They describe in a "pioneering" study how sensory information is transmitted between the hemispheres of the brain

VALENCIA, 30 Nov. (EUROPA PRESS) -

Researchers from the laboratory directed by Ramón Reig at the Institute of Neurosciences (IN) - a joint center of the Higher Council for Scientific Research (CSIC) and the Miguel Hernández University (UMH) of Elche - have carried out a study that has confirmed , "in a pioneering way", through physiological studies, that a double representation is produced between the hemispheres of the brain that allows the perception of continuity, without interruptions between both sides of the body.

And, according to the CSIC, the brain has a very specific way of processing information from the sense of touch. Stimuli felt on the left side of the body are processed in the right brain hemisphere and vice versa. This is a widely known issue, but until now it has not been described in detail how the two hemispheres share this information.

Now, this work, published in the journal 'Science Advances', addresses a hypothesis known as Midline Fusion Theory. This theory was postulated in 1989 and, based on anatomical observations, it established that the areas of the brain that encode sensory information close to the midline of the body sent a large number of connections that crossed to the other hemisphere.

Until now, the presence of these axons had been observed, but IN researchers have demonstrated in mice the functional properties of those axons that cross and synapse with the other hemisphere. These especially connect tactile information from the midline parts and generate an identical representation or activation of the information on both sides, allowing sensory information to be processed continuously.

To carry out this study, the researchers have used the mouse whisker system, since these rigid hairs are excellent tactile receptors that allow very precise stimulation of both the lateral areas and the midline areas and, in addition, It is possible to observe in detail which part of the hemisphere responds to the stimulus.

The experts were able to verify that when a certain whisker on the mouse's snout close to the midline (in the center of it) is stimulated, not only does a response occur in a specific contralateral location, but a third of the neurons in the homologous region from the opposite hemisphere respond exactly the same. This explains how the brain is able to generate that tactile spatial continuity between both sides of the body.

Furthermore, thanks to the neuron recording technique used (in vivo patch-clamp), the researchers also verified that, when the tactile response occurs, in the opposite hemisphere (ipsilateral to the tactile stimulation) through the neurons that cross the corpus callosum, it not only receives the response that causes the activation of the neurons, but, a few milliseconds later, it also receives the inhibition necessary to control the response. The correct balance of excitation-inhibition of neurons is essential for the brain to develop its activity normally, since a continuous state of excitation would trigger an epileptic brain.

In this work, whose first author is Roberto Montanari, they have managed to precisely describe the complete circuit that communicates both cerebral hemispheres: the information perceived by a sensory stimulus travels through the corpus callosum and is specifically processed in a very specific region of the brain. primary somatosensory cortex, in the mouse the barrels of row A (RowA). Therefore, these represent a sensory center for interhemispheric communication.

Furthermore, they have verified that information travels through a specific lane. The cerebral cortex that encodes the mouse's tactile information is divided into rows and columns, each containing groups of neurons called "barrels."

Researchers have proven that communication between hemispheres occurs in row A: "This is what is called heterotopic projection. For example, the barrels in row E barely project to row E of the other hemisphere, but do so through of row A", explains the director of the Laboratory of Sensory-Motor Processing in Subcortical Areas of the IN Ramón Reig, and adds that this is very interesting because it is precisely in row A where the midline whisker receptors are located. .

The experts used a common anesthetic (lidocaine) to block all information coming from one side of the mouse's snout in order to see what happened when the animal could only process sensory information from one side. Once again, they verified that the information travels through row A, connecting both hemispheres.

To validate these results, the researchers imitated what they had carried out, at a sensory level, in the mouse whiskers with optogenetic techniques. The experiment consisted of directly stimulating the cerebral cortex with light to observe the response of the neurons in rows A and, indeed, they observed that the response coincided and gave rise to the same phenomenon.

Researchers have discovered that the dorsolateral striatum not only receives tactile information, but also processes tactile information bilaterally, from both hemispheres. The laboratory directed by Reig at the IN studies the striatum to understand how the neurons in this brain region integrate sensory and motor information to produce a coordinated and precise response.

Problems in the function of this nucleus are related to motor disorders such as Parkinson's disease. This new research also precisely describes the route that bilateral tactile information follows before reaching the striatum.

This advance has been possible thanks to funding from the Ministry of Innovation, Science and Universities, the CSIC Severo Ochoa Excellence Program of the Institute of Neurosciences, la Caixa and the ACIF Program of the Generalitat Valenciana.