Frontal increase of beta modulation during the practice of a motor task is enhanced by visuomotor learning

Movement is accompanied by beta power changes over frontal and sensorimotor regions: a decrease during movement (event-related desynchronization, ERD), followed by an increase (event-related synchronization, ERS) after the movement end. We previously found that enhancements of beta modulation (from ERD to ERS) during a reaching test (mov) occur over frontal and left sensorimotor regions after practice in a visuo-motor adaptation task (ROT) but not after visual learning practice. Thus, these enhancements may reflect local cumulative effects of motor learning. Here we verified whether they are triggered by the learning component inherent in ROT or simply by motor practice in a reaching task without such learning (MOT). We found that beta modulation during mov increased over frontal and left areas after three-hour practice of either ROT or MOT. However, the frontal increase was greater after ROT, while the increase over the left area was similar after the two tasks. These findings confirm that motor practice leaves local traces in beta power during a subsequent motor test. As they occur after motor tasks with and without learning, these traces likely express the cost of processes necessary for both usage and engagement of long-term potentiation mechanisms necessary for the learning required by ROT.

Electrophysiological traces of visuomotor learning and their renormalization after sleep

OBJECTIVE

Adapting movements to a visual rotation involves the activation of right posterior parietal areas. Further performance improvement requires an increase of slow wave activity in subsequent sleep in the same areas. Here we ascertained whether a post-learning trace is present in wake EEG and whether such a trace is influenced by sleep slow waves.

METHODS

In two separate sessions, we recorded high-density EEG in 17 healthy subjects before and after a visuomotor rotation task, which was performed both before and after sleep. High-density EEG was recorded also during sleep. One session aimed to suppress sleep slow waves, while the other session served as a control.

RESULTS

After learning, we found a trace in the eyes-open wake EEG as a local, parietal decrease in alpha power. After the control night, this trace returned to baseline levels, but it failed to do so after slow wave deprivation. The overnight change of the trace correlated with the dissipation of low frequency (<8 Hz) NREM sleep activity only in the control session.

CONCLUSIONS

Visuomotor learning leaves a trace in the wake EEG alpha power that appears to be renormalized by sleep slow waves.

SIGNIFICANCE

These findings link visuomotor learning to regional changes in wake EEG and sleep homeostasis.

Effects of levodopa on motor sequence learning in Parkinson's disease

BACKGROUND

Dopaminergic therapy with levodopa improves motor function in PD patients, but the effects of levodopa on cognition in PD remain uncertain.

OBJECTIVE

To use H(2)(15)O and PET to assess the effect of levodopa infusion on motor sequence learning in PD.

METHODS

Seven right-handed PD patients were scanned "on" and "off" levodopa while performing a sequence learning task. The changes in learning performance and regional brain activation that occurred during this intervention were assessed.

RESULTS

During PET imaging, levodopa infusion reduced learning performance as measured by subject report (p < 0.05). This behavioral change was accompanied by enhanced activation during treatment in the right premotor cortex and a decline in the ipsilateral occipital association area (p < 0.01). Levodopa-induced changes in learning-related activation responses in the occipital association cortex correlated with changes in learning indexes (p < 0.01).

CONCLUSIONS

Levodopa treatment appears to have subtle detrimental effects on cognitive function in nondemented PD patients. These effects may be mediated through an impairment in brain activation in occipital association cortex.

Enhancement of brain activation during trial-and-error sequence learning in early PD

BACKGROUND

Although the pathophysiology remains unknown, most nondemented patients with PD have difficulty with frontal tasks, including trial-and-error sequence learning. If given time, they can perform cognitive tasks of moderate difficulty as well as controls. However, it is not known how brain function is altered during this time period to preserve higher cortical function in the face of PD pathology.

METHOD

To evaluate this phenomenon, the authors matched sequence learning between PD and control subjects for the last 30 seconds of a PET scan. Learning during the initial 50 seconds of PET was unconstrained.

RESULTS

Learning indices were equivalent between groups during the last 30 seconds of the scan, whereas rates of acquisition, correct movements, and forgetting differed in the first 30 seconds. In normal controls sequence learning was associated with activations in the right prefrontal, premotor, parietal, rostral supplementary motor area, and precuneus regions. To achieve equal performance, the PD group activated greater volume within these same regions, and also their left sided cortical homologs and the lateral cerebellum bilaterally.

CONCLUSIONS

Mildly affected patients with PD demonstrated only modest impairment of learning during the first 30 seconds of the task and performed equivalently with controls thereafter. However, the mechanism by which they achieved equiperformance involved considerable changes in brain function. The PD group had to activate four times as much neural tissue as the controls, including recruiting brain from homologous cortical regions and bilateral lateral cerebellum.

Effects of levodopa infusion on motor activation responses in Parkinson's disease

BACKGROUND

Clinical improvement with levodopa therapy for PD is associated with specific regional changes in cerebral glucose metabolism. However, it is unknown how these effects of treatment in the resting state relate to alterations in brain function that occur during movement. In this study, the authors used PET to assess the effects of levodopa on motor activation responses and determined how these changes related to on-line recordings of movement speed and accuracy.

METHODS

Seven right-handed PD patients were scanned with H(2)15O/PET while performing a predictable paced sequence of reaching movements and while observing the same screen displays and tones. PET studies were performed during "on" and "off" states with an individually titrated constant rate levodopa infusion; movements were kinematically controlled across treatment conditions.

RESULTS

Levodopa improved "off" state UPDRS motor ratings (34%; p < 0.006) and movement time (18%; p = 0.001). Spatial errors worsened during levodopa infusion (24%; p = 0.02). Concurrent regional cerebral blood flow (rCBF) recordings revealed significant enhancement of motor activation responses in the posterior putamen bilaterally (p < 0.001), left ventral thalamus (p < 0.002), and pons (p < 0.005). Movement time improvement with treatment correlated with rCBF increases in the left globus pallidus and left ventral thalamus (p < 0.01). By contrast, the increase in spatial errors correlated with rCBF increases in the cerebellar vermis (p < 0.01).

CONCLUSION

These results suggest that levodopa infusion may improve aspects of motor performance while worsening others. Different components of the motor cortico-striato-pallido-thalamo-cortical loop and related pathways may underlie motor improvement and adverse motoric effects of levodopa therapy for PD.

Functional correlates of pallidal stimulation for Parkinson's disease

We measured regional cerebral blood flow with H2 15O and positron emission tomography (PET) scanning at rest and during a motor task to study the mechanism of motor improvement induced by deep brain stimulation of the internal globus pallidus in Parkinson's disease. Six right-handed patients with Parkinson's disease were scanned while performing a predictable paced sequence of reaching movements and while observing the same screen displays and tones. PET studies were performed ON and OFF stimulation in a medication-free state. Internal globus pallidus deep brain stimulation improved off-state United Parkinson's Disease Rating Scale motor ratings (37%, p < 0.002) and reduced timing errors (movement onset time, 55%, p < 0.01) as well as spatial errors (10%, p < 0.02). Concurrent regional cerebral blood flow recordings revealed a significant enhancement of motor activation responses in the left sensorimotor cortex (Brodmann area [BA] 4), bilaterally in the supplementary motor area (BA 6), and in the right anterior cingulate cortex (BA 24/32). Significant correlations were evident between the improvement in motor performance and the regional cerebral blood flow changes mediated by stimulation. With internal globus pallidus deep brain stimulation, improved movement initiation correlated with regional cerebral blood flow increases in the left sensorimotor cortex and ventrolateral thalamus and in the contralateral cerebellum. By contrast, improved spatial accuracy correlated with regional cerebral blood flow increases in both cerebellar hemispheres and in the left sensorimotor cortex. These results suggest that internal globus pallidus deep brain stimulation may selectively improve different aspects of motor performance. Multiple, overlapping neural pathways may be modulated by this intervention.

Functional networks in motor sequence learning: abnormal topographies in Parkinson's disease

We examined the neural circuitry underlying the explicit learning of motor sequences in normal subjects and patients with early stage Parkinson's disease (PD) using 15O-water (H2 15O) positron emission tomography (PET) and network analysis. All subjects were scanned while learning motor sequences in a task emphasizing explicit learning, and during a kinematically controlled motor execution reference task. Because different brain networks are thought to subserve target acquisition and retrieval during motor sequence learning, we used separate behavioral indices to quantify these aspects of learning during the PET experiments. In the normal cohort, network analysis of the PET data revealed a significant covariance pattern associated with acquisition performance. This topography was characterized by activations in the left dorsolateral prefrontal cortex (PFdl), rostral supplementary motor area (preSMA), anterior cingulate cortex, and in the left caudate/putamen. A second independent covariance pattern was associated with retrieval performance. This topography was characterized by bilateral activations in the premotor cortex (PMC), and in the right precuneus and posterior parietal cortex. The normal learning-related topographies failed to predict acquisition performance in PD patients and predicted retrieval performance less accurately in the controls. A separate network analysis was performed to identify discrete learning-related topographies in the PD cohort. In PD patients, acquisition performance was associated with a covariance pattern characterized by activations in the left PFdl, ventral prefrontal, and rostral premotor regions, but not in the striatum. Retrieval performance in PD patients was associated with a covariance pattern characterized by activations in the right PFdl, and bilaterally in the PMC, posterior parietal cortex, and precuneus. These results suggest that in early stage PD sequence learning networks are associated with additional cortical activation compensating for abnormalities in basal ganglia function.

Learning of visuomotor transformations for vectorial planning of reaching trajectories

The planning of visually guided reaches is accomplished by independent specification of extent and direction. We investigated whether this separation of extent and direction planning for well practiced movements could be explained by differences in the adaptation to extent and directional errors during motor learning. We compared the time course and generalization of adaptation with two types of screen cursor transformation that altered the relationship between hand space and screen space. The first was a gain change that induced extent errors and required subjects to learn a new scaling factor. The second was a screen cursor rotation that induced directional errors and required subjects to learn new reference axes. Subjects learned a new scaling factor at the same rate when training with one or multiple target distances, whereas learning new reference axes took longer and was less complete when training with multiple compared with one target direction. After training to a single target, subjects were able to transfer learning of a new scaling factor to previously unvisited distances and directions. In contrast, generalization of rotation adaptation was incomplete; there was transfer across distances and arm configurations but not across directions. Learning a rotated reference frame only occurred after multiple target directions were sampled during training. These results suggest the separate processing of extent and directional errors by the brain and support the idea that reaching movements are planned as a hand-centered vector whose extent and direction are established via learning a scaling factor and reference axes.

Visual feedback has differential effects on reaching movements in Parkinson's and Alzheimer's disease

We examine the role of visual feedback in the programming and execution of reaching movement in patients with Parkinson's disease without cognitive impairment and patients with Alzheimer's disease without extrapyramidal signs. Controls were normally aging subjects. All subjects moved a cursor to targets on a digitizing tablet without seeing their limb. Starting and target positions were always visible on a screen while, during movement, cursor position was either visible or blanked. They were instructed to make uncorrected movements, as fast and as accurate as possible without minimizing reaction time. In absence of visual feedback, movement accuracy in patients with AD was severely impaired. Hand paths of parkinsonian patients were as accurate as normal subjects' with similar temporal velocity profiles and movement speed. With cursor feedback, accuracy was the same in the three groups, although movement speed and transport phase in patients with Alzheimer's disease were significantly reduced compared to the other groups. Also, movements of parkinsonian patients showed shorter transport phase and lower mean velocity than controls'. The different characteristics of the motor performance suggests that in the two diseases visual information is used differently for both motor programming and execution: patients with Alzheimer's disease, while scarcely using feed forward commands, relied on continuous on-line external cues. The correlation of motor performance with cognitive impairment argues against the hypothesis of basal ganglia involvement in AD. The motor abnormalities we found may represent early subclinical manifestation of apraxic disturbance. Parkinsonian patients showed higher reliance on feedback commands only with cursor feedback: this could be explained by their difficulty in engaging effectively automatic routines when distractors are present.

Independent learning of internal models for kinematic and dynamic control of reaching

Psychophysical studies of reaching movements suggest that hand kinematics are learned from errors in extent and direction in an extrinsic coordinate system, whereas dynamics are learned from proprioceptive errors in an intrinsic coordinate system. We examined consolidation and interference to determine if these two forms of learning were independent. Learning and consolidation of two novel transformations, a rotated spatial reference frame and altered intersegmental dynamics, did not interfere with each other and consolidated in parallel. Thus separate kinematic and dynamic models were constructed simultaneously based on errors computed in different coordinate frames, and possibly, in different sensory modalities, using separate working-memory systems. These results suggest that computational approaches to motor learning should include two separate performance errors rather than one.

Impaired movement control in Alzheimer's disease

Movement accuracy in normal subjects depends on feedforward commands based on representation in memory of spatial and biomechanical features. Here we ask whether memory deficits in Alzheimer's disease (AD) interfere with movement planning and execution. Nine AD patients and nine age-matched controls moved a cursor to targets without seeing their limb. Starting and target positions were always visible on a screen, while, during movement, cursor position was either visible or blanked. Patients' paths showed discontinuous segments and prolonged movement time; movement inaccuracy, which increased without visual feedback, correlated significantly with scores of disease severity, working memory and attention.

Discrete and continuous planning of hand movements and isometric force trajectories

We have previously demonstrated that, in preparing themselves to aim voluntary impulses of isometric elbow force to unpredictable targets, subjects selected default values for amplitude and direction according the range of targets that they expected. Once a specific target appeared, subjects specified amplitude and direction through parallel processes. Amplitude was specified continuously from an average or central default; direction was specified stochastically from one of the target directions. Using the same timed response paradigm, we now report three experiments to examine how the time available for processing target information influences trajectory characteristics in two-degree-of-freedom forces and multijoint movements. We first sought to determine whether the specification of force direction could also take the form of a discrete stochastic process in pulses of wrist muscle force, where direction can vary continuously. With four equiprobable targets (two force amplitudes in each of two directions separated by 22 degrees or 90 degrees), amplitude was specified from a central default value for both narrow and wide target separations as a continuous variable. Direction, however, remained specified as a discrete variable for wide target separations. For narrow target separations, the directional distribution of default responses suggested the presence of both discrete and central values. We next examined point-to-point movements in a multijoint planar hand movement task with targets at two distances and two directions but at five directional separations (from 30 degrees to 150 degrees separation). We found that extent was again specified continuously from a central default. Direction was specified discretely from alternative default directions when target separation was wide and continuously from a central default when separation was narrow. The specification of both extent and direction evolved over a 200-ms time period beginning about 100 ms after target presentation. As in elbow force pulses, extent was specified progressively in both correct and wrong direction responses through a progressive improvement in the scaling of acceleration and velocity peaks to the target. On the other hand, movement time and hand path straightness did not change significantly in the course of specification. Thus, the specification of movement time and linearity, global features of the trajectories, are given priority over the specific values of extent and direction. In a third experiment, we varied the distances between unidirectional target pairs and found that movement extent is specified discretely, like direction, when the disparity in distances is large. The implications of these findings for contextual effects on trajectory planning are discussed. The independence of extent and direction specification and the prior setting of response duration and straightness provide critical support for the hypothesis that point-to-point movements are planned vectorially.

