The study, initiated by the Swiss researchers and published in Nature, constitutes ground-breaking work in exploring emotions in the brain.
Anxiety disorders constitute a complex family of pathologies affecting about 10% of adults. Patients suffering from such disorders fear certain situations or objects to exaggerated extents totally out of proportion to the real danger they present. The amygdala, a deep-brain structure, plays a key part in processing fear and anxiety. Its functioning can be disrupted by anxiety disorders.
Although researchers are well acquainted with the neurons of the amygdala and with the part those neurons play in expressing fear, their knowledge of the involvement of other regions of the brain remains limited. And yet, there can be no fear without sensory stimulation: before we become afraid, we hear, we see, we smell, we taste, or we feel something that triggers the fear. This sensory signal is, in particular, processed in the cortex, the largest region of the brain.
For the first time, these French and Swiss scientists have succeeded in visualising the path of a sensory stimulus in the brain during fear learning, and in identifying the underlying neuronal circuits.
What happens in the brain?
During the experiments conducted by the researchers, mice learnt to associate a sound with an unpleasant stimulus so that the sound itself became unpleasant for the animal.
The researchers used two-photon calcium imaging to visualise the activity of the neurons in the brain during this learning process. This imaging technique involves injecting a chemical indicator that is then absorbed by the neurons. When the neurons are stimulated, the calcium ions penetrate into the cells, where they increase the brightness of the indicator, which can then be detected under a scanning microscope.
Under normal conditions, the neurons of the auditory cortex are highly inhibited.
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INSERM (Institut national de la sant et de la recherche mdicale)