Study Finds No Differences in Cognitive Abilities Between Sexes

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by Steve Bryson, PhD |

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No differences in cognitive abilities were identified between men and women with Parkinson’s disease, according to a recent study.

Although no tests were conducted, the researchers suggested the lack of cognitive differences between male and female patients, which is found in aging healthy individuals, may be due to the loss of a protective effect of estrogen among the women.

“The mechanism of the protective effect of estrogen on cognitive function remains unclear, and further studies are needed,” the scientists wrote.

The study, “The Impact of Sex on the Neurocognitive Functions of Patients with Parkinson’s Disease,” was published in the journal Brain Sciences.

People with Parkinson’s disease can experience motor symptoms such as tremors, slow movements, and muscle rigidity, but also non-motor symptoms, including cognitive impairment, depression, and sleep problems.

The prevalence of Parkinson’s disease increases with age and is higher in men. Some studies suggest there are no sex-specific differences in cognitive function among Parkinson’s patients. However, others indicate that male patients have a lower global cognitive function in the early stages of the disease, and more mild cognitive impairment, while women patients have worse cognitive function overall.

The discrepancies between these studies may be due to differences in the assessment tools or variations in the patients’ disease stage. Also, a lack of healthy controls can make it difficult to determine whether cognitive changes are related to the disease or sex.

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To further investigate the impact of sex on the cognitive function of Parkinson’s patients, researchers based at the National Cheng Kung University in Taiwan designed a study to evaluate cognitive function using a wide range of assessment tools in both healthy controls and patients across different disease stages.

In addition, the team explored the relationship between cognitive function and clinical characteristics, including the age of onset, disease duration, and medication dose in patients of each sex.

A total of 60 male and 34 female Parkinson’s patients were recruited, along with a group of 53 healthy men and 114 women as controls. Researchers investigated six cognitive domains: executive function (cognitive control), memory, mental processing speed, visual-spatial ability, attention, and language.

First, they compared differences between those with and without Parkinson’s to understand the cognitive deficits created by the disease.

Compared to controls, Parkinson’s patients scored significantly worse in executive function as assessed by the Modified Wisconsin Card Sorting Test, Category Fluency, and the Stroop Color and Word Test (SCWT). Scores for mental processing speed also were significantly lower, as determined by Digit Symbol Substitution and Symbol Search.

Visual-spatial ability was affected with patients reporting lower scores in Pentagon Copying and the scaled score of Block Design. Also, the raw score of Logical Memory was worse for patients than controls.

Next, the team focused on differences in cognitive function due to sex among patients and controls.

Among the control group, men had significantly more years of education than women. After adjusting for years of education, female controls had higher scores for executive function based on the Category Fluency and the word and color scores of SCWT. The raw scores for Logical Memory were higher in women, as were scores for delayed recall.

In contrast, overall, there were no differences in cognitive function between men and women with Parkinson’s.

Further comparison with male controls found male patients performed worse on the Color Trails Test part A and Digit Symbol Substitution, “indicating a worse processing speed in male patients,” the team wrote.

Among female participants, Parkinson’s patients performed worse than controls on the category score of Modified Wisconsin Card Sorting Test, Digit Symbol Substitution, and Pentagon Copying, “indicating worse executive function, processing speed, and visuospatial ability in female patients,” they added.

Finally, researchers examined the relationship between clinical characteristics and cognitive function in male and female patients.

After adjusting for age and years of education, disease stage as determined by the Hoehn and Yahr scale could predict the performance of working memory and mental processing speed in male Parkinson’s patients.

In comparison, the team found no significant associations between the clinical characteristics and cognitive function in female patients.

“The present study found a differential effect of sex on the neurocognitive function of healthy aging and [Parkinson’s disease] population,” the authors concluded.

“The poor performance of both male and female patients with [Parkinson’s disease] in neurocognitive function tests and the disappearance of the sex difference, which is present in the healthy aging population, in patients with [Parkinson’s disease] suggest a gradual loss of the neuroprotective effect of estrogen after the initiation of the neurodegenerative process,” the authors suggested.

However, “the lack of accurate biological markers representing the estrogen level limits the extrapolation of the neuroprotective effect of estrogen on cognition in the female healthy aging group,” they wrote.

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