Force related hemodynamic responses during execution and imagery of a hand grip task: A functional near infrared spectroscopy study

- Modulation of grip forces influences hemodynamic responses during the imagery and execution of a hand grip task.
- The imagery of the lower grip force results in a higher [oxy-Hb] increase compared to high grip force.
- The execution of a hand grip task at lower grip force leads to a delayed [oxy-Hb] increase.
- Differential fronto-parietal activation depending on force used in a hand grip task.

We examined force related hemodynamic changes during the performance of a motor execution (ME) and motor imagery (MI) task by means of multichannel functional near infrared spectroscopy (fNIRS). The hemodynamic responses of fourteen healthy participants were measured while they performed a hand grip execution or imagery task with low and high grip forces. We found an overall higher increase of [oxy-Hb] concentration changes during ME for both grip forces but with a delayed peak maximum for the lower grip force. During the MI task with lower grip force, the [oxy-Hb] level increases are stronger compared to the MI with higher grip force. The facilitation in performing MI with higher grip strength might thus indicate less inhibition of the actual motor act which could also explain the later increase onset of [oxy-Hb] in the ME task with the lower grip force. Our results suggest that execution and imagery of a hand grip task with high and low grip forces, leads to different cortical activation patterns. Since impaired control of grip forces during object manipulation in particular is one aspect of fine motor control deficits after stroke, our study will contribute to future rehabilitation programs enhancing patient's grip force control.