Eye tracking during a visual paired comparison task as a predictor of early dementia.

The authors present findings from a behavioral task (visual paired comparison) using infrared eye-tracking that could potentially be useful in predicting the onset of Alzheimer's disease. Delay intervals of 2 seconds and 2 minutes were used between the initial viewing of a picture and when the picture was displayed alongside a novel picture. Eye-tracking revealed that at the 2-second delay, 6 patients with mild cognitive impairment, 15 matched control participants (normal control), and 4 neurological control participants with Parkinson's disease performed comparably, viewing the novel picture greater than 71% of the time. When the delay increased to 2 minutes, patients with mild cognitive impairment viewed the novel picture only 53% of the time (P < .05), while control participants and participants with Parkinson's disease remained above 70%. These findings demonstrate the usefulness of this task for assessing normal as well as impaired memory function.

Motor subcircuits mediating the control of movement extent and speed.

The functional correlates of movement extent, speed, and covariates were investigated using PET mapping of regional cerebral blood flow (rCBF) in 13 healthy right-handed adults. A whole-arm smooth pursuit tracking task was used to strictly control potential confounds such as movement duration, error, and feedback control. During each of four scans, images of relative rCBF were obtained while subjects matched the constant velocity movements of a target using a joystick-controlled cursor. Between scans, subjects were completely adapted to one of four joystick-to-cursor gains, thereby allowing constant visual stimulation and eye movements across arm movements that ranged in extent from 6 to 24 cm. Subjects were unaware of the changes in visuomotor gain. Analyses of arm and eye movements indicated that the only significant difference in behavior across the four gain conditions was the extent and velocity of arm movements, which were closely correlated with each other. Parametric statistical methods identified brain areas where rCBF covaried with the mean movement extent of individual subjects during individual scans. Increasing movement extent was associated with parallel increases of rCBF in bilateral basal ganglia (BG; putamen and globus pallidus) and ipsilateral cerebellum. Modest extent effects were detected also in the sensorimotor cortices bilaterally. No significant inverse relations were found. We conclude that a small subcircuit within the motor control system contributes to the control of movement extent and covariates and that the BG and cerebellum play central roles in the operation of that circuit.

Neural activity in monkey dorsal and ventral cingulate motor areas: comparison with the supplementary motor area.

The cingulate motor areas are a recently discovered group of discrete cortical regions located in the cingulate sulcus with direct connections to the primary motor cortex and spinal cord. Although much is known about their anatomical relationship with other motor areas, relatively little is known about their functional neurophysiology. We investigated neural mechanisms of motor processing in the dorsal and ventral cingulate motor areas (CMAd and CMAv) during two-dimensional visually guided arm movements. Single-neuron activity in CMAd and CMAv was recorded during an instructed delay task requiring combined elbow and shoulder movements. Neural activity associated with the onset of a visual cue (signal activity), delay (set activity), and motor response (movement activity) were assessed, and their onset time, duration, magnitude, and parameters of directional specificity were calculated. To determine how CMAd and CMAv compared with other premotor areas, we also analyzed the activity of neurons in the supplementary motor area (SMA) during the same task in the same monkeys. Comparison of CMAd, CMAv, and SMA revealed remarkably similar response properties. All three areas contained signal, set, and movement activity in similar proportions and in all possible combinations within single neurons. The average onset time of signal and set activity and the duration of signal activity were not significantly different across areas. The directional tuning of activities in all three areas were uniformly distributed and highly correlated within the same neuron. There were, however, some notable differences in movement activity between motor areas. Neurons with only movement activity were more numerous in CMAd and CMAv, whereas neurons with both set and movement activity were more prevalent in SMA. Furthermore, movement activity in SMA began earlier and had a shorter duration than movement activity in CMAd and CMAv, although there was substantial overlap in their distributions. These results indicate that CMAd and CMAv participate in the visual guidance of limb movements using similar neurophysiological mechanisms as SMA. The earlier average onset and shorter duration of movement activity in SMA suggest a more prominent role for this area in movement initiation, whereas the later onset and longer duration of movement activity in CMAd and CMAv suggest a more influential role in movement execution. Notwithstanding these differences, however, the remarkable similarities in response types and their combinatorial organization within single neurons across all cortical areas attests to the parallel organization and distributed nature of information processing in these three motor areas.