Page 43 - UMH Sapiens 38

Science for Sapiens A year in research (2024)

esearchers from the Institute for Neuros- Researchers have
ciences (IN), a joint center of the University
Miguel Hernández (UMH) of Elche and the managed to describe in a
Spanish National Research (CSIC), have precise way the complete
carried out a study that has confirmed, in a
pioneering way, through physiological stu- circuit that communicates
dies, that there is a double representation both brain hemispheres
Rbetween hemispheres, which enables the
perception of continuity, without interruptions between both
sides of the body. The work has been published in the journal
Science Advances.

The study carried out by researchers from the Sensory-Mo-
tor Processing in Subcortical Areas laboratory, led by Ramon In this work, whose first author is Roberto Montanari, the re-
Reig at the Institute for Neurosciences (IN), addresses a hypo- searchers have managed to describe in a precise way the
thesis known as Midline Fusion Theory (fusion theory or uni- complete circuit that communicates both brain hemispheres:
fication of the midline). the information perceived before a sensory stimulus travels
through the callous body and is specifically processed in a
The brain has a very concrete way of processing information very specific region of the primary somatosensory cortex, in
from the sense of touch. Stimuli felt on the left side of the the mouse the barrels of row A (RowA). Therefore, these repre-
body are processed in the right brain hemisphere and vice sent a sensory center for interhemispheric communication.
versa. This is widely known, but until now it had not been
described in detail how the two hemispheres share this in- In addition, they have verified that the information travels
formation. through a specific “lane”. The brain cortex that encodes the
mouse’s tactile information is divided into rows and colum-
The Midline Fusion Theory was postulated in 1989 and, ba- ns, each of which contains groups of neurons called barrels.
sed on anatomical observations, established that the areas The researchers have found that communication between
of the brain that encode sensory information near the midli- hemispheres occurs in row A, “It is what is called heterotopic
ne of the body sent large numbers of connections that cros- projection. For example, the barrels of row E barely project
sed into the other hemisphere. So far, the presence of these to row E of the other hemisphere, but do so mostly through
axons had been observed, but IN researchers have proven row A”, Ramon Reig explains, and adds that this is very inte-
the functional properties of those axons that cross and sy- resting because it is precisely in row A where the receptors
napse with the other hemisphere in mice. These especially of the whiskers of the middle line are located. Experts used a
connect tactile information from the parts of the midline and common anesthetic agent (lidocaine) to block all information
generate an identical representation or activation of the infor- coming from one side of the nose of the mouse to check what
mation on both sides, enabling continuous sensory informa- happened when the animal could only process the informa-
tion processing. tion on one side. Once again, they found that the information
travels through row A connecting both hemispheres.
To carry out this study, the researchers have used the system
of the whiskers of the mouse, since these rigid hairs are tacti- To validate these results, the researchers imitated what they
le receptors that enable stimulating with great precision both had done at the sensory level in mouse whiskers using op-
the lateral zones and the zones of the midline, in addition, it togenetics techniques. The experiment consisted of directly
is possible to observe in detail which part of the hemisphere stimulating the brain cortex with light to observe the respon-
responds to the stimulus. Experts were able to see that when se of neurons in rows A and, indeed, they observed that the
a certain whisker of the nose of the mouse is stimulated near response coincided and gave rise to the same phenomenon.
the midline (at the center of the same), a response occurs
at a given contralateral location, and one-third of neurons The researchers have found that the dorsolateral striatum
in the homologous region of the opposite hemisphere also both receives tactile information and also processes bilateral
respond exactly the same. This explains how the brain can tactile information from both hemispheres. Reig’s laboratory
generate that tactile spatial continuity between both sides of at the IN studies striatum to learn how neurons in this brain
the body. region integrate sensory and motor information to produce
a coordinated and accurate response. Problems in the func-
Furthermore, thanks to the technique of registering neurons tion of this nucleus are related to motor disorders such as
used (in vivo patch-clamp), the researchers also found that, Parkinson’s disease. This new research also accurately des-
when the tactile response occurs, in the opposite hemisphere cribes the path that bilateral tactile information follows befo-
(ipsilateral to tactile stimulation), through neurons that cross re reaching the striatum core region.
the corpus callosum, it receives the response that causes the
activation of neurons, and also, a few milliseconds later, re- This work has been possible thanks to the funding of the Mi-
ceives the inhibition needed to control the response. The co- nistry of Innovation, Science and Universities, the CSIC Seve-
rrect excitation-inhibition balance of neurons is essential for ro Ochoa Excellence Programme of the Institute for Neuros-
the brain to develop its activity normally since a continuous ciences, La Caixa, and the ACIF Programme of the Generalitat
state of excitation would trigger an epileptic brain. Valenciana.

43