----- Forwarded message from matti.weckstrom@oulu.fi ----- Date: Thu, 19 Nov 2009 11:57:39 +0200

Everybody is welcome to listen to the

Visiting lecturer Dr. Mikko Juusola from University of Sheffield, UK

who will talk about

Bottom-up and top-down processing of information in the Drosophila visual system.

The place: Anttilan Sali, Linnanmaa Time: Monday, November 23, 10.15 o'clock.

ABSTRACT

The small insect brain is often described as an input/output system that executes reflex-like behaviours that may vary because of noise.

The insect brain can also initiate neural activity and behaviors intrinsically, seen as spontaneous behaviors, different arousal states and sleep. However, little is known about how intrinsic activity in neural circuits affects sensory information processing in the insect brain and variability in behavior. Using a customised flight simulator system with targeted in vivo electrophysiology, we have now identified a relationship between Drosophila brain activity in the left and right optic lobes and spontaneous trial-to-trial variability in its behavioural choices when facing competing motion stimuli. In the experiments, when a Drosophila chooses one stimulus and attempts to orient toward it, the neural activity in the optic lobes is boosted on the chosen side and suppressed on the opposite side, although visual input to its eyes remains unchanged during this behavior. These results, therefore, show that intrinsic neural mechanisms gate visual information processing within the optic lobes, revealing possible neural correlates for "intending" (increase in activity) and "ignoring" (reduction in activity) in the Drosophila brain. In addition to establishing a functional and behavioral significance of intrinsic brain activity in selective orientation of Drosophila, these results offer new insight into the sources of variability in insect behavior.

Here, they suggest that the Drosophila brain may operate on its own, intrinsically, when choosing between competing stimuli, with external factors modifying, through accumulation of evidence, rather than determining the resulting behavior. The act of decision making would then rely upon a dynamic equilibrium between current inputs and past experiences, and the motivational state of the fly.

I will also briefly present our latest results about how adaptation at several synaptic connections within the retinal network improves neural encoding of changing information, and how the retinal information processing can be influenced by top-down signalling.

Matti Weckstrom MD PhD professor of biophysics Department of Physics University of Oulu PO Box 3000 90014 Oulun yliopisto, Finland phone (office) +358-8-553 1125 mobile +358-40-5561 422 email: matti.weckstrom@oulu.fi

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