“ Welcome to a new episode of 'How long does it really take?'Wearing a bathrobe and sunglasses, videographer Christine Newrutsen has made a name for herself on social media by filming and timing herself as she completes a task she's been putting off for weeks, months, or even years. Behind the banality of procrastination, which fuels the popularity of this content, lies a brain circuit that researchers have just succeeded in deactivating in macaques.
“ In everyday life, we are often faced with necessary but unpleasant tasks. Most of us are familiar with these kinds of situations: we know we must act, but something prevents us from taking the first step. Our results suggest that the pathway linking the ventral striatum to the ventral pallidum (VS-VP, two brain regions, editor's note) plays a role in this type of behavioral hesitation", explains to Science and Future Ken-Ichi Amemori, a biologist at Kyoto University (Japan), who led this research published in the journal Current Biology. “ In simple terms, this mechanism could be involved in phenomena such as avolition (a decrease in spontaneous motivation to act) and procrastination, which consists of postponing the moment of starting an unpleasant but necessary task.. »
Observing motivation in macaques
To observe the determinants of this "first step," researchers used a protocol called "approach-rejection." Facing a screen, two male macaques had to choose between two buttons to accept or reject a task presented to them from two types. Some tasks allowed direct access to a reward (a drink), while others first delivered unpleasant but painless bursts of air to the monkeys before the reward.
The number of times the user looks away at the very beginning of the task on the screen indicates their motivation, while choosing to refuse the task reflects an aversion. In our study, motivation is defined as the willingness to undertake a trial, which we measure based on the animal's engagement in the task before any choices are presented to it.“, confirms Ken-Ichi Amemori.
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Blocking a brain circuit restores motivation
To circumvent the macaques' lack of motivation, researchers are targeting the communication circuit between two brain regions involved in motivational regulation and reward processing: the ventral striatum and the ventral pallidum. Dysfunction of the former has been identified in severe depression. To disrupt this pathway, researchers are using chemogenetics, a technique that genetically modifies neurons in the macaques' ventral striatum so that they produce an inhibitory receptor.
When a compatible product is infused, the neurons drastically reduce their activity and almost completely cease communicating with the ventral pallidum. By cutting off this pathway, the result is clear! The macaques no longer hesitate; their motivation is restored. However, this has no impact on their decision to accept or refuse the task. This pathway appears to influence whether an action is initiated under negative or unpleasant conditions, regardless of how the brain assesses the attractiveness of the outcomes.", interprets Ken-Ichi Amemori. We therefore interpret this circuit as regulating motivational engagement in aversive contexts rather than as a mediator of anxiety or fear reactions per se. »
Restoring motivation in several psychiatric disorders
Avolition, or lack of motivation, is a source of suffering in several psychiatric conditions such as depression or schizophrenia. Patients continue to value positive outcomes but struggle to take action. Similar difficulties in taking action are also observed in neurological disorders such as Parkinson's disease, particularly in its early stages, when akinesia (difficulty initiating movement) is predominant.“, adds Ken-Ichi Amemori.
The team hopes that understanding the detailed mechanisms underlying motivation and the shift to action could explain the emergence of these symptoms and provide avenues for alleviating them. Potential avenues could lead to interventions such as deep brain stimulation, non-invasive neuromodulation (like transcranial magnetic stimulation, in which copper coils placed on the skull generate an electrical current), or even highly targeted pharmacological treatments, which are currently far from feasible.
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A necessary restraint, ethical considerations
But researchers warn that this must be done with caution, because this circuit, which acts as a brake on action, is useful and helps prevent exhaustion or burnout. If this circuit is oversuppressed, it could reduce adaptive caution and lead to risky or impulsive behaviors. Therefore, any potential therapeutic application should be considered with great care.“, supports Ken-Ichi Amemori. “ Any intervention that alters motivation raises important ethical questions, particularly regarding individual autonomy and the risk of social or institutional pressure to resort to such interventions.. »
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