Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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BCCN Kolloquium

Wednesday, 24.05.2006 14 c.t.

Morphing approaches to these elusive neuronal attractors

by Prof. Dr. Alessandro Treves
from Cognitive Neuroscience Sector, SISSA, Trieste, Italy

Contact person: Fred Wolf

Location

Seminarraum Haus 2, 4. Stock (Bunsenstr.)

Abstract

Attractor dynamics is widely thought to underly the memory functions of the cortex, but the quest for convincing evidence is still ongoing. Focusing on memory representations in the hippocampus of rats and in the inferior temporal cortex of monkeys, we have tried to reveal the discrete transitions induced by attractors by proceeding slowly across the edge of putative attractor basins - with morphing paradigms. Recordings by Leutgeb et al in Trondheim, from the hippocampus of rats running in a box morphed between a familiar square and a familiar cylinder, showed a smooth interpolation of neural representations, despite the sharp transitions found in a similar experiment by Willis et al in London. Disappointing. Our computer simulations suggest some of the critical differences behind the discrepancy. In a HFSP collaboration with UCL (fMRI) and Seattle (neurophysiology), we have presented morphed visual stimuli to humans and monkeys. These intermediate stimuli tend to be perceived away from a priming endpoint, a visual aftereffect that fMRI localizes in anterior temporal cortices. Our network model, however, suggests that aftereffects have little to do with attractor states, and can result simply from firing rate adaptation. The neural activity elicited in monkeys by the morphed stimuli, on the other hand, indicates the existence of attractors: after a few tens of msec, neurons respond to all morphing levels that excite them with similar rates, while they respond with graded rates to morphing levels in the lower range.

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