Inhibitory Processing Remains Intact in Parkinson’s Patients, Study Suggests

The ability to block out irrelevant information when asked to recognize and name objects, known as inhibitory processing, remains intact in patients with Parkinson’s disease, a study has found.

The study, “The Suppression of Irrelevant Semantic Representations in Parkinson’s Disease,” was published in the journal Frontiers in Human Neuroscience.

Previous studies have shown that Parkinson’s disease might affect inhibitory processing in the brain. However, this is still a debatable subject in the scientific community, since the severity and type of impairments are highly varied among patients and studies.

“The lack of agreement concerning inhibitory processing in PD [Parkinson’s disease] is readily manifest in the literature concerning … the variety of lexical-semantic tasks including verbal fluency, semantic priming [saying words related to the prime word given, for example, wolf in reply to dog], and confrontation naming [naming a picture],” the researchers wrote in the study.

To study this, these researchers from the University of Queensland in Australia set out to investigate whether patients with Parkinson’s disease were able to block out inappropriate or irrelevant information when naming a picture.

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They used an object-based priming technique, in which participants were asked to name a red image and ignore a green image in a set of 144 superimposed images. The 144 images were then divided into three categories — identical, related and unrelated — containing 24 image pairs of primes (visual stimulus) and probes (patients’ choice).

“The green distractor image in the prime stimulus was identical to the red image in the subsequent probe stimulus in the identical condition [e.g. both representing a dog], semantically related to the red probe image in the related condition [e.g. both representing objects], or semantically unrelated in the unrelated condition [e.g. the green prime image showing an animal and the red probe image showing an object],” the researchers said.

The study enrolled 16 patients with Parkinson’s disease and 13 age-, sex- and education-matched healthy individuals used as controls.

Interestingly, both Parkinson’s patients and healthy controls took longer to name target images that were identical to the prime distractor image than they took to name target pictures that were unrelated to the distractor image. “This result suggests the presence of a negative priming effect across both groups,” the researchers wrote.

No significant differences in naming response time were found between related and unrelated image pairs in both groups. Likewise, no differences were observed in the magnitude of this negative priming effect in the two groups.

“The PD group performed similarly to controls across all conditions in terms of naming latency, demonstrating that the retrieval of an object’s name was slowed when that same item had previously been ignored,” the researchers wrote.

“These results suggest that inhibitory mechanisms related to the processing of visual-semantic stimuli may be largely intact in PD. Further investigation using paradigms that strictly control for the influence of lexical-semantic input and output is required in order to elucidate the integrity of such mechanisms,” they concluded.