Learning a visuomotor transformation in a local area of work space produces directional biases in other areas

1. The dependence of directional biases in reaching movements on the initial position of the hand was studied in normal human subjects moving their unseen hand on a horizontal digitizing tablet to visual targets displayed on a vertical computer screen. 2. When initial hand positions were to the right of midline, movements were systematically biased clockwise. Biases were counterclockwise for starting points to the left. Biases were unaffected by the screen location of the starting and target positions. 3. Vision of the hand in relation to the target before movement, as well as practice with vision of the cursor during the movement, temporarily eliminated these biases. The spatial organization of the biases suggests that, without vision of the limb, the nervous system underestimates the distance of the hand from an axis or plane that includes its most common operating location. 4. To test the hypothesis that such an underestimate might represent an adaptation to a local area of work space or range effect, subjects were trained to reach accurately from right or left positions. After training, movements initiated from other locations, including ones that were previously error free, showed new biases that again represented underestimates of the distance of the initial hand position from the new trained location. 5. We conclude that hand path planning is dependent on learned representations of the location of the hand in the work space.

Control of limb dynamics in normal subjects and patients without proprioception

1. We recently showed that patients lacking proprioceptive input from their limbs have particular difficulty performing multijoint movements. In a pantomimed slicing gesture requiring sharp reversals in hand path direction, patients showed large hand path distortions at movement reversals because of failure to coordinate the timing of the separate reversals at the shoulder and elbow joints. We hypothesized that these reversal errors resulted from uncompensated effects of inertial interactions produced by changes in shoulder joint acceleration that were transferred to the elbow. We now test this hypothesis and examine the role of proprioceptive input by comparing the motor performance of five normal subjects with that of two patients with large-fiber sensory neuropathy. 2. Subjects were to trace each of six template lines presented randomly on a computer screen by straight overlapping out-and-back movements of the hand on a digitizing tablet. The lines originated from a common starting position but were in different directions and had different lengths. Directions and lengths were adjusted so that tracing movements would all require the same elbow excursion, whereas shoulder excursion would vary. The effects of varying interaction torques on elbow kinematics were then studied. The subject's dominant arm was supported in the horizontal plane by a low-inertia brace equipped with ball bearing joints and potentiometers under the elbow and shoulder. Hand position was monitored by a magnetic pen attached to the brace 1 cm above a digitizing tablet and could be displayed as a screen cursor. Vision of the subject's arm was blocked and the screen cursor was blanked at movement onset to prevent visual feedback during movement. Elbow joint torques were calculated from joint angle recordings and compared with electromyographic recordings of elbow joint musculature. 3. In control subjects, outward and inward paths were straight and overlapped the template lines regardless of their direction. As prescribed by the task, elbow kinematics remained the same across movement directions, whereas interaction torques varied substantially. The timing of the onsets of biceps activity and the offsets of triceps activity during elbow flexion varied systematically with direction-dependent changes in interaction torques. Controls exploited or dampened these interaction torques as needed to meet the kinematic demands of the task. 4. In contrast, the patients made characteristic errors at movement reversals that increased systematically across movement directions. These reversal errors resulted from improper timing of elbow and shoulder joint reversals.(ABSTRACT TRUNCATED AT 400 WORDS)

Impairments of reaching movements in patients without proprioception. I. Spatial errors

1. This paper introduces a series of studies in which we analyze the impairments in a planar reaching task in human patients with severe proprioceptive deficits resulting from large-fiber sensory neuropathy. We studied three patients, all of whom showed absence of discriminative tactile sensation, position sense, and stretch reflexes in the upper extremities. Muscle strength was normal. We compared the reaching movements of the patients with those of normal control subjects. The purpose of this first paper was no characterize the spatial errors in these patients that result primarily from impairments in the planning and execution of movement rather than in feedback control. This was done by using a task in which visual feedback of errors during movement was prevented. 2. Subjects were instructed to move their hand from given starting positions of different targets on a horizontal digitizing tablet. Hand position and targets were displayed on a computer screen. Subjects could not see their hand, and the screen display of hand position was blanked at the signal to move. Thus visual feedback during movement could not be used to achieve accuracy. Movement paths were displayed as knowledge of results after each trial. 3. Compared with controls, the patients made large spatial errors in both movement direction and extent. Directional errors were evident from movement onset, suggesting that they resulted from improper planning. In addition, patients' hand paths showed large curves and secondary movements after initial stops. 4. The overall control strategy used by patients appeared the same as that used by controls. Hand trajectories were approximately bell shaped, and movement extent was controlled by scaling a trajectory waveform in amplitude and time. However, both control subjects and patients showed systematic errors in movement extent that depended on the direction of hand movement. In control subjects, these systematic dependencies of extent on direction were small, but in patients they produced large and prominent errors. Analysis of the hand trajectories revealed that errors were associated with differences in velocity and acceleration for movements in different directions. In an earlier study, we showed that in subjects with normal sensation that the dependence of acceleration and velocity on direction results from a failure to take the inertial properties of the limb into account in programming the initial trajectory. In control subjects, these differences in initial acceleration are partially compensated by direction-dependent variations in movement time.(ABSTRACT TRUNCATED AT 400 WORDS)

