Adaptation shifts preferred orientation of tuning curve in the mouse visual cortex.

In frontalized mammals it has been demonstrated that adaptation produces shift of the peak of the orientation tuning curve of neuron following frequent or lengthier presentation of a non-preferred stimulus. Depending on the duration of adaptation the shift is attractive (toward the adapter) or repulsive (away from the adapter). Mouse exhibits a salt-and-pepper cortical organization of orientation maps, hence this species may respond differently to adaptation. To examine this question, we determined the effect of twelve minutes of adaptation to one particular orientation on neuronal orientation tuning curves in V1 of anesthetized mice. Multi-unit activity of neurons in V1 was recorded in a conventional fashion. Cells were stimulated with sine-wave drifting gratings whose orientation tilted in steps. Results revealed that similarly to cats and monkeys, majority of cells shifted their optimal orientation in the direction of the adapter while a small proportion exhibited a repulsive shift. Moreover, initially untuned cells showing poor tuning curves reacted to adaptation by displaying sharp orientation selectivity. It seems that modification of the cellular property following adaptation is a general phenomenon observed in all mammals in spite of the different organization pattern of the visual cortex. This study is of pertinence to comprehend the mechanistic pathways of brain plasticity

Three examples of orientation shifts.

<p>From left to right (<b>A</b>) attractive, (<b>B</b>) repulsive and (<b>C</b>) no shift. Upper row: Raw data, error bars indicate SEM. Bottom row: Gaussian fits, same cells as in the upper row.</p

Comparative response modulations induced by adaptation.

<p>Upper row: repulsive shifts. Lower row: attractive shifts. Three responses are computed: Original preferred, responses to adapter, new preferred. Star indicates significant level p<0.05. Abbreviations, Ori: orientation, Ctrl: control, Adapt: adaptation</p

Distribution of orientation-class preference and shift magnitude significance.

<p>(<b>A</b>) Neurons divided into five orientation classes of 18°. Vertical and horizontal orientations dominate (that is cardinal orientations). (<b>B</b>) The relationship between shift-magnitude and significance level indicates that cardinal orientations have larger shift than cells whose orientation is oblique.</p

Typical example of an attractive shift.

<p>Twenty-five presentations of each orientation. Gaussian fits and orientation are normalized in this and other figures: optimal orientation is marked zero. Vertical broken lines indicate optimal orientations. Downward arrowhead indicates adapting orientation in this and all figures. Horizontal Right inserts show spike waveforms recorded during each phase of the recordings. Bar equals 1.6 ms.</p

Classification of cells after adaptation.

<p>Legend: UT: Untuned to Tuned, UU: Untuned to Untuned, TU: Tuned to Untuned.</p

Example of a neuron untuned to orientation.

<p>Prior to adaptation (in blue) no orientation evokes a stronger response. Following adaptation (in red) a clear optimal orientation emerges. Right inserts, tracing 1 and 2 show spike waveforms recorded during each phase of the recordings, bar equals 2.16 ms. Tracings in 3 illustrates PSTHs of evoked responses prior to (upper) and following (lower) adaptation respectively.</p