Auditory Motion Does Not Modulate Spiking Activity in the Middle Temporal and Medial Superior Temporal Visual Areas

Abstract

The integration of multiple sensory modalities is one of the key aspects of brain function, allowing animals to take advantage of concurrent sources of information to make more accurate perceptual judgments. For many years, it was thought that multisensory integration in the cerebral cortex only occurs in high-level "polysensory" association areas, but recent studies have demonstrated cross-modal influences in regions that were traditionally designated as unimodal. In particular, several human neuroimaging studies have reported that extrastriate areas involved in visual motion perception are also activated by auditory motion, and may integrate audio-visual motion cues. However, the exact nature and extent of the effects of auditory motion on the visual cortex have not been studied at the single neuron level. We recorded the spiking activity of neurons in the middle temporal (MT) and medial superior temporal (MST) areas of anesthetized marmoset monkeys upon presentation of unimodal stimuli (moving auditory or visual patterns), as well as bimodal stimuli (concurrent audio-visual motion). Despite robust, direction selective responses to visual motion, none of the sampled neurons responded to auditory motion stimuli. Moreover, concurrent moving auditory stimuli had no significant effect on the ability of single MT and MST neurons, or populations of simultaneously recorded neurons, to discriminate the direction of motion of visual stimuli (moving random dot patterns with varying levels of motion noise). Our findings suggest that MT and MST neurons do not process or integrate moving auditory cues.. CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under aThe copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/204529 doi: bioRxiv preprint first posted online 2 Significance StatementMany studies have demonstrated that brain regions originally thought to be unisensory may play a role in multisensory processing. For example, some neuroimaging studies have found activity in regions involved in the processing of visual motion can be modified by auditory motion, but this is controversial. We tested whether the spiking activity of neurons in two visual motion processing areas of the primate brain, areas MT and MST, can be modulated by moving auditory stimuli. Our results revealed that neurons in these areas neither respond to auditory motion, nor change their responses to visual motion according to auditory motion cues. These findings call into question the idea that audio-visual integration occurs at early stages of processing in the extrastriate cortex.

Shared Representation of Visual and Auditory Motion Directions in the Human Middle-Temporal Cortex

“…This would suggest that regions typically considered as purely unisensory may in fact show some level of abstraction by implementing canonical perceptual computations across the senses [16][17][18]. However, the idea that hMT + /V5 involves in motion processing other than for vision remains controversial and has notably been challenged by studies suggesting that the overlap between brain activity elicited by visual and non-visual motion is an artifactual byproduct of smoothing fMRI activity maps or by using group-level rather than individually defined hMT + /V5 [8,[10][11][12][19][20][21][22][23].…”

Do you hear what I see? How do early blind individuals experience object motion?

“…It has been suggested that hMT+ may be inherently multisensory, capable of representing auditory as well as visual motion signals [82]. However, auditory motion does not modulate spiking responses in marmoset MT/MST [83], and the majority of studies have failed to find auditory BOLD responses within individually localized hMT+ in sighted individuals [64,75,84] (although auditory motion responses are found in a nearby region [75]). One recent study did show successful classification of up–down versus left–right auditory motion in hMT+ in sighted individuals [85].…”