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Michael R Ibbotson, Nicholas S Price, Colin W Clifford; Acceleration sensitivity and habituation in PMLS neurons. Journal of Vision 2003;3(9):409. doi: 10.1167/3.9.409.
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© ARVO (1962-2015); The Authors (2016-present)
The cat posteromedial lateral suprasylvian area is a cortical region implicated in the analysis of visual motion during locomotion. Its cells show a population preference for centrifugal motion. We have found that cell responses habituate to repetitive stimulation with constant speed stimuli. This is not consistent with PMLS's hypothesised role because sustained motion during locomotion would strongly attenuate responsiveness.
We tested PMLS neurons with moving sine-wave gratings using a range of constant accelerations or decelerations (0 to 5, 10 or 20 Hz in 0.5, 1 or 2s; 0.025–0.2cpd) and a range of constant velocity stimuli (0–25 Hz). The stimulus sequence was: stationary grating, moving, stationary, blank screen. The stationary and blank periods ranged from 0–10s, allowing the effects of adaptation and habituation to be studied. We found that in many cells with peripheral receptive fields, accelerating stimuli evoked much higher firing rates than constant velocity stimuli. This was the case for velocities throughout the entire range experienced during the accelerating phases. Repetitive velocity ramps separated by 0–1s rest periods did not cause the same level of habituation as repetitive stimulation by constant velocity stimuli. For constant velocity stimuli, response strength decreased rapidly over the first 4–8 presentations of a stimulus. Some cells responded more strongly to constant speed than to accelerating stimuli but still habituated to the former but not to the latter.
The responses suggest that some PMLS cells are better stimulated by novel stimuli such as speed changes. This is consistent with the region's purported role in locomotion analysis, since it could provide sensitivity to turning movements or objects moving against the background. Sensitivity to velocity changes could also explain how the cells continue to respond during locomotion, despite their rapid adaptation.
Procedures were approved by the ANU Animal Experimentation Ethics Committee.
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