Resting-state connectivity changes underpinning ICDs identified

The presence of impulse control disorders (ICDs) is associated with reduced resting-state connectivity between part of the associative striatum and both associative and limbic cortical regions in patients with Parkinson’s disease (PD), a study suggests.

Previous functional magnetic resonance imaging studies have suggested that connectivity alterations during mental tasks in PD patients with ICDs occur in limbic cortical or striatal regions.

Researcher Nicolas Carriere (Université Lille Nord de France) and colleagues therefore anticipated similar resting-state findings in the 19 PD patients with ICDs who underwent functional magnetic resonance imaging in their study.

Instead, they found that these patients had significantly reduced connectivity between the left anterior putamen (associative striatum) and the inferior temporal gyrus (associative cortex) and the anterior cingulate (limbic cortex), relative to that in 17 PD patients without ICDs, who were matched for age, gender and disease duration.

“These findings could be the consequence of either increased striatal and extrastriatal dopaminergic denervation in patients with ICD-PD or a more global, basal dysfunction of the associative corticostriatal loops at rest”, write the researchers in Neurology.

“The latter dysfunction might give rise to an imbalance between reward integration and control mechanisms and thus account for the hyperactivity of the dopaminergic mesolimbic system identified in activation studies.”

With a less strict statistical threshold, the team also found that ICD PD patients had reduced connectivity between the left dorsal caudate and the left gyrus rectus and the middle frontal and inferior temporal gyrus; as well as between the left anterior putamen and the inferior frontal gyrus.

There was also reduced connectivity affecting the posterior putamen – to the inferior temporal gyrus, superior frontal gyrus, posterior cingulate and medial frontal gyrus on the left side and to the medial frontal gyrus, middle frontal gyrus and cingulate gyrus on the right side.

Patients with ICDs did not have any structural brain differences to those without ICDs. Of note, the researchers found no significant connectivity differences between patients without ICDs and 16 age- and gender-matched healthy controls, which they say could be partly because their patients were on dopamine treatment at the time of scanning.

This, they argue, reduces movement artefacts and increases the relevance of the study, because ICDs “are supposed to be a functional perturbation and are strongly associated with treatment use”.

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