The Cerebral Cortex Operates Through a Balance of Excitation and Inhibition:
The cerebral cortex exhibits multiple states of activity and excitability. Some of these states slowly change, such as the transition between sleep and waking. Others are more rapid, such as the operation of short-term or "working" memory and shifts in attention. Although we have a relatively clear understanding of how the slow changes in neuronal excitability may come about with the sleep wake cycle (e.g. through the release of neuromodulatory substances), it has been less clear how rapid changes of excitability may be generated. One hypothesis for the mechanisms underlying these rapid changes is through network dynamics: the rapid turning on or off (activation or deactivation) of groups of neurons. This type of persistent "reverberating" activity within networks of cortical neurons has been hypothesized to underlie short term or working memory (see next slide).
In this seminar, we examine the mechanisms by which local cortical circuits may rapidly change states of activity through balanced recurrent excitation and inhibition. To be Specific, by examining the properties of the UP and DOWN states of the slow oscillation in vitro, we sought to answer the following questions:
- What are the cellular mechanisms for the generation of persistent activity in the cortex?
How do synaptic barrages affect the excitability and responsiveness of cortical cells?
How does the activation of afferent inputs turn persistent activity on or off?