Monday, March 7, 2005

Dr. Paul Miller

 Brandeis University

  "Memory systems in the brain: modeling short-term and long-term processes"

2:00 pm in room P-149

Abstract:  Out thought processes require memory on a range of timescales. I will describe two projects in this talk, the first based on long-term memory, the second involving short-term (working) memory. (1) Long-term  memory is primarily based on the changes in the strength of connections between neurons at the synapses. It requires a transient event to cause a lasting change in the synaptic strength. I will describe a biochemical "switch" based on bistability of a kinase-phosphatase reaction scheme which models this process. Since only a small number (ten to thirty) of the enzymes involved are present in the small compartment, the post-synaptic density, where the reactions take place, and since the enzymes are replaced randomly on a daily basis, a crucial question arises as to the stability to fluctuations of any of the states of this "switch". We have investigated this stability numerically and analytically. (2) I will describe a network of neurons that models a  discrimination process requiring short-term memory. The model network uses integral feedback control to provide a response to a second stimulus that depends on an earlier stimulus. The behavior of neurons in the model network can explain some of the behavior of neurons recorded in the prefrontal cortex of monkeys while they perform such a sequential discrimination task.