How is depression diagnosed?

According to the DMS5 criteria (5th edition of the Diagnostic and Statistical Manual of Mental Disorders), depression is defined as a state of sadness or apathy (loss of desire and/or motivation).
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Diagnosis of depression

Ruminations are defined by an inability to “change one’s mind”; the patient remains “fixed” on the same negative thoughts.

Our emotions change over time. This may seem obvious, but understanding these variations precisely, their dynamics and the brain regions involved, is of major importance from a therapeutic perspective. Emotional variations are in fact a key feature in several mental health disorders such as depression. When we feel an emotion, there are two phases. First, there is the triggering of the emotion, which may be sudden or gradual – this is known as the ‘explosiveness’ of the emotion. Then there is the phase of compensating for the emotion, i.e. the intensification or attenuation of the emotion over time, assessed by its degree of “accumulation”.

The devaluation or ‘negative affect’ in self-perception is often modified, and perhaps even differently in people with suicidal tendencies. There is a correlation between self-perception and the level of depression.

These ‘negative affects’ are often accompanied by a lack of ‘positive affect’, which translates into an inability to experience pleasure, to have the will and to take action.

The most recent knowledge in neuroscience suggests that depression is a pathology of motivation, i.e. affecting the brain networks involved in decision-making and in evaluating the cost/benefit in relation to the effort to be made.

When we have to choose between several actions or decide to make an effort, our decision is based on the respective weight of two elements: the benefits, i.e. the reward we can obtain or the loss we can avoid, and the costs, in particular the effort required.

The origin of motivational disorders may lie either in a reduction in sensitivity to rewards or losses, or an increase in sensitivity to effort. These two mechanisms undoubtedly coexist in the same patient to varying degrees. A depressed patient, for example, may be unable to join friends for an outing, either because the reward, the pleasure of being with loved ones, is abolished, or because the cost of the actions required before going out, such as getting ready, getting dressed and going to the restaurant, is increased.


At the Paris Brain Institute

The “CIA: cognitive control – interoception – attention” team co-directed by Philippe FOSSATI and Liane SCHMIDT showed in 2017 that differences in the explosiveness of emotion triggering are linked to activity in the medial prefrontal cortex. This region is thought to be involved in self-perception. Here, its activation could therefore reflect the difference between the evaluation given by others and the participants’ idea of themselves. The differences in accumulation are linked to activation of the posterior part of the insula, a region known to play a key role in the integration of emotional signals. These results could have implications for the treatment of mental health disorders.

The ‘Motivation, brain and behaviour’ team, co-directed by Mathias PESSIGLIONE, Jean DAUNIZEAU and Sébastien BOURRET, is studying apathy and motivation from different angles. Dopaminergic and noradrenergic neurons play an important role in motivation. Thanks to a behavioural study, researchers have shown that dopaminergic neurons are involved in decision-making, while noradrenergic neurons contribute to mobilising the energy required for action.

This discovery is fundamental, as these two aspects of behaviour could be preferentially targeted in apathetic patients.

Recently, using intracerebral recordings, the same team identified 4 fundamental properties of the brain systems that determine our preferences. For further information

Bénédicte BATRANCOURT, an INSERM researcher in the “FRONTLAB: Functions and dysfunctions of frontal systems” team, directed by Richard LEVY, has led the ECOCAPTURE project, which measures the level of apathy in natural conditions and specifies its form.

Apathy is characterised by a loss of motivation, desire and emotions, and a deficit in the ability to perform and initiate useful behaviours.

It is the most common symptom observed in patients suffering from depression and Alzheimer’s and Parkinson’s diseases. Until now, little was known about this syndrome, it was poorly understood and its assessment was subjective.

This new, simple and objective measurement method paves the way for studies correlating the degree of apathy with the progression of neurological and psychiatric diseases, and for measuring the effect of treatments on this syndrome.