Summary: A neural pathway that leads directly from the thalamus to the hypothalamus plays a critical role in processing tactile information, a new study reveals.
Touch plays an important role in social behavior. A kind gesture, a hug, a pat on the back strengthens our social relationships. But what happens in our brain as a result of touch?
In their latest study, published in the scientific journal Current biologyresearchers from the Institute of Biology at the Faculty of Science of Eötvös Loránd University have described the role of a new neural pathway in the brain.
Social behavior requires complex sensory inputs involving multiple senses, eg touch, sight, hearing, smell. Psychologists, but also instinctively the ordinary person, know the importance of touch, for example, the calming effect of hugs and caresses from our relatives and friends.
The physical contact of touch is also important in social relationships, think of the grooming behavior of monkeys or an appreciative pat on the back.
Neurobiologists have previously identified that information acquired through touch is relayed in the brain’s thalamus and becomes conscious in the cerebral cortex, but at the same time it has been suggested that the brain learns stimuli from our peers in a another way, since the pleasant sensation appears even without awareness.
In order to learn more about the mechanism of touch without consciousness, a study led by Árpád Dobolyi, professor at Eötvös Loránd University, was completed, in which Semmelweis University, the Institute of Experimental Medicine and the University from Heidelberg also participated. The first author was David Keller, doctoral student of Árpád Dobolyi.
During their research, they pointed out that the neural pathway leading directly from the thalamus to the hypothalamus plays an important role in processing tactile information, and that this pathway uses parathyroid hormone neuropeptide 2 (PTH2) as a neurotransmitter. .
In the future, their findings may contribute to the development of therapeutic agents that can aid in the development of social behaviors.
“Research has shown that tactile stimuli from conspecifics are processed in the brain differently from stimuli created by inanimate objects. The two pathways separate in the region of the thalamus.
“The brain mechanisms activated by the congeners also directly reach the hypothalamic regions responsible for triggering behavioral, hormonal and vegetative responses, as well as the feeling of reward” – said Árpád Dobolyi, head of research at the Department of Physiology and Neurobiology, ELTE Institute of Biology.
WHAT HAPPENS IN OUR BRAIN WHEN WE ARE AFFECTED?
The researchers modeled the social contact of female rats who were littermates. The hypothalamus, located in the lower part of the brain, below the thalamus, is the main center for the regulation of social behavior in rodents, since in this species the role of the cerebral cortex is not dominant. At the same time, the hypothalamus probably also plays a role in regulating instinctive behaviors in humans. However, it is not known how the information necessary for social behavior arrives in the hypothalamus.
According to the research hypothesis, the ascending sensory pathway carrying information about social touch reaches the hypothalamus from the thalamus without a relay in the cerebral cortex. This thalamo-hypothalamic neural pathway was previously unknown. At the same time, such input can directly trigger hormonal and autonomic changes controlled by the hypothalamus.
First, the researchers showed that neurons in a hitherto unknown area of the thalamus are selectively activated in response to social contact. Then, the activity of these neurons was experimentally increased or decreased using chemogenetic methods based on the transfer of viral genes.
These thalamic neurons have been found to facilitate friendly social interactions between experimental rats of the same sex, which involve direct, i.e. physical, contact. They then described the outputs of the studied thalamic nucleus and found that neurons from the nucleus project most to the anterior part of the hypothalamus, the so-called preoptic area.
AFTER DISCOVERING NEURAL PATHWAYS, THEY TURNED TO MOLECULAR MECHANISMS
The researchers further proved that experimental manipulation of the activity of the thalamo-hypothalamic neural pathway also determines how well animals interact with each other. This neural pathway therefore plays an important role in the processing of information associated with contact. After that, the information-carrying molecules in the neural pathway, the so-called neurotransmitters, were examined. Neuropeptide transmitters play multiple roles in the neural networks responsible for social relations.
Oxytocin is a prosocial neuropeptide known to promote social interactions, including social contact in rodents.
Other neuropeptides have been shown to play crucial roles in the behavioral response to chronic social isolation.
The parathormone-like neuropeptide (PTH2) has recently been shown to sense the presence of conspecifics in zebrafish via mechanoreceptors in the lateral line organ. Surprisingly, the PTH2 neuropeptide was only present in thalamus neurons that were activated during social interaction.
Moreover, the level of PTH2 in these neurons decreased when the animals were separated from each other. In other experiments, the researchers showed that PTH2 stimulates neurons located in the preoptic area of the hypothalamus. However, when PTH2 was experimentally prevented from binding to its receptors in the preoptic area, physical contact between animals ceased.
This proved that the peptide neurotransmitter PTH2 transmits important inputs determining social behavior to the preoptic area from the thalamus. Finally, the researchers showed a similarity in the anatomical structure of the thalamo-hypothalamic neural pathway and the distribution of the PTH2 receptor between rat and human brains.
“This finding could also be important in the future for the treatment of psychological illnesses, as the avoidance of physical contact is an integral part of many illnesses. If we know these neural pathways and mechanisms, in the long term we can better understand why the avoidance of physical contact develops, and possibly prevent these processes and influence them favorably for the individual.
Of course, this is still a distant future, but with research we have come closer to understanding how our brain and therefore our body react to touch, which areas of the brain are activated when we are touched”, Árpád Dobolyi, head of research at the Department of Physiology and Neurobiology at the ELTE Institute of Biology summarized the findings.
About this social neuroscience research news
Author: Sara Bohm
Contact: Sara Bohm – ETLE
Image: Image is in public domain
Original research: Access closed.
“A thalamo-preoptic pathway promotes social grooming in rodents” by Árpád Dobolyi. Current biology
A thalamo-preoptic pathway promotes social grooming in rodents
- Social interaction increases activity in the posterior thalamus (PIL)
- Activity of socially tagged PIL neurons drives social grooming behavior
- PIL neurons expressing PTH2-neuropeptide project to the preoptic area (MPOA)
- PTH2 neurons excite MPOA cells and in turn control social grooming
Social contact is an essential component of communication. Little is known about the underlying pathways and mechanisms. Here, we discovered a new neural pathway from the posterior intralaminar thalamic nucleus (PIL) to the medial preoptic area (MPOA) involved in the control of social grooming.
We found that PIL and MPOA neurons were naturally activated by physical contact between female rats and also by chemogenetic stimulation of PIL neurons. Activity-dependent labeling of PIL neurons was performed in rats with physical social contact.
Chemogenetic activation of these neurons increased social grooming between familiar rats, as did selective activation of the PIL-MPOA pathway. Neurons projecting from PIL to MPOA express parathyroid hormone neuropeptide 2 (PTH2), and central infusion of its receptor antagonist decreased social grooming.
Finally, we showed a similarity in the anatomical organization of the PIL and the distribution of the PTH2 receptor in the MPOA between rat and human brain. We propose that the neural pathway discovered facilitates physical contact with conspecifics.
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