Does Hemispheric Asymmetry Reduction in Older Adults in Motor Cortex Reflect Compensation?

Area of Science:

• Cognitive Neuroscience
• Neuroimaging
• Aging Research

Background:

• Older adults often exhibit increased bilateral brain activation during sensorimotor tasks.
• The hemispheric asymmetry reduction in older adults (HAROLD) is a common finding, but its functional significance is debated.
• It is unclear if HAROLD represents a compensatory mechanism for age-related cognitive decline.

Purpose of the Study:

• To investigate whether the HAROLD effect in older adults is a compensatory mechanism for sensorimotor tasks.
• To differentiate between compensatory and non-compensatory explanations for age-related changes in brain activity asymmetry.
• To examine the relationship between ipsilateral brain activity and behavioral performance in aging.

Main Methods:

• Utilized functional magnetic resonance imaging (fMRI) in two independent studies with large adult lifespan samples (N=586 and N=81).
• Employed behavioral measures (reaction time) and multivariate Bayes (MVB) decoding to analyze brain activity patterns during right-hand finger responses.
• Compared univariate and multivariate analyses of motor cortex activation in relation to task performance.

Main Results:

• Standard analyses confirmed the HAROLD pattern in the motor cortex of older adults.
• Behavioral data showed no correlation between ipsilateral motor activity and task performance (reaction time).
• MVB decoding indicated that increased ipsilateral activity in older adults did not enhance action decoding and could even reduce it.

Conclusions:

• The findings contradict the compensatory hypothesis for HAROLD.
• Age-related ipsilateral hyperactivation in motor cortex appears nonspecific.
• Results support alternative hypotheses, such as reduced neural efficiency or impaired interhemispheric inhibition in aging.