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Functional Imaging and Robotics for Sensorimotor Transformation

Final Report Summary - FIRST (Functional Imaging and Robotics for Sensorimotor Transformation)

The ability to use the hand with skill and dexterity depends critically on the ability to use somatosensory information arising from sensory receptors in the skin and muscles. However, little is known about the neural mechanisms which transform somatosensory information into motor commands to control the finger forces and motions. The FIRST project was designed to address these deficiencies in our knowledge and to explore the effect of stroke on these mechanisms. A novel approach was developed in which functional brain imaging in the resting state was used to isolate the functional connections in the brain which are activated during the sensorimotor transformation.

The project focused on three somatosensory functions, tactile discrimination, tactile guidance and shape perception in the context of object manipulation. To elucidate the neural mechanisms involved in transforming somatosensory inputs into motor outputs a pioneering approach was employed in which changes in resting-state functional connectivity were induced by training subjects to perform novel tasks implemented on high-fidelity haptic devices. Participants in the study trained with one of three different haptic devices (Latero, Pantograph and Dual Pantograph) to perform a task requiring tactile discrimination, tactile guidance or shape perception while blindfolded. Without vision their movements had to be controlled entirely by their sense of touch (somatosensation). This isolated the brain regions involved in processing the touch sensations and transforming them into the muscle actions required to perform the task.

The Latero created sensory input by displacing the skin of the fingertip laterally by fractions of a millimeter. By modulating this displacement as the hand moved participants experienced a sensation of stroking a textured surface. The task tested the ability to recognize changes in texture. The Pantograph created sensory input by applying a small force to the fingertip. By modulating the force as the hand moved participants experienced a sensation of moving along the surface of a compliant object. The task tested the ability to move along the surface without losing contact. The Dual Pantograph created sensory input by applying a small force to the thumb and index finger. By modulating the direction of the force as the position of the thumb and finger changed participants experienced a sensation of trying to grasp an elliptical shape. The task tested the ability to find the widest part of the shape.

The resting-state technique employed in the FIRST study requires that the regions of interest in the brain are highly activated during the training task. A functional MRI scan which provides a measure of activity in the entire brain is then conducted immediately after the training while the individual rests in the scanner. The acquired resting-state brain activity is analyzed for functional connectivity. Functional connectivity is a measure of the correlation of activity between any two areas of the brain. If this measure changes significantly following training it indicates that the two areas were highly active in the task.

One of the main objectives of the project is to determine whether two brain areas which undergo a significant change in functional connectivity are involved in transforming somatosensory signals into signals which adjust muscle activity (sensorimotor transformation). The approach that we use is to identify features of the sensory input that trigger adjustments in finger movement or force. The ratio between the magnitude of a feature and the amount by which it alters the finger movement or force provides a metric that can be used to test the extent to which the two brain areas might be involved in that sensorimotor transformation. A strong correlation between the metric and the change in functional connectivity provides evidence that the two brain areas are performing the sensorimotor transformation.

Several of these sensory features have been identified and the project is now at the stage where metrics are being computed and the resting-state functional MR images are being analyzed for significant changes in functional connectivity. The analysis will establish the connectivity between brain areas forming the heart of the network for sensorimotor transformation. The connectivity will be compared for the three somatosensory functions to determine whether a single network performs different sensorimotor transformations or whether specific networks are required for different sensorimotor transformations.

The functional connectivity between brain areas after training on the tactile guidance task in a small sample of stroke patients will be compared to that of healthy individuals. Differences in the change in functional connectivity in the network for sensorimotor transformation will provide insight into the mechanisms responsible for impairments in sensorimotor function following stroke.

The outcome of the FIRST project will have the most direct impact on health professionals involved in rehabilitation of individuals with impaired sensorimotor function as a consequence of ischaemic or hemorrhagic brain lesions. It provides a technique for more precisely identifying the areas of the brain responsible for the impairments and for testing whether interventions have any profound effect on restoring normal functional connectivity.

In a broader context, the technique can be generalized to disorders affecting almost any brain function. This approach can be applied to any task which results in a change resting-state functional connectivity. Consequently, it can be used to diagnose which functional connections are most affected by the disorder and whether a treatment is effective restoring normal functional connectivity.

Information about the project and the most recent results can be found on the project website: