They describe how sensory information is transmitted between the brain hemispheres

The brain has a very special way of processing information from the sense of touch. Stimuli perceived on the left side of the body are processed in the right hemisphere of the brain and vice versa. This is a well-known problem, but how the two hemispheres share this information has not been described in detail.

Researchers from the laboratory directed by Ramon Reig At the Institute of Neurosciences (IN), a joint center of the CSIC and the Miguel Hernández University of Elche, have carried out work that has confirmed through physiological studies that a double representation between hemispheres allows interruptions between both sides of the body.

The study, published in the journal Scientific advancesdeals with a hypothesis known as Midline fusion theory (Fusion theory or midline unification). This theory, postulated in 1989 based on anatomical observations, found that the areas of the brain that encode sensory information near the midline of the body sent large numbers of connections that crossed to the other hemisphere.

So far the presence of these Axonsbut in researchers have demonstrated in mice the functional properties of those axons that cross and synapse with the other hemisphere. In particular, these connect tactile information from the midlines and produce an identical representation or activation of the information on both sides, allowing sensory information to be processed continuously.

They used the mouse whisker system because they are excellent tactile receptors that allow very precise stimulation of both the lateral and midline areas of the brain.

To conduct this study, the authors used the system of mouse clips, whiskers, Since these rigid hairs are excellent tactile receptors that allow it to stimulate both lateral areas and the midline areas with great precision. In addition, it is possible to observe in detail which part of the hemisphere responds to the stimulus.

The team verified that when a particular whisker on the mouse’s snout is stimulated near the midline (in the middle), the opposite hemisphere responds exactly the same. This explains how the brain can create this tactile spatial continuity between both sides of the body.

Thanks to the neuron recording technique used (In vivo patch clamp), also confirmed that when the tactile response occurs, in the opposite hemisphere (ipsilateral to the tactile stimulation) by the Neurons That crosses the corpus callosum, not only receiving the response that causes the neurons to be activated, but a few milliseconds later it also receives the inhibition needed to control the response.

The correct excitation-inhibition balance of neurons is essential for the normal development of brain activity A prolonged state of excitement would trigger an epileptic brain.

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sensory center

In this work, the first author of which is Roberto Montanarihave managed to accurately describe the complete circuit that communicates to both hemispheres of the brain: the information perceived in response to a sensory stimulus Row A (Rowa). Therefore, they represent a sensory center for interhemispheric communication.

In addition, they have confirmed that the information is transmitted via a specific track. The cerebral cortex, which encodes the mouse’s tactile information, is divided into rows and columns, each containing groups of neurons called “barrels.”

The work shows that communication between the hemispheres takes place in row A: “It is what is called heterotopic projection. For example, the barrels of row E hardly project to the row E of the other hemisphere, but do so through row A,” explains the director of the laboratory of sensory-motor processing in subcortical areas of the in Ramón Reig, and he adds that he adds, This is very interesting because the midline whisker receptors are located exactly in row A.

The experiments used a common anesthetic (lidocaine) to block all information coming from one side of the mouse’s snout to see what happened when the animal could only process sensory information from one side. Once again, they checked that the information passes through line A and connects both hemispheres.

The dorsolateral striatum not only receives tactile information but processes bilateral tactile information from both hemispheres.

To validate these results, the team recreated what they had done at the sensory level in mice using optogenetic techniques. The experiment consisted of Stimulate the cerebral cortex directly with light to observe the response of the neurons in rows A, and indeed they observed that the response coincided and produced the same phenomenon.

Coordinated and precise response

In this study, the authors found that the dorsolateral striatum not only receives tactile information but also processes tactile information from both hemispheres bilaterally.

The lab led by Reig studies the striatum to understand how the neurons in this brain region integrate sensory and motor information to create a coordinated and precise response. Problems in the functioning of this nucleus are linked to motor disorders such as Parkinson’s disease. This new research also details the route that bilateral tactile information follows before reaching the striatum.

This work was possible thanks to funding from the Ministry of Innovation, Science and Universities, the CSIC Severo Ochoa Excellence program of the Institute of Neuroscience, La Caixa and the ACIF program of the Generalitat Valenciana.

reference:

Montanari, R et al. “Callosal inputs generate side-invariant receptive fields in barrel cortex.” Scientific advancesinst (2023).

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