Reduction of stroke assessment time for visually guided reaching task on KINARM exoskeleton robot.

Robotic technologies provide objective, highly reliable tools for assessment of brain function following stroke. KINARM is an exoskeleton device that quantifies sensorimotor brain function using a visually guided reaching task among many other behavioral tasks. As further tasks are developed to more broadly assess different aspects of behavior using the robot, techniques and approaches are required to reduce the time it takes to complete each task. The present study investigates how the value of robot-measured parameters changes under alternative schemes that significantly reduce assessment time compared to the current assessment protocol for the visually guided reaching task. Results of the study are validated by addressing an important diagnostic question using an SVM classifier, showing that the alternative schemes provide nearly identical performance in terms of classification sensitivity, specificity and accuracy.

Distinguishing subregions of the human MT+ complex using visual fields and pursuit eye movements.

In humans, functional imaging studies have demonstrated a homologue of the macaque motion complex, MT+ [suggested to contain both middle temporal (MT) and medial superior temporal (MST)], in the ascending limb of the inferior temporal sulcus. In the macaque monkey, motion-sensitive areas MT and MST are adjacent in the superior temporal sulcus. Electrophysiological research has demonstrated that while MT receptive fields primarily encode the contralateral visual field, MST dorsal (MSTd) receptive fields extend well into the ipsilateral visual field. Additionally, macaque MST has been shown to receive extraretinal smooth-pursuit eye-movement signals, whereas MT does not. We used functional magnetic resonance imaging (fMRI) and the neural properties that had been observed in monkeys to distinguish putative human areas MT from MST. Optic flow stimuli placed in the full field, or contralateral field only, produced a large cluster of functional activation in our subjects consistent with previous reports of human area MT+. Ipsilateral optic flow stimuli limited to the peripheral retina produced activation only in an anterior subsection of the MT+ complex, likely corresponding to putative MSTd. During visual pursuit of a single target, a large portion of the MT+ complex was activated. However, during nonvisual pursuit, only the anterolateral portion of the MT+ complex was activated. This subsection of the MT+ cluster could correspond to putative MSTl (lateral). In summary, we observed three distinct subregions of the human MT+ complex that were arranged in a manner similar to that seen in the monkey.

Eye position signal modulates a human parietal pointing region during memory-guided movements.

Using functional magnetic resonance imaging, we examined the signal in parietal regions that were selectively activated during delayed pointing to flashed visual targets and determined whether this signal was dependent on the fixation position of the eyes. Delayed pointing activated a bilateral parietal area in the intraparietal sulcus (rIPS), rostral/anterior to areas activated by saccades. During right-hand pointing to centrally located targets, the left rIPS region showed a significant increase in activation when the eye position was rightward compared with leftward. As expected, activation in motor cortex showed no modulation when only eye position changed. During pointing to retinotopically identical targets, the left rIPS region again showed a significant increased signal when the eye position was rightward compared with leftward. Conversely, when pointing with the left arm, the right rIPS showed an increase in signal when eye position was leftward compared with rightward. The results suggest that the human parietal hand/arm movement region (rIPS), like monkey parietal areas (Andersen et al., 1985), exhibits an eye position modulation of its activity; modulation that may be used to transform the coordinates of the retinotopically coded target position into a motor error command appropriate for the wrist.

Recovery of fMRI activation in motion area MT following storage of the motion aftereffect.

We used functional magnetic resonance imaging (fMRI) during storage of the motion aftereffect (MAE) to examine the relationship between motion perception and neural activity in the human cortical motion complex MT+ (including area MT and adjacent motion-selective cortex). MT+ responds not only to physical motion but also to illusory motion, as in the MAE when subjects who have adapted to continuous motion report that a subsequent stationary test stimulus appears to move in the opposite direction. In the phenomenon of storage, the total decay time of the MAE is extended by inserting a dark period between adaptation and test phases. That is, when the static test pattern is presented after a storage period equal in duration to the normal MAE, the illusory motion reappears for almost as long as the original effect despite the delay. We examined fMRI activation in MT+ during and after storage. Seven subjects viewed continuous motion, followed either by an undelayed stationary test (immediate MAE) or by a completely dark storage interval preceding the test (stored MAE). Like the perceptual effect, activity in MT+ dropped during the storage interval then rebounded to reach a level much higher than after the same delay without storage. Although MT+ activity was slightly enhanced during the storage period following adaptation to continuous motion (compared with a control sequence in which the adaptation grating oscillated and no MAE was perceived), this enhancement was much less than that observed during the perceptual phenomenon. These results indicate that following adaptation, activity in MT+ is pronounced only with the presentation of an appropriate visual stimulus, during which the MAE is perceived.

H-reflex modulation during reverse passive pedalling.

During passive pedalling or walking movements of the human leg, the gain of the soleus H reflex is depressed in proportion to the rate of the movement, with the depression maximal at the end of leg flexion. In this phase, maximum flexion of the hip and knee occur at different positions. The question was raised as to whether the gain changes still occur when the direction of movement is reversed, thus reversing those positions. In four subjects, reverse passive pedalling movements of the legs were studied at two velocities, 10 and 30 rpm. Ten H reflexes per subject were elicited from popliteal fossa stimulation at eight equispaced positions around the cycle and M waves were used as an indicator of stimulation stability. For each subject, reflex attenuation occurred in the flexion phase, but unlike forward movement, peak inhibition occurred before full flexion of the knee. Movement velocity continued to determine the degree of inhibition. The reverse vs. forward difference in peak inhibition most likely reflects differences in conditioning receptor discharge from hip and knee extensor muscles, due to the differing kinematic profiles for the two movements. Therefore the spinal gain modulation appears to receive significant input from specific somatosensory discharge consequential to the movement.