q000166:cytology; D003198:Computer Simulation; D003712:Dendrites / Q000502:physiology*; D000882:Haplorhini; D008570:Memory, Short-Term / Q000502:physiology*; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D016571:Neural Networks, Computer; D017711:Nonlinear Dynamics; D010775:Photic Stimulation / Q000379:methods; D017966:Pyramidal Cells / Q000166:cytology*; D013028:Space Perception / Q000502:physiology*