In a new study on rats, researchers have discovered brain circuits that may be linked to depression and schizophrenia. These brain circuits are responsible for the inability to feel pleasure.
Several human psychiatric disorders, such as schizophrenia and depression, have anhedonia as a core symptom. Anhedonia can be defined as inability to experience pleasure from activities that are normally found entertaining and satisfying. Currently there is no treatment for anhedonia, since not very much is known about the brain circuits that lead to it.
Previous studies have implied that anhedonia could be linked to the prefrontal cortex (PFC) – a brain region which covers the front part of the frontal lobe. Many authors have suggested that the functions of the prefrontal cortex are linked to an individual’s personality. The PFC has been implicated in personality expression, moderating social behaviour, planning complex cognitive behaviour, and decision making, according to scientists.
For the new study – published January 1 in the journal Science – the researchers conducted experiments on the rats’ medial prefrontal cortex. They looked at how a series of neurons reacted to dopamine (neurotransmitter that controls the brain’s reward and pleasure centres).
Using functional magnetic resonance imaging (fMRI), the researchers monitored the brain activity in rats. Whenever they shone light pulses on the rats’ brains, the dopamine circuits would activate.
The rats tended to socialize less when the researchers stimulated their medial prefrontal cortex with light. They also chose regular water over sugary water. According to the researchers, both of these responses are linked to anhedonia.
Based on brain imaging, the researchers found that when the medial prefrontal cortex was stimulated, it strengthened its connections with the ventral striatum and the orbitofrontal cortex (OFC), two brain regions which have been previously linked with responses to rewards; ventral striatum functions as part of the reward system.
Moreover, due to the stimulations of the medial prefrontal cortex, other brain regions became more isolated. These include the auditory cortex and the retrosplenial cortex (RSC), which may be related to schizophrenia and depression in humans, previous research has shown.
Dr. Karl Deisseroth, a neuroscientist and psychiatrist at Stanford University, said that in certain areas of the prefrontal cortex, elevations in excitability control the extent to which drives and rewards are compelling in (human) behaviour. To better understand how the brain work overall, as a coordinated system, further research needs to be conducted, according to Dr. Deisseroth.
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