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Title: Sensory induced long-lasting modification of spontaneous activity in the somatosensory cortex : electrophysiological and modelling studies
Author: Phoka, Elena
ISNI:       0000 0004 2723 8326
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Emerging evidence suggests that spontaneous neocortical activity is not merely noise but can be modulated and/or engaged by sensory stimulation. We examined whether naturalistic sensory stimulation can induce specific long-term changes in spontaneous cortical state dynamics in the mouse somatosensory cortex, using both in vivo electrophysiology and modelling. Repetitive, high-frequency multi-whisker stimulation using sandpaper resulted in spontaneous ring rate increase of layer IV and Vb multi-units. The ring rate increase in these layers was sustained for at least 25 minutes following the stimulus. The ring rate increase was accompanied by an increase in layer IV sink amplitude. Increase in spontaneous activity was found also in excitatory single-units in layers IV and Vb. Neither the depth of anaesthesia nor stimulus-induced desynchronization could account for this effect. Finally, we found that elimination of lateral inputs, achieved by trimming away all but the principal whisker, abolished the effect. Single-whisker stimulation resulted in a decrease of activity in layers II/III, IV, Vb and VI, and was accompanied by a decrease in layer IV sink amplitude. In parallel, to study whether Spike-Timing-Dependent-Plasticity (STDP) can explain modifications in spontaneous synaptic dynamics, we developed a biologically inspired large-scale model of rodent barrel layers II, III and IV. Our model consists of approximately 4000 spiking neurons, 1.7 million synapses and 2.2 million dynamical variables. Repetitive sensory stimulation induced long-lasting changes in synaptic weights. The initial state of the network, described by a spontaneous attractor, shifted to a post-stimulus stable state following several repetitions of the same structured stimulation pattern. Furthermore, we found that STDP mediated modifications enabled our network to distinguish between structured and shuffled stimuli. Our experimental and modelling results show that sensory experience induces long-term modification of spontaneous activity in the somatosensory cortex. They suggest that lateral projections and time-dependent plasticity mechanisms play an important role in this process.
Supervisor: Schultz, Simon ; Barahona, Mauricio Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral