Cortical plasticity and neuronal assemblies in rat auditory cortex
Single neurons, acting alone, can not account for the complex and rapid computations that are routinely accomplished by the behaving nervous system. Recent studies with separable multi-neuron recordings are showing that neuronal assemblies can indeed be detected, and that their organization is very dynamic, depending on variables like time, physical stimulus and context. Various perturbations, both peripheral and central can affect aspects of assembly organization. This dissertation explores both single neuron and assembly properties in the rat's auditory cortex. Acoustic stimuli are used as a normal, physiological input, and weak electrical intracortical microstimulation (ICMS) as a perturbation that forces a rapid cortical reorganization. In this setting various aspects of neuronal interactions are changed by the ICMS. Multi-neuron recording of cortical activity under Ketamine differed from that under Nembutal, although in both situations we observed that cortical neurons were highly synchronous and exhibited oscillatory firing patterns. ICMS induced fast changes in the cortical map and in the receptive field properties of cells at the electrically stimulated and adjacent electrodes. ICMS also incremented afterdischarge responses. These consisted of an initial response to the auditory stimulus followed by less intense repetitive activity that was stimulus time locked and had a period of 8-12 Hz., similar to that of the spontaneous synchronous activity. Significant cross correlations between two spike trains depended on the anatomical distance between the two neurons. ICMS changed the strength but not the number of such correlations. Joint Peri-stimulus analysis and Gravity analysis showed that the correlation between neuronal activities varied over time. We have identified neuronal assemblies based both on their receptive field properties and on correlated firing. Close anatomical spacing between neurons was conducive to, but not sufficient for membership in the same assembly. ICMS changed cortical organization by altering assembly membership. Our data show that neuronal assemblies in the rat auditory cortex can be established transiently in time and that their membership is dynamic.
Maldonado, Pedro Esteban, "Cortical plasticity and neuronal assemblies in rat auditory cortex" (1993). Dissertations available from ProQuest. AAI9331817.