Event Abstract

How neural systems adjust to different environments: an intriguing role for gap junction coupling

The brain has an impressive ability to self-adjust – that is, as it moves from one environment to another, it can adjust its information-gathering properties to accommodate the new conditions. For example, as it moves into an environment with new stimuli, it can shift its attention; if the stimuli are low contrast, it can adjust its contrast sensitivity; if the signal-to-noise ratio is low, it can change its spatial and temporal integration properties. These shifts are well described at the behavioral level – and are critical to our functioning – but the neural mechanisms that underlie them are not understood. How is it that a network can change its information-gathering properties on the fly?

Here we describe a case in which it was possible to obtain an answer. It's a simple case, but one of the best-known examples of a behavioral shift – the shift in visual integration time that occurs as an animal moves from a day to a night environment. During the day, when photons are abundant, the animal's visual system is biased toward short integration times. As night approaches, and photons become limited, the system shifts toward long integration times.

An intriguing hypothesis has emerged for how the shift takes place – it involves gap-junction coupling among the horizontal cells of the retina: It's well known that the coupling of these cells is determined by the light level in the environment. When the light level is high, the junctions close, and there's little coupling. When the light level drops, as it does at night, the junctions open, and extensive coupling ensues. Since coupling shunts current, the idea is that the extensive coupling causes a strong shunting of horizontal cell current, effectively taking the horizontal cells out of the system. Since horizontal cells are critical for shaping integration time – they provide feedback to photoreceptors that keeps integration time short – taking these cells out of the system makes integration time longer.

What makes the hypothesis intriguing is that it raises a new, and possibly generalizable idea – that a neural network can be shifted from one state to another by changing the gap-junction coupling of one of its cell classes. The coupling serves as a means to take a cell class out of the network and thus change the network's structure.

We tested this hypothesis for the case above using transgenic mice that cannot undergo horizontal cell coupling. They lack the horizontal cell gap-junction gene, and, as a result, their horizontal cells get locked into the uncoupled state. If the hypothesis is correct, these animals should not be able to undergo the shift to long integration times. The hypothesis held: the shift in integration time was blocked completely at the behavioral level, and almost completely at the physiological (i.e., ganglion cell) level.

In sum, we tracked a behavioral change down to the network that implements it. This revealed a new, simple, and possibly generalizable, mechanism for how networks can rapidly adjust themselves to changing demands.

Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009.

Presentation Type: Oral Presentation

Topic: Oral Presentations

Citation: Nirenberg S, Pandarinath C, Bomash I, Victor J and Tschetter W (2009). How neural systems adjust to different environments: an intriguing role for gap junction coupling. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.036

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Received: 30 Jan 2009; Published Online: 30 Jan 2009.

* Correspondence: Sheila Nirenberg, shn2010@med.cornell.edu

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