Ipsilateral premotor cortex complements complex finger movement in young but not in aging brains

2070 

Abstract Submission 

Gen Miura¹, Tomoyo Morita², Tomoya Furuta¹, Eiichi Naito²

¹Osaka University, Osaka, Japan, ²National Institute of Information and Communications Technology, Osaka, Japan

Gen Miura  
Osaka University
Osaka, Japan

Tomoyo Morita  
National Institute of Information and Communications Technology
Osaka, Japan

Tomoya Furuta  
Osaka University
Osaka, Japan

Eiichi Naito  
National Institute of Information and Communications Technology
Osaka, Japan

The human sensorimotor system is full of plasticity. The brain can recruit the sensorimotor cortices (dorsal premotor cortex [PMd], primary motor cortex [M1], primary somatosensory cortex [S1], and superior parietal cortex of Area 2) to control the ipsilateral hand. Ipsilateral sensorimotor activation can be seen when stroke patients (Lotze et al. 2006) and healthy older adults perform simple unimanual movement (Loibl et al. 2011) and even when healthy younger adults perform complex unimanual movement (Hutchinson et al. 2002). Although the clinical study suggests the importance of PMd for complementation of hand motor function among the ipsilateral cortices, it is unclear whether this is also the case in healthy younger and older adults. To address this question, we measured brain activity during simple and complex finger movements using functional magnetic resonance imaging (fMRI) in younger and older adults.

31 healthy right-handed young adults (YA group: 22.1 ± 1.8 years, 22 males) and 48 older adults (OA group: 71.1 ± 4.3 years; 31 males) participated in this study. Motor tasks were 1-Hz button pressing with the right index finger (Simple task) and 0.8-Hz stick rotation requiring coordination between the right thumb, index, and middle fingers (Complex task). Brain activity was measured during both tasks using fMRI. Functional images were collected using T2*-weighted gradient echo-planar imaging (EPI) with a 3.0-Tesla MRI scanner (Trio Tim; SIEMENS, Germany) and a 32-channel array coil for each participant. We first identified task-related brain activity. Since we are particularly interested in the sensorimotor cortices (PMd, M1, S1, and Area 2), we defined each of these regions as region-of-interest (ROI) in both hemispheres, and examined activation and deactivation in each ROI. Next, we examined if the ipsilateral sensorimotor activity emerges in relation to motor performance (= maximum number of stick rotations in 10 seconds) which was evaluated outside the MR scanner. Finally, we examined brain regions that enhanced functional coupling with each contralateral seed region (PMd, M1, S1, and Area 2) during the complex task as compared to the simple task by conducting a generalized psychophysiological interaction analysis. We investigated these points both in younger and older adults to elucidate differences between them. The study protocol was approved by the NICT Ethics Committee and the MRI Safety Committee of the CiNet (no. 2003260010). We explained the details of the present study to all participants before the experiment, and they then provided written informed consent. The study was conducted according to the principles and guidelines of the Declaration of Helsinki (1975).

In the YA group, the ipsilateral PMd, S1, Area 2 activated during the complex task, while the ipsilateral M1 remained deactivated as in the simple task. Ipsilateral PMd activity increased in individuals with poorer (less dexterous) performance (Figure 1). All of the contralateral seed regions consistently enhanced interhemispheric functional coupling with the ipsilateral PMd, which was just anterior to the ROI, during the complex task as compared to the simple task (Figure 2). In contrast, in the OA group, all the ipsilateral cortices including the M1 activated during the complex task, but none of the cortical activity showed performance-related change. Increase in functional connectivity within the contralateral cortices rather than between-hemispheric connectivity was observed during the complex task as compared to the simple task (Figure 2).

The results suggest the importance of ipsilateral PMd and its complementary role of motor function when healthy young adults perform complex finger movement. Even though ipsilateral sensorimotor activation can be seen in older adults, the aging brain seems not to use this interhemispheric strategy to complement hand motor function.

Aging ²

Motor Planning and Execution ¹

BOLD fMRI

Aging

Cortex

FUNCTIONAL MRI

Motor

Other - Complex motor control, Ipsilateral sensorimotor cortex