Impairments of reaching movements in patients without proprioception. II. Effects of visual information on accuracy

1. The aim of this study was to determine how vision of a cursor indicating hand position on a computer screen or vision of the limb itself improves the accuracy of reaching movements in patients deprived of limb proprioception due to large-fiber sensory neuropathy. In particular, we wished to ascertain the contribution of such information to improved planning rather than to feedback corrections. We analyzed spatial errors and hand trajectories of reaching movements made by subjects moving a hand-held cursor on a digitizing tablet while viewing targets displayed on a computer screen. The errors made when movements were performed without vision of their arm or of a screen cursor were compared with errors made when this information was available concurrently or prior to movement. 2. Both monitoring the screen cursor and seeing their limb in peripheral vision during movement improved the accuracy of the patients' movements. Improvements produced by seeing the cursor during movement are attributable simply to feedback corrections. However, because the target was not present in the actual workspace, improvements associated with vision of the limb must involve more complex corrective mechanisms. 3. Significant improvements in performance also occurred in trials without vision that were performed after viewing the limb at rest or during movements. In particular, prior vision of the limb in motion improved the ability of patients to vary the duration of movements in different directions so as to compensate for the inertial anisotropy of the limb. In addition, there were significant reductions in directional errors, path curvature, and late secondary movements. Comparable improvements in extent, direction, and curvature were produced when subjects could see the screen cursor during alternate movements to targets in different directions. 4. The effects of viewing the limb were transient and decayed during a period of minutes once vision of the limb was no longer available. 5. It is proposed that the improvements in performance produced after vision of the limb were mediated by the visual updating of internal models of the limb. Vision of the limb at rest may provide configuration information while vision of the limb in motion provides additional dynamic information. Vision of the cursor and the resulting ability to correct ongoing movements, however, is considered primarily to provide information about the dynamic properties of the limb and its response to neural commands.

Accuracy of planar reaching movements. II. Systematic extent errors resulting from inertial anisotropy

This study examines the source of direction-dependent errors in movement extent made by human subjects in a reaching task. As in the preceding study, subjects were to move a cursor on a digitizing tablet to targets displayed on a computer monitor. Movements were made without concurrent visual feedback of cursor position, but movement paths were displayed on the monitor after the completion of each movement. We first examined horizontal hand movements made at waist level with the upper arm in a vertical orientation. Targets were located at five distances and two directions (30 degrees and 150 degrees) from one of two initial positions. Trajectory shapes were stereotyped, and movements to more distant targets had larger accelerations and velocities. Comparison of movements in the two directions showed that in the 30 degrees direction responses were hypermetric, accelerations and velocities were larger, and movement times were shorter. Since movements in the 30 degrees direction required less motion of the upper arm than movements in the 150 degrees direction, we hypothesized that the differences in accuracy and acceleration reflected a failure to take into account the difference in total limb inertia in the two directions. To test this hypothesis we simulated the initial accelerations of a two-segment limb moving in the horizontal plane with the hand at shoulder level when a constant force was applied at the hand in each of 24 directions. We compared these simulated accelerations to ones produced by our subjects with their arms in the same position when they aimed movements to targets in the 24 directions and at equal distances from an initial position. The magnitudes of both simulated and actual accelerations were greatest in the two directions perpendicular to the forearm, where inertial resistance is least, and lowest for movements directed along the axis of the forearm. In all subjects, the directional variation in peak acceleration was similar to that predicted by the model and shifted in the same way when the initial position of the hand was displaced. The pattern of direction-dependent variations in initial acceleration did not depend on the speed of movement. It was also unchanged when subjects aimed their movements toward targets presented within the workspace on the tablet instead of on the computer monitor. These findings indicate that, in programming the magnitude of the initial force that will accelerate the hand, subjects do not fully compensate for direction dependent differences in inertial resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Accuracy of planar reaching movements. I. Independence of direction and extent variability

This study examined the variability in movement end points in a task in which human subjects reached to targets in different locations on a horizontal surface. The primary purpose was to determine whether patterns in the variable errors would reveal the nature and origin of the coordinate system in which the movements were planned. Six subjects moved a hand-held cursor on a digitizing tablet. Target and cursor positions were displayed on a computer screen, and vision of the hand and arm was blocked. The screen cursor was blanked during movement to prevent visual corrections. The paths of the movements were straight and thus directions were largely specified at the onset of movement. The velocity profiles were bell-shaped, and peak velocities and accelerations were scaled to target distance, implying that movement extent was also programmed in advance of the movement. The spatial distributions of movement end points were elliptical in shape. The major axes of these ellipses were systematically oriented in the direction of hand movement with respect to its initial position. This was true for both fast and slow movements, as well as for pointing movements involving rotations of the wrist joint. Using principal components analysis to compute the axes of these ellipses, we found that the eccentricity of the elliptical dispersions was uniformly greater for small than for large movements: variability along the axis of movement, representing extent variability, increased markedly but nonlinearly with distance. Variability perpendicular to the direction of movement, which results from directional errors, was generally smaller than extent variability, but it increased in proportion to the extent of the movement. Therefore, directional variability, in angular terms, was constant and independent of distance. Because the patterns of variability were similar for both slow and fast movements, as well as for movements involving different joints, we conclude that they result largely from errors in the planning process. We also argue that they cannot be simply explained as consequences of the inertial properties of the limb. Rather they provide evidence for an organizing mechanism that moves the limb along a straight path. We further conclude that reaching movements are planned in a hand-centered coordinate system, with direction and extent of hand movement as the planned parameters. Since the factors which influence directional variability are independent of those that influence extent errors, we propose that these two variables can be separately specified by the brain.

