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Mental disorders

Depression and Manic Depression

Alzheimer’s-type Dementia

Chercheur : The groundbreaking findings of Yvette I. Sheline

Brain imaging studies have shown that patients suffering from depression have the same patterns of brain activity as schizophrenics who have negative symptoms (that is, who are introverted and apathetic rather than eccentric and agitated). The parts of the brain that are less active in both diseases (such as the frontal lobes) are the ones recognized as making people feel that they are in control of their own actions.

Similarly, both paranoid schizophrenics and people in the manic phase of bipolar disorder display hyperactivity in the prefrontal cortex. In the former group, this hyperactivity is expressed as a tendency to draw connections between things and events but to give these connections a hostile connotation. In the latter group, the connections have more of a euphoric effect.


In general, several regions of the brain are less active in people who are depressed than in people who are feeling in top form. The reduced activity in these areas probably explains why depressed people experience feelings of lethargy and exhaustion.

But major depression does not represent a malfunction in a single part of the brain. It is more likely due to a variety of brain abnormalities.

In depressed patients, some parts of the brain may display abnormally low activity, but others may be hyperactive. The important point is that depression sets in when the interactions among these various regions of the brain are interrupted or the equilibrium among them is upset.

Studies on brain activity in depressed people do, however, seem to reveal an overall pattern: a general decline in activity in the cortex, and especially the prefrontal cortex, combined with increased activity in the brain's limbic structures.


Prefrontal cortex (blue) and limbic system (red)

Scientists believe that the prefrontal cortex may act as a kind of brake that keeps emotional responses in check. When this brake becomes less effective, it might therefore give freer rein to negative emotions arising from the limbic structures, which are generally hyperactive in patients with depression or bipolar disorder. Antidepressant medications tend to reverse this pattern, increasing activity in the cortex while reducing hyperactivity in the limbic system.

Certain parts of the parietal lobe and of the superior portion of the temporal lobe are associated with attentiveness to the outside world. These parts of the brain work more slowly in people with depression, which confirms the observation that people with depression are constantly focused inward on their own dark thoughts.

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