WHO:	BCS Lunch Talk: Jozsef Fiser , BCS Postdoc
TOPIC:	Changing circuit dynamics underlie the emergence of sensory coding in developing visual cortex
ABSTRACT:	It is well known that in the absence of sensory input, spontaneous activity in both the developing and adult visual cortex has a highly coherent spatio-temporal structure. Before eye opening, this spatio-temporal structure has been suggested to play a crucial role in the formation of visual structures in the developing visual cortex. In contrast, after eye opening, spontaneous activity is traditionally viewed as noise that must be averaged out to obtain the true information encoded by visual neurons. We examined the idea that the ongoing activity, which is known to modulate cell responsiveness to sensory stimuli after eye opening significantly, is not noise but rather it plays a critical role in sensory processing. To this end, we assessed the impact of ongoing activity on the response of primary visual cortical neurons to dynamic natural-scenes and random noise displays in awake ferrets from the time of eye-opening to maturity. We found no dramatic changes in the ongoing cell activity immediately before and after eye opening that would support a very different role for spontaneous activity in those conditions. With respect to visually driven activity, the correspondence between evoked neural activity and the structure of the input signal was poor in immature animals, but systematically improved with age. However,this improvement was tightly linked to a gradual developmental shift in the dynamics of the ongoing activity. In addition, at all ages including the mature animal, the sensory input during visual stimulation produced only a small modulation of the ongoing correlations in neuronal firing present in the dark. Thus, in both the developing and mature visual cortex, sensory evoked neural activity in the primary visual cortex can be described as a modulation and triggering of the intrinsic circuit dynamics by the input signals, rather than as a direct code that itself mirrors the structure of the input signal. These results suggest that dynamic ongoing activity plays a significant role in visual cortical sensory coding.
WHEN:	2/4/2004 12:00:00 PM
WHERE:	Meliora 269

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