Purpose. To study whether adaptation and masking in cat VI result from the same cellular mechanism. Both adaptation and masking result in a reduction in the response to a test stimulus caused by an additional stimulus. In adaptation the additional stimulus is presented just prior to the the test stimulus. In masking the additional stimulus is presented concurrently with the test stimulus. Since they are accompanied by a loss of contrast sensitivity, these phenomena have been ascribed to a divisive contrast gain control mechanism. Methods. We measured the membrane potential responses of VI simple cells, while recording intracellularly with the whole-cell patch clamp technique from barbiturate anesthetized cats [Ferster & Jagadeesh, J. Neurosci., 1992]. The test stimuli were drifting gratings of preferred orientation and spatial frequency. Adaptation was studied by measuring the effect of preceding the test gratings with prolonged exposure to adapting gratings of different contrasts. Masking was studied by measuring the effect of adding to the test gratings mask gratings of different orientations. Results. Adaptation acts primarily by tonically hyperpolarizing the cells by up to 10 mV [Carandini & Ferster, Soc. Neurosci. Abstr., 1996]. In contrast, masking does not substantially hyperpolarize the cells. In addition, adaptation and masking have different effects on the membrane potential modulation caused by the test stimulus. This membrane potential modulation can be substantially reduced in size by masking, but is largely unaffected by adaptation. Conclusions. Adaptation and masking result from different cellular mechanisms. Adaptation is due to a largely subtractive mechanism, such as a decrease in tonic excitation received by the cells. Masking is due to a largely divisive mechanism that reduces the size of the visually driven inputs received by the cells. While different, these two mechanisms have similar effects on the gain of the firing rate responses of simple cells.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Dec 1 1997|
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