American scientists clarified the role of the posterior parietal cortex in the pre-processing of visual stimuli. It turned out that the decrease in the activity of this part of the brain with low-frequency transcranial magnetic stimulation accelerates the reaction to the stimuli which blink at a low frequency. Article published in Scientific Reports.
For the processing of visual stimuli in the brain meets the eponymous part of the cortex is visual, and it is divided into several parts. All information that enters the brain through sight, initially processed in the primary visual cortex (also called V1): then, depending on which aspect of the stimulus need to be processed (shape, color, or orientation), the information sent to other departments.
However, before the primary visual cortex will begin its work, preprocessing of the stimulus performs the posterior parietal cortex and it is responsible for the pre-processing of other sensory stimuli. In a recent work, the researchers even proposed to include this area in the somatosensory system of the brain, based on structural pathology. About the role the posterior parietal cortex plays in the processing of visual stimuli, from the functional data obtained on humans, very little is known.
Seth Elkin-Frankston (Seth Elkin-Frankston) from Medical school at Boston University and his colleagues have used repetitive transcranial magnetic stimulation at low frequency (one Hertz) to study the work of the posterior parietal cortex. This stimulation is considered to be inhibitory, that is, the activity parcel when its impact is reduced.
Just experiment was attended by 36 volunteers. Each of them showed a screen on which over 100 milliseconds, there were a small dark spot Gabor: it could show inside the little square or in the first time window or the second. Between the Windows was a small break in 400 milliseconds, and the participants had to answer, in which window (first or second) they saw a spot with low or high frequency of flashing. The reaction time is started to count at the end of the second window (if it was possible to give an answer), and the test was performed before, immediately after and one hour after stimulation.
Scientists have found that when using spots with a low flashing frequency stimulation significantly (p = 0.03) reduced the reaction time is about 50 milliseconds: in other words, by reducing the activity of the cortex processing visual stimulus accelerated. On this basis, they concluded that the inhibition of the rear of the parietal lobe in the pre-processing of the visual stimulus actually affects its further processing, even without affecting the visual cortex.
Generally, the processing of visual stimuli can affect not only the primary stages of the process in the brain, but processing of a stimulus of another modality, and the distribution of attention: it’s not so long ago have shown scientists from the UK and Germany.