Conclusions

These results demonstrate:

1. Visually evoked 30-70 Hz oscillations are typically associated with repetitive burst firing in a sub-set of cortical pyramidal cells.

2. These pyramidal cells are located in Layers II-III and make local and distal axonal connections.

3. The repetitive burst firing of these neurons is generated through intrinsic ionic mechanisms, involving the interaction of afterdepolarizing and after-hyperpolarizing potentials.

We propose that synchronized, gamma (30-70 Hz) frequency activity is generated in the cerebral cortex in response to depolarization of chattering cells by excitatory synaptic inputs as well as the interaction of chattering cells with one and another through axon collaterals. The extensive connections of layer II/III pyramidal cells may allow sub-groups of chattering cells to form ensembles based upon temporal interactions and synchronization. Each ensemble may represent distinct components of the visual scene, and synchronized ensembles may form and break in accordance with changes in the visual input.

Some additional questions that we would like to address:

1. What are the cellular mechanisms of chattering?

2. Where to chattering cells project?

3. How are chattering cells influenced by neuromodulatory substances and attentional/behavioral state?

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If you have any comments, please contact either David A. McCormick or Charles Gray.