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Sheila Nirenberg; How neural systems adjust to different environments: an intriguing role for gap junction coupling. Journal of Vision 2009;9(8):24. doi: 10.1167/9.8.24.
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© ARVO (1962-2015); The Authors (2016-present)
The nervous system has an impressive ability to self-adjust - that is, as it moves from one environment to another, it can adjust itself 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. How the nervous system makes these shifts isn't clear. Here we show a case where 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 accompanies the switch from day to night vision. Our results show that the shift is produced by a mechanism in the retina - an increase in coupling among horizontal cells. Since coupling produces a shunt, the increase causes a substantial shunting of horizontal cell current, which effectively inactivates the cells. Since the cells play a critical role in shaping integration time (they provide feedback to photoreceptors that keeps integration time short), inactivating them causes integration time to become longer. Thus, a change in the coupling of horizontal cells serves as a mechanism to shift the visual system from short to long integration times. The results raise a new, and possibly generalizable idea: that a neural system can be shifted from one state to another by changing the coupling of one of its cell classes.
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