Compulsions - not a 'breakdown of control'? An unexpected conclusion

Compulsive behaviours - from compulsive handwashing to repetitive betting or drinking - are usually explained by a "habit loop": they say the habit becomes stronger than self-control, and it's as if the person is acting on autopilot. But a new study by the University of Technology Sydney (UTS) on rats offers an unexpected alternative: in some cases, compulsivity may be associated not with a lack of, but with excessive (albeit inappropriate) conscious control.

What the scientists tested

A team led by neuroscientist Laura Bradfield decided to test a popular hypothesis based on neuroimaging data: people with compulsive disorders often show signs of inflammation in the striatum, an area of the brain important for choosing actions. In the experiment, the researchers "simulated" such a condition in rats: lipopolysaccharide (LPS) was injected into the posterior dorsomedial striatum, causing a local neuroinflammatory response, and watched how this changed the balance between habitual and goal-directed behaviour.

The main result: not habit, but "too much purpose"

The expectation was that inflammation would reinforce habits - that is, behaviour would become more automatic. However, the opposite turned out to be true: the intervention caused the animals to retain and even increase goal-directed control where habit would normally "kick in" over time. The authors describe this as a shift to overly goal-directed control.

Next, the researchers tried to understand which cells might be behind the effect. Immunohistochemistry indicated the involvement of astrocytes (glia cells): there was evidence of their active changes/proliferation. To test for a causal role, the team chemogenetically affected Gi signalling in astrocytes in the striatum - this changed the activity of neighbouring neurons (medium spiny neurons) and affected how the animals controlled actions.

Why this is important for understanding compulsions

The authors draw a cautious conclusion: if the results are transferable to humans, then in striatum neuroinflammation, compulsive symptoms may be related not so much to "falling into a habit" as to maladaptively enhanced conscious choice of actions (as if the brain is constantly trying to "overcontrol" the situation). This, they argue, may explain some of the compulsive behaviours that don't fit neatly into the classic 'habit hypothesis'.

What's up with treatment

The text of the study discusses that approaches aimed at reducing neuroinflammation and at the mechanisms of astrocyte function may be promising avenues. But this is not a ready-made recommendation for patients: the work was done in animals and requires further testing.