Probing the dynamics of cortical microcircuits
For many years cortical columns have been thought of as feedforward multilayer elementary operational units (OPUN) of cortex. Yet, both anatomical and physiological evidence contradict this concept. Specifically, each pyramidal cell receives approximately 10,000 synaptic inputs, of which about 75% are excitatory; the vast majority of these excitatory inputs arise from other cortical neurons which result in a strong intra-cortical recurrent connectivity with a relatively weak input from subcortical structures. Interposed between this recurrent excitatory-network of pyramidal cells are a large variety of GABAergic inhibitory interneurons strongly interconnected with projection neurons. Accumulating evidence suggests that OPUN may actually be instantiated in such recurrent Excitation-Inhibition (E-I) circuits, in which information related to sensors or effectors is processed in a highly non-linear (e.g. strong feedback) fashion and is shaped by the strong neuromodulatory activity of the ascending diffuse systems. This microcircuit architecture is not specific to any specific sensory area, but it has instead been evident anywhere it has been sought after, including the primary motor and premotor cortices in all studied mammals.
My group research goal is to probe into the functional principles of such microcircuits by studying both feedforward activity induced by sensory or electrical stimulation and neuromodulatory activity that appears to change proportionally both the excitatory and inhibitory conductances.
We are using VSDi which permits recording of activity of whole neuronal populations with high spatio-temporal resolution. We augment our observations with a battery of methods including electrophysiological recordings, MR imaging, histology and electrical stimulation of thalamus and/or modulatory subcortical nuclei, such as the locus Coeruleus and Nucleus basalis.