John Lisman
Wednesday 12th February 2014
Time: 4pm
Basement Seminar Room
Alexandra House, 17 Queen Square, London, WC1N 3AR
Oscillations: An organizational principle of Brain Function
Oscillations in the brain are now being studied by a large variety of methods, have been observed in most brain regions and have been implicated in a variety of processes. Yet, a substantial fraction of the neuroscience community does not think oscillations are fundamental to brain function. I will argue that oscillations are fundamental to the operation of sensory, memory and motor systems. This argument is based on the following: 1) That the question of which cells in a network fire can only be understood once one takes into consideration the fact that inhibition is oscillatory (at gamma frequency). Importantly, the rule that determines which cells fire is not cell autonomous (cannot be determined by the inhibitory and excitatory input to that cell), but depends on the entire network, which produces a type of winner-take-all computation. 2) Oscillations at different frequencies interact, the best example being theta and gamma frequency oscillations. The resulting theta-gamma code organizes multi-item messages. Each item is represented by an ensemble of cells that show synchronized firing during a gamma cycle. This code is now clearly demonstrated in the hippocampal region and its target structures (PFC and striatum). However, I will present evidence that it is also relevant to sensory processes. Notably, odors are represented in the olfactory bulb by a discrete temporal sequence that occurs during a sniff. This sequence is organized by gamma oscillations. I will present a model of how this sequence can be converted to a spatial pattern appropriate for recognition by an attractor network. 3) Although much less studied, there are indications that the motor system is also organized by oscillatory processes. I will review evidence that motor control is not continuous, but rather involves commands that occur at about 10Hz.