Chaire André Aisenstadt Chair 2007

The neural bases for various behaviors are thought to involve competing sub-populations of neurons.  Alternate actions are required for repetitive motor behavior such as respiration and locomotion and in executing the outcome of a decision-making task.  When visualizing an ambiguous scene  (such as the Necker cube) one may perceive ongoing temporal alternation between the possible interpretations. In binocular rivalry each eye views different images but perception alternates randomly between them, with a time scale of seconds.

Various dynamical models lead to alternating mutual exclusivity with neuronal competition implemented as reciprocal inhibition between neuronal populations.  Slow negative feedback sets the basic time scale for switching. We will describe two mechanistic frameworks for the switching behavior.  If the negative feedback is strong enough it can overcome dominance and alternations occur intrinsically and periodically. In an alternate, attractor-based, framework negative feedback is relatively weaker and alternations are induced by noise operating on a bistable system.  Concepts from dynamical systems are applied to understand the underlying mathematical structure.

Sound localization involves precise temporal processing by neurons in the auditory brain stem. The first neurons in the auditory pathway to receive input from both ears can distinguish interaural time differences (ITDs) in the sub-millisecond range.  These cells in the mammalian medial superior olive (MSO) have specialized biophysical features: two dendrites, each receiving input from only one side; very short membrane time constant (less than one ms);  specialized ionic channel properties, including a low-voltage activated potassium current, I-KLT.  This I-KLT contributes to phasic firing (one spike in response to a step of current), precise phase-locking, and extremely timing-sensitive coincidence detection.  We will describe the temporal feature-selecting properties of MSO cells based on biophysical (HH-like) modeling, in vitro (gerbil) electrophysiology and application of concepts from dynamical systems theory and coding theory.