Washington, August 12 : A study on monkeys suggests that the brain region involved in hearing can directly improve perception in the brain region involved in seeing, without the assistance of other structures to integrate the senses.
P. Barone and colleagues at the Centre for Brain and Cognition Research in Toulouse, France, recorded the neuronal responses with microelectrodes inserted directly into the primary visual cortex of a rhesus macaque, which was then required to orient its gaze towards a visual stimulus.
The researchers recorded the time taken for the neurons in the visual cortex to respond to the stimulus, or latency.
They later measured the latency when the visual stimulus was accompanied by a sound emanating from the same spot.
Barone says that the auditory stimulus did not affect latency when the visual signal was strong, but latency decreased by five to ten per cent when the visual signal was weaker.
The researcher said that that observations suggested that in some way the auditory stimulus speeds up the response to the visual stimulus.
"Our findings show that single neurons from one primary sensory cortex can integrate information from another sensory modality," claim Barone and colleagues.
The researchers propose that the auditory cue is processed more quickly than the visual stimulus, and because the monkeys have learned to associate that sound and sight, the visual cortex is primed to perceive the weaker signal.
"Our results argue against a strict hierarchical model of sensory integration in the brain and that integration of multiple senses should be added to the list of functions of the primary visual cortex," say the researchers.
The study has been published in the online open access journal BMC Neuroscience.