Abstract
Motor control is associated with suppression of oscillatory activity in alpha (8–12 Hz) and beta (12–30 Hz) ranges and elevation of oxygenated hemoglobin levels in motor-cortical areas. Aging leads to changes in oscillatory and hemodynamic brain activity and impairments in motor control. However, the relationship between age-related changes in motor control and brain activity is not yet fully understood. Therefore, this study aimed to investigate age-related and task-complexity-related changes in grip force control and the underlying oscillatory and hemodynamic activity. Sixteen younger [age (mean ± SD) = 25.4 ± 1.9, 20–30 years] and 16 older (age = 56.7 ± 4.7, 50–70 years) healthy men were asked to use a power grip to perform six trials each of easy and complex force tracking tasks (FTTs) with their right dominant hand in a randomized within-subject design. Grip force control was assessed using a sensor-based device. Brain activity in premotor and primary motor areas of both hemispheres was assessed by electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS). Older adults showed significantly higher inaccuracies and higher hemodynamic activity in both FTTs than did young adults. Correlations between grip force control owing to task complexity and beta activity were different in the contralateral premotor cortex (PMC) between younger and older adults. Collectively, these findings suggest that aging leads to impairment of grip force control and an increase in hemodynamic activity independent of task complexity. EEG beta oscillations may represent a task-specific neurophysiological marker for age-related decline in complex grip force control and its underlying compensation strategies. Further EEG-fNIRS studies are necessary to determine neurophysiological markers of dysfunctions underlying age-related motor disabilities for the improvement of individual diagnosis and therapeutic approaches.
Highlights
The ability to adapt our actions quickly to changes in the environment is a key function of human motor skills (Hermsdörfer et al, 2003)
One of the most sophisticated characteristics of fine motor skills is the precise grip force regulation according to the physical requirements of a manipulated object, which is necessary for the successful performance of various everyday activities (Hermsdörfer et al, 2003; Voelcker-Rehage and Alberts, 2005; Parry et al, 2019)
Functional activity in motor-cortical areas can be quantified as cerebral hemodynamics using brain imaging techniques such as functional magnetic resonance imaging and functional near-infrared spectroscopy or as electrical signals using the electroencephalography (EEG; Hamacher et al, 2015)
Summary
The ability to adapt our actions quickly to changes in the environment is a key function of human motor skills (Hermsdörfer et al, 2003). Previous studies have shown that oscillatory activity and cerebral hemodynamics are inversely related during the motor control process, that is, hemodynamic activity increases with a decrease in alpha and beta oscillations (Lachert et al, 2017). Changes in brain activity during the motor control process have been observed in various cerebral structures (Zaepffel et al, 2013), mainly in sensorimotor areas with a contralateral predominance (Taniguchi et al, 2000). Thereby, the SMA represents a key structure controlling the motor-cortical network while driving the regulation of grip forces by promoting and suppressing its activity (Grefkes et al, 2008a). According to previous studies, reduced inter-and intra-hemispheric connectivity between the SMA and the primary motor cortex (Grefkes et al, 2008b), upregulation of the parieto-frontal network activity in the stroke-lesioned hemisphere (Bönstrup et al, 2018), and pathological increases in beta oscillations (Rossiter et al, 2014a) were correlated significantly with motor deficits (Grefkes et al, 2008b; Rossiter et al, 2014a; Bönstrup et al, 2018)
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