Researchers identify function of higher-order thalamus for the first time.


Every day, humans constantly absorb information through their sensory organs, which the brain then needs to process correctly. The information first reaches the thalamus and then travels to the cerebral cortex.  The thalamus is essentially the size of two walnuts and is located in the middle of the brain, all sensory perceptions converge here first. As the main relay center, it therefore needs to reconcile the flood of incoming information with the brain’s computing power.

It is known that the neurons in the so-called higher-order thalamus form the connecting lines between the thalamus and cerebral cortex.  However, their role in sensory processing is still unknown.  Now, a study from researchers at the Technical University of Munich (TUM) has shown for the first time in an animal model that these neurons enhance and temporarily store sensory information.  The opensource study is published in the journal Cell Reports.

Previous studies show that the higher-order thalamus consists of a class of thalamic nuclei defined by dominating input from the cortex.  The processes in the neurons at the transition point between the thalamus and the cortex are particularly interesting for neuroscientists.  However, very little is still known about the role and the effects of this region, described as the higher-order thalamus. Even though it is extremely important, as the neurons there develop contacts with numerous areas in the cortex and potentially affect these.  The current study, for the first time, depicts the neural activity in the sensory stimuli at this contact point in their experiments in the animal model.

The current study measured the processes in the neurons of the cortical target areas after the whiskers of sleeping mice had been touched at the same time each day.  The lab explain that the mouse’s whiskers are its most important sensory organ and the signals received by the whiskers are converted into sensations by the cortex.  They go on to note that the sensory system in mice, apes and humans is anatomically very similar.

Results show that the higher-order thalamus sends activating signals to the cortex, which were able to enhance cortical signals and maintain them even when the actual stimulus, touching the whiskers, no longer existed. Data findings show that the higher-order thalamus apparently serves to amplify important signals and also to store them temporarily over a certain period. The group conclude that the brain can thus filter out important information in the thalamus and then forward this information in an amplified form and for a longer period of time to the cortex.

The team surmise that their findings are applicable to many disciplines as information from the thalamus also affects behaviour as the cortex contains important areas relating to movement.  They go on to add that it appears that nature has created a general-purpose information processing system here. For the future, the researchers state that it is very useful for the global medical community as they can gain a lot of information in animal sensory-models, with a high probability that it will also apply to the human brain.

Source: Technical University of Munich (TUM)

 

The axons on the higher-order thalamus, which extend into the cortex, were highlighted with a (red) fluorescent protein in order to display the target areas in the cortex (red stripes in the top right of the photo). Only a small section of the brain is shown, and it is clear that a large number of cortical areas are affected. (Picture: R. Mease, M. Metz, A. Groh / Cell Reports, 10.1016/j.celrep.2015.12.026, modified, licensed under CC BY-NC-ND 4.0).

The axons on the higher-order thalamus, which extend into the cortex, were highlighted with a (red) fluorescent protein in order to display the target areas in the cortex (red stripes in the top right of the photo). Only a small section of the brain is shown, and it is clear that a large number of cortical areas are affected. (Picture: R. Mease, M. Metz, A. Groh / Cell Reports, 10.1016/j.celrep.2015.12.026, modified, licensed under CC BY-NC-ND 4.0).

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