Abstract
Loss of one sensory modality can cause other types to become more perceptive (cross-modal plasticity). To test the hypothesis that the loss of vision changes the perceptual threshold in the somatosensory system, we applied optogenetics to directly manipulate the afferent inputs involved in the whisker-barrel system using a transgenic rat (W-TChR2V4) that expresses channelrhodopsin-2 (ChR2) selectively in the large mechanoreceptive neurons in the trigeminal ganglion (TG) and their peripheral nerve terminals. The licking behavior of W-TChR2V4 rat was conditioned to a blue LED light cue on the whisker area while the magnitude and duration of light pulses were varied. The perceptual threshold was thus quantitatively determined for each rat according to the relationship between the magnitude/duration of light and the reaction time between the LED light cue and the first licking event after it. We found that the perceptual threshold was more significantly reduced than the control non-deprived rats when the rats were visually deprived at postnatal 26–30 days (P26-30, early VD group), but not at P58-66 (late VD group). However, the sensory threshold of a late VD animal was similar to that of a control. Our results suggest the presence of cross-modal plasticity by which the loss of vision at the juvenile period increased the sensitivity of the somatosensory system involved in the touch of whiskers.
Highlights
Loss of one type of sensory modality can cause perceptual improvement of other sensory modalities
Three groups of the W-TChR2V4 rats were trained for a Go-task paradigm conditioned to the photostimulation on the whisker area: the early visual deprivation (VD) group in which the animals were visually deprived at P26-30, the late VD group in which the animals were visually deprived at P58-66, and the control group without VD (Fig 2A)
After training that consisted of the Go task for 0.5 h with an inter-trial-interval (ITI) of 20 ± 5 s (Fig 2C), a Go-task conditioning test was made with salient photostimulation (12.4 mW/mm2 for 50 ms)
Summary
Loss of one type of sensory modality can cause perceptual improvement of other sensory modalities. This process is called cross-modal plasticity [1,2]. The brain can adapt to sensory deprivation in one modality by increasing plasticity and retuning neuronal circuits in other remaining modalities. Cross-modal plasticity of different sensory systems may require a coordinated shift of attention from the deprived to the intact sense [3]. The perceptual threshold is the weakest stimulus that an animal can detect and create perception, and should be under the regulation of neural computation in the central nervous system (CNS). The loss of one modality may affect the threshold in the others.
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