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2016 ; 11
(9
): e0162640
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Dynamic Organization of Hierarchical Memories
#MMPMID27618549
Kurikawa T
; Kaneko K
PLoS One
2016[]; 11
(9
): e0162640
PMID27618549
show ga
In the brain, external objects are categorized in a hierarchical way. Although it
is widely accepted that objects are represented as static attractors in neural
state space, this view does not take account interaction between intrinsic neural
dynamics and external input, which is essential to understand how neural system
responds to inputs. Indeed, structured spontaneous neural activity without
external inputs is known to exist, and its relationship with evoked activities is
discussed. Then, how categorical representation is embedded into the spontaneous
and evoked activities has to be uncovered. To address this question, we studied
bifurcation process with increasing input after hierarchically clustered
associative memories are learned. We found a "dynamic categorization"; neural
activity without input wanders globally over the state space including all
memories. Then with the increase of input strength, diffuse representation of
higher category exhibits transitions to focused ones specific to each object. The
hierarchy of memories is embedded in the transition probability from one memory
to another during the spontaneous dynamics. With increased input strength, neural
activity wanders over a narrower state space including a smaller set of memories,
showing more specific category or memory corresponding to the applied input.
Moreover, such coarse-to-fine transitions are also observed temporally during
transient process under constant input, which agrees with experimental findings
in the temporal cortex. These results suggest the hierarchy emerging through
interaction with an external input underlies hierarchy during transient process,
as well as in the spontaneous activity.
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