The effect of levo-acetyl-carnitine on visual cognitive evoked potentials in the behaving monkey

We studied acute and chronic effects of levo-acetyl-carnitine (LAC) on event-related potentials (ERPs) in 3 monkeys trained in a "go"/"no-go" visual "oddball" discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing in their respective orientation only (0 degrees or 45 degrees). Each monkey was trained to release a lever during a prespecified time window. Target stimulus presentation probabilities were between 0.25 and 0.5. ERPs had comparable mean latencies and amplitudes in all monkeys. Primary evoked potentials recorded to either the target or non-target stimulus did not change significantly as a result of LAC treatment. On the other hand, P300 latency decreased following LAC administration, with a maximum occurring in 15-20 min. The major effects of LAC were consistent within each animal and for all three of them.

Acetyl-levo-carnitine protects against MPTP-induced parkinsonism in primates

Acetyl-levo-carnitine (ALC) protects against 1-methyl, 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity in the nonhuman primate. ALC pretreated monkeys do not show signs of parkinsonism or electroretinographic changes typical of dopaminergic deficiency when given MPTP. In addition, pilot neurochemical and morphological data confirm a partial protection effect. While MAO-B inhibitors, like L-Deprenyl, are thought to protect dopaminergic neurons from MPTP-induced cell death by preventing the conversion of MPTP to its toxic metabolite MPP+, ALC is not known to have MAO-B affinity. Converging evidence suggests that ALC may affect directly mitochondrial respiration, which is known to be the target of MPP+ and affected in human neurodegenerative diseases, including Parkinson's disease. The results of this study point to new therapeutic avenues for the treatment of these nosologic entities.

Visual 'cognitive' evoked potentials in the behaving monkey

Using a visual 'oddball' paradigm we studied ERPs in monkeys trained in a 'go' 'no-go' discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing only in orientation (0 degrees or 25 degrees). Monkeys released a lever during 1 of 2 response windows (RW), 480-1762 or 740-1672 msec, following target stimulus onset. Target stimulus presentation probabilities were 1.0, 0.5 and 0.3. The primary evoked potentials recorded to either the target or non-target stimulus were similar in all monkeys. P3 signals progressively emerged in the monkeys only to the target stimulus. P3 recorded at Cz, P3, and P4 had similar mean latencies and amplitudes. Eye movements showed no relationship to P3 potentials. Neither the primary visual potentials nor P3 changed significantly as a function of RW. P3 amplitude was inversely related to target probability. When the target stimulus was presented 100% of the time (P = 1.0) P3 disappeared over 4-5 blocks of trials, while the primary evoked potentials remained consistent.

N70 and P100 can be independently affected in multiple sclerosis

We have studied the relationship between N70 and P100 of the pattern visual evoked potential in 98 patients with multiple sclerosis and in 59 controls. In patients with multiple sclerosis, P100 was either absent or had prolonged latency in 121 eyes (61.7%), while N70 was absent or prolonged in 97 eyes (49.5%). The total number of eyes with either N70 and/or P100 abnormalities was 137 (69.9%). Eighty eyes (40.8%) had abnormal latency of both P100 and N70, while 41 eyes showed P100 delays without corresponding N70 changes. Seventeen eyes had abnormal N70, but normal P100 latency. N70 and P100 appear to be more often absent in the definite rather than in the possible multiple sclerosis group. These data show that N70 and P100 can be independently affected in patients with MS.

Attenuation of the early anterior negativity of median nerve somatosensory evoked potential in the MPTP-treated monkey

Median nerve somatosensory evoked potentials (SEP) were recorded in 7 Cynomolgus monkeys, before and after the administration of N-Methyl 1,4 Phenyl 1,2,3,6 tetrahydropiridine (MPTP), a neurotoxin which induces a parkinsonian syndrome in primates. Following MPTP administration, the amplitude of the negative component recorded at 15 ms over the frontal derivations (N15) decreased by 70% or more. This amplitude reduction was not modified by administration of dopamine precursors. These findings shed light on recent findings in human parkinsonian patients.

