Document Detail


Grid alignment in entorhinal cortex.
MedLine Citation:
PMID:  22892761     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The spatial responses of many of the cells recorded in all layers of rodent medial entorhinal cortex (mEC) show mutually aligned grid patterns. Recent experimental findings have shown that grids can often be better described as elliptical rather than purely circular and that, beyond the mutual alignment of their grid axes, ellipses tend to also orient their long axis along preferred directions. Are grid alignment and ellipse orientation aspects of the same phenomenon? Does the grid alignment result from single-unit mechanisms or does it require network interactions? We address these issues by refining a single-unit adaptation model of grid formation, to describe specifically the spontaneous emergence of conjunctive grid-by-head-direction cells in layers III, V, and VI of mEC. We find that tight alignment can be produced by recurrent collateral interactions, but this requires head-direction (HD) modulation. Through a competitive learning process driven by spatial inputs, grid fields then form already aligned, and with randomly distributed spatial phases. In addition, we find that the self-organization process is influenced by any anisotropy in the behavior of the simulated rat. The common grid alignment often orients along preferred running directions (RDs), as induced in a square environment. When speed anisotropy is present in exploration behavior, the shape of individual grids is distorted toward an ellipsoid arrangement. Speed anisotropy orients the long ellipse axis along the fast direction. Speed anisotropy on its own also tends to align grids, even without collaterals, but the alignment is seen to be loose. Finally, the alignment of spatial grid fields in multiple environments shows that the network expresses the same set of grid fields across environments, modulo a coherent rotation and translation. Thus, an efficient metric encoding of space may emerge through spontaneous pattern formation at the single-unit level, but it is coherent, hence context-invariant, if aided by collateral interactions.
Authors:
Bailu Si; Emilio Kropff; Alessandro Treves
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-8-15
Journal Detail:
Title:  Biological cybernetics     Volume:  -     ISSN:  1432-0770     ISO Abbreviation:  Biol Cybern     Publication Date:  2012 Aug 
Date Detail:
Created Date:  2012-8-15     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7502533     Medline TA:  Biol Cybern     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Sector of Cognitive Neuroscience, International School for Advanced Studies, via Bonomea 265, 34136, Trieste, Italy, bailusi@sissa.it.
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