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There doesn't seem to be any region in the brain that is truly and only uni-sensory.

Many neurons in the cat and monkey deep SC are uni-sensory.

SIV neurons are excited almost exclusively by somatosensory stimuli.

SIV neurons' activity can be inhibited by activity in the auditory FAES.

The function of SIV is unknown.

Dehner et al. speculate that the inhibitory influence of FAES activity on SIV activity is connected to modality-specific attention: According to that hypothesis, an auditory stimulus which leads to strong FAES activity will suppress activity in FAES and thus block out cortical somatosensory input to the SC.

Very few perceptions are truly affected only by sensation through one sensory modality.

The most important cortical input to the SC (in cats) comes from layer V cortical neurons from a number of sub-regions of the anterior ectosylvian sulcus (AES):

  • anterior ectosylvian visual area (AEV)
  • the auditory field of AES (FAES)
  • and the fourth somatosensory area (SIV)

These populations in themselves are uni-sensory.

Colonius' and Diederich's explanation for uni-sensory neurons in the deep SC has a few weaknesses: First, they model the input spiking activity for both the target and the non-target case as Poisson distributed. This is a problem, because the input spiking activity is really a function of the target distance from the center of the RF. Second, they explicitly model the probability of the visibility of a target to be independent of the probability of its audibility.

My explanation for different responsiveness to the individual modalities in SC neurons: They do causal inference/model selection. different neurons coding for the same point in space specialize in different stimulus (strength) combinations.

This is basically, what Anastasio and Patton's model does (except that it does not seem to make sense to me that they use the SOM's spatial organization to represent different sensory combinations).