Mapping of event-related potentials to auditory and visual odd-ball paradigms

This paper reports the results of recordings and maps of event-related potentials (ERPs) obtained in normal subjects, patients with Alzheimer's disease (AD), progressive supranuclear palsy, confusional states, and in subjects with homonymous hemianopsia. ERPs were recorded from 19 scalp electrode derivations using both visual and acoustic paradigms. In normal subjects, the topographical distribution of all ERP components is described in detail. In 45% of AD patients, ERPs were normal; in 35%, although present, ERP components were delayed, while in the other 20% the N2 and P3 peaks could not be recorded. In patients with progressive supranuclear palsy, the normal ERP sequence was not identified. Our findings in normals and in hemianopic patients suggest that the early modulation of stimulus-related potentials could be located in primary associative areas, and that N2, P3a, P3b, SW should have different origins.

The effect of intraocular 6-hydroxydopamine on retinal processing of primates

In previous studies, we showed that in the monkey, systemically administered N-methyl, 4-phenyl, 1-2-3-6 tetrahydropyridine (MPTP) produces a chronic parkinsonian syndrome accompanied by spatial frequency-dependent abnormalities in both the pattern electroretinogram and visual evoked potential. We describe the effect of intravitreally administered 6-hydroxydopamine (6-OH-DA) on the pattern electroretinogram and pattern visual evoked potential of 3 aphakic monkeys. Because of the aphake condition, several complexities of intravitreal injection of 6-OH-DA could be avoided. Nevertheless, following 6-OH-DA treatment, both the phase and the amplitude of pattern electroretinogram and pattern visual evoked potential became abnormal. This abnormality was most pronounced for the higher spatial frequencies (2.5 and 3.5 cycles per degree), whereas lower spatial frequencies (0.5 and 1.2 cycles per degree) were less impaired. The effects of systemically administered MPTP on pattern electroretinogram and pattern visual evoked potential are similar to the effects of intravitreal injections of 6-OH-DA, suggesting that a retinal catecholaminergic system plays an important role in pattern vision of primates.

Alterations in event-related potentials (ERPs) of MPTP-treated monkeys

Using an auditory 'oddball' paradigm and classical conditioning, we have studied auditory evoked potentials (AEPs) and P300-like potentials in monkeys pre- and post-MPTP treatment. Free-field acoustic stimuli were 500 Hz and 4000 Hz tones, which were designated as the 'frequent' and 'rare' conditions, respectively. The 4000 Hz stimuli were reinforced with mild somatosensory electrical stimulation. During the first few weeks following 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) administration, all monkeys gradually developed a parkinsonian syndrome, which partially, but not completely improved within 30-40 days in 2 animals. The amplitudes of the AEP were initially significantly decreased, but progressively returned to pretreatment magnitudes in the 2 monkeys which partially recovered. P300-like potentials were initially abolished in all animals; however, 30-40 days later P300 spontaneously re-emerged in the same 2 monkeys. Latencies of both of these signals were unaffected by MPTP. Acute administration of dopamine precursor during the first phase of neurotoxicity partially and temporarily improved depressed AEP amplitudes, but did not restore absent P300-like potentials. The relevance of these results for Parkinson's disease is discussed.

Spatial frequency-dependent abnormalities of the pattern electroretinogram and visual evoked potentials in a parkinsonian monkey model

The pattern visual evoked potential (PVEP) and pattern electroretinogram (PERG) were studied in 5 cynomolgus monkeys before and during the development of a parkinsonian syndrome induced by MPTP. The stimuli were vertical bars of four spatial frequencies (0.5, 1.2, 2.5 and 3.5 cycles/degree (cpd) modulated at temporal rates of 1, 4, 6, and 8 Hz. Following MPTP administration, all monkeys developed parkinsonian signs accompanied by changes in the amplitude and latency of the PVEP and PERG. Sinemet L-dopat carbi olopa administration produced temporary recovery of both PVEP and PERG. Two of the monkeys were followed for a prolonged period: 30-40 days after MPTP, the parkinsonian signs showed partial recovery; the PVEP latency and amplitude to 2.5 and 3.5 cpd stimuli and the latency to 1.2 cpd showed improvement but remained abnormal. The latencies of PERGs were normal, but the amplitudes were significantly reduced when stimuli of 2.5 and 3.5 cpd were used. Both PVEP and PERG to 0.5 cpd stimuli returned to normal. No further modifications were seen in the recordings performed 6 months and 1 year later. This study demonstrates (1) that spatial frequency-dependent electrophysiological abnormalities occur in the MPTP-treated monkey, a result previously found in human Parkinson's disease, and (2) that dopamine has a specific function in neurotransmission in the visual system of primates.

Systemic 1-methyl,4-phenyl,1-2-3-6-tetrahydropyridine (MPTP) administration decreases retinal dopamine content in primates

Following MPTP administration, 4 Cynomolgus monkeys developed a parkinsonian syndrome, accompanied by specific changes of both pattern visual evoked potential and electroretinogram. Retinal dopamine and dihydroxyphenylacetic acid contents were measured in the 4 MPTP-treated monkeys and in 3 normal monkeys. Dopamine and dihydroxyphenylacetic acid levels were significantly lower in the retinas of the MPTP-treated animals (p less than 0.001), suggesting that dopamine has a specific function in the visual system of primates.

