Motor learning by imagery is differentially affected in Parkinson's and Huntington's diseases.

Studies of motor imagery and motor learning have thus far been concerned only with its effects on healthy subjects. Therefore, in order to investigate the possible involvement of the basal ganglia, the effectiveness of motor imagery in the acquisition of motor constants in a graphomotor trajectorial learning task was examined in 11 non-demented mildly affected Huntington's disease (HD) patients and 12 non-demented Parkinson's disease (PD) patients. The patients received, after baseline, 10 min of motor imagery training, followed by a motor practice phase. Additionally, a test battery for visual imagery abilities was administered in order to investigate possible relations between visual and motor imagery. The results showed that imagery training alone enabled the HD patients to achieve a significant approach to movement isochrony, whereas the PD patients showed no marked improvements, either with motor imagery or with motor practice. Furthermore, the PD patients had more difficulties than the HD patients in solving the visual imagery tasks. Subsequent correlational analysis revealed significant relationships between the degree of caudate atrophy in the HD patients and their performance in the visual imagery tasks. However, there were no substantial correlations between the performance on the visual imagery tasks and the improvement of motor performance through motor imagery, which indicates that visual and motor imagery are independent processes. It is suggested that the dopaminergic input to the basal ganglia plays an important role in the translation of motor representations into motor performance, whereas the caudate nucleus atrophy of the HD patients does not seem to affect motor imagery, but only the visual imagery process. Furthermore, the deficits found in PD patients might also be related to their limited attentional resources and difficulties in employing predictive motor strategies.

A mental route to motor learning: improving trajectorial kinematics through imagery training.

There are contrasting reports upon the level of effectiveness of motor imagery in learning new motor skills, but there is general consensus that motor imagery can lead to improvements in performance, especially in combination with physical practice. In the present study we examined the effectiveness of motor imagery in the acquisition of movement invariants in two grapho-motor trajectorial learning tasks with differing visuospatial components: 'Ideogram drawing' and 'connecting circles'. Two subject groups were studied: An imagery group, which underwent 10 min of motor imagery training and a control group, which practised a control visuomotor task over the same period of time. The results showed that imagery training alone enabled the subjects to achieve a significant approach to movement isochrony as well as a significant shifting of peak velocity toward the target. After a practice phase, both groups improved their performance, but the imagery group was still significantly faster than the control group. Furthermore, a series of tests measuring visual imagery abilities was administered to the subjects. There were however no significant relationships between the motor performance and the visual imagery ability levels of the subjects. It is concluded that motor imagery can improve the acquisition of the spatio-temporal patterns of grapho-motor trajectories and that there are different processes involved in visual and motor imagery.

Representations of graphomotor trajectories in the human parietal cortex: evidence for controlled processing and automatic performance.

The aim of this study was to identify the cerebral areas activated during kinematic processing of movement trajectories. We measured regional cerebral blood flow (rCBF) during learning, performance and imagery of right-hand writing in eight right-handed volunteers. Compared with viewing the writing space, increases in rCBF were observed in the left motor, premotor and frontomesial cortex, and in the right anterior cerebellum in all movement conditions, and the increases were related to mean tangential writing velocity. No rCBF increases occurred in these areas during imagery. Early learning of new ideomotor trajectories and deliberately exact writing of letters both induced rCBF increases in the cortex lining the right intraparietal sulcus. In contrast, during fast writing of overlearned trajectories and in the later phase of learning new ideograms the rCBF increased bilaterally in the posterior parietal cortex. Imagery of ideograms that had not been practised previously activated the anterior and posterior parietal areas simultaneously. Our results provide evidence suggesting that the kinematic representations of graphomotor trajectories are multiply represented in the human parietal cortex. It is concluded that different parietal subsystems may subserve attentive sensory movement control and whole-field visuospatial processing during automatic performance.

Directional hyperattention in tactile neglect within grasping space.

This study was motivated by the fact that unilateral neglect, an impediment to progress in patient rehabilitation, is often reported to occur in a wider area of space than that usually assessed in clinical settings. Neglect within "grasping space" (Halligan & Marshall, 1991; Kolb & Whishaw, 1990) was assessed via two search tasks: one in which search was guided by visual information and the other in which search was guided by tactile information. The performance of 10 left brain-damaged patients (LBD) and 20 right brain-damaged patients, 10 of whom showed left visual neglect (RBD+) while 10 did not (RBD-), was compared with that of age-matched controls. The visual search task confirmed the clinical diagnoses of unilateral visual neglect. On the tactile test, both RBD groups showed reduced search within the left hemispace, although this was a particularly strong feature of the performance of the RBD+ patients. Furthermore, this reduced leftwards exploration in RBD+ patients was associated with an increased frequency of repetitions made within the right hemispace, as had also been noted in some of these patients on conventional visual star cancellation. Results are discussed in relation to hyperattentional theories of directional spatial neglect.

Sound localization in egocentric space following hemispheric lesions.

In this paper the performance of patients with unilateral hemispheric lesions (n = 10 with right brain damage; n = 10 with left brain damage) on a free-field sound localization task was contrasted with that of healthy controls (n = 10). Sound stimuli were presented binaurally in the horizontal plane from eight loudspeakers set at azimuths between -105 degrees and +105 degrees. Whereas performance of both patient groups was generally less accurate than controls, no evidence suggested that this was specific to the contralateral hemisphere. The results indicate that both hemispheres play a role in sound localization, with systematic directional errors made towards the ipsilateral hemifield following unilateral lesions. Furthermore, particular location difficulties at pericentral positions (+15 degrees and -15 degrees) following right hemisphere damage, may indicate a specific function for the right hemisphere in determining personal frames of spatial reference within pericentral space.

Frontal and parietal transcranial magnetic stimulation (TMS) disturbs programming of saccadic eye movements.

Transcranial magnetic stimulation (TMS) of human motor cortex typically evoked motor responses. TMS has failed to elicit eye movements in humans, whereas prolongations of saccadic latency have been reported with TMS. In previous studied we demonstrated that saccades can be abolished or saccadic trajectories can be changed through TMS in the 100 msec before saccade onset. This effect was especially marked when TMS was applied parietally. TMS never influenced a saccade in flight. Simulations of predictive experimental saccades that were impaired through TMS of the frontal or parietal cortex demonstrated especially that the dynamics of small saccades were markedly influenced, resulting in a significant decrease in acceleration and amplitude, or an almost complete inhibition. The impact of inhibition through TMS was critically dependent on timing: early TMS (-70 msec) had a much larger inhibitory effect than late TMS (-20 msec) on experimental saccades. Differential timing of TMS in influencing the cortical control signal is demonstrated through simulations of a reciprocally innervated eye movement model that paralleled empirically determined changes in eye movement dynamics after real TMS. There is a reasonable match between the model and the experimental data. We conclude that the inhibitory action of a presaccadic disturbance, such as a TMS pulse, on saccadic programming is inversely related to timing and amplitude of