Scalp distribution of pattern visual evoked potentials in normal and hemianopic monkeys

We examined the hemispheric distribution of the pattern visual evoked potential in 3 Cynomolgus monkeys, before and after right optic tractotomy or left occipital lobectomy. The stimuli were vertical gratings of 4 spatial frequencies, presented using counterphase and on-off modulation at 1 and 8 Hz. In the normal monkey, the amplitude and latency of the PVEPs elicited by 1 Hz stimulation were similar across all electrode sites. While no differences were found in the phase of the PVEP elicited by 8 Hz stimulation across the different derivations, PVEP amplitude generally decreased over the lateral electrodes. Once experimental hemianopia was created, PVEPs recorded over the midline and the intact hemisphere were normal. However, partially polarity-inverted PVEPs of smaller amplitude were recorded over the deafferented hemisphere. In addition, the interhemispheric phase difference became more prominent in the PVEP recorded over the deafferented hemisphere as the spatial frequency was increased.

Reproducibility of cardiovascular autonomic tests in diabetics with and without autonomic dysfunction and in normal controls

The present study evaluates the reproducibility of five cardiovascular reflex tests, deep breathing (DB), Valsalva maneuver (VM), sustained hand-grip (SHG), postural hypotension (PH) and lying to standing (LS) in normal subjects and in insulin dependent (type I) diabetic patients. The study was carried out in 10 normal subjects, in 10 diabetics with autonomic neuropathy and in 10 diabetics without autonomic neuropathy. The five cardiovascular reflex tests were performed five times on five consecutive days by the same investigator and in identical basal conditions. The intraindividual variability of DB, LS and VM was significantly reduced in diabetics with autonomic neuropathy compared with normal controls, but there was no difference between diabetics without neuropathy and normal controls. The intraindividual variability of PH was significantly increased in diabetics with autonomic neuropathy compared with diabetics without autonomic neuropathy and with normal controls. There was no difference among the three groups in the reproducibility of SHG. In normal subjects the intraindividual variability only exceptionally produced a shift from normal to abnormal values or vice versa; in diabetics with autonomic neuropathy this shift was more frequent.

Visual evoked potentials in parkinsonism and dopamine blockade reveal a stimulus-dependent dopamine function in humans

VEPs were recorded with three different spatial frequencies of stimulation in patients affected by idiopathic Parkinsonism and by Parkinsonian syndromes. The detection of VEP abnormalities in Parkinson's disease was dependent on the spatial frequency of the visual stimulus (a vertical square wave grating). The VEP latency was normal in Parkinsonian syndrome patients (except in one patient affected by familial Parkinsonism). Dopamine precursor therapy differently reduced the VEP latency, depending on the spatial frequency of the visual stimulus. These findings suggest that the dopaminergic mechanism involved in the generation of VEP delays is sensitive to stimulus spatial frequency. The study of VEPs before and after the administration of haloperidol confirmed this hypothesis. VEP latency did not correlate with the major clinical symptoms of Parkinson's disease and could not predict the results of chronic dopaminergic therapy.

P300-like potentials in the normal monkey using classical conditioning and an auditory 'oddball' paradigm

Endogenous components of evoked potentials resembling P300 in humans were sequentially studied in 3 cynomolgus monkeys (Macaca fascicularis) using an auditory 'oddball' paradigm. The two different auditory stimuli were 500 Hz and 4000 Hz tones, designated as the 'frequent' and 'rare' stimuli, respectively. The probability of 'rare' tone presentation was initially 0.2. We further used probabilities of 0.1, 0.3 and 0.5. The 'rare' stimulus was reinforced by electrical stimulation, which followed the onset of the high tone by 700 msec. After 3-5 training sessions, a late positive wave was observed following the 'rare' tone. The latency of this P300-like signal was 314 +/- 16.2 msec, and the amplitude was 23.6 +/- 3.14 microV. The amplitude of this potential was modified by changes in stimulus presentation probability and by withholding reinforcement.

Presence of carpal tunnel syndrome in diabetics: effect of age, sex, diabetes duration and polyneuropathy

Common thought is that diabetic neuropathy is a predisposing factor to entrapment syndromes. Carpal tunnel syndrome (CTS) is the most frequent entrapment neuropathy; females and old people are most frequently affected (Comi et al., 1978). Prevalence of CTS in diabetics and associated risk factors were studied in 401 patients (208 males and 193 females) with insulin-dependent and non-insulin-dependent diabetes using electrophysiological techniques. Median nerve sensory and motor conduction velocity, ulnar and peroneal nerve motor conduction velocity and sural nerve sensory conduction velocity were investigated in all patients. Diagnostic criteria for CTS were the presence of delayed median nerve sensory conduction velocity in the palm-wrist tract and of increased distal motor latency. Polyneuropathy was defined by slowing-down of conduction velocity in two or more nerves. Forty-five patients (11.2%), 36 females and 9 males, showed CTS. One-hundred-sixty-eight patients (41.8%), 74 females and 94 males, were suffering from peripheral neuropathy. The strongest risk factors for CTS, in order of importance, were: female sex, older age and presence of neuropathy. Polyneuropathy but not CTS was related to duration of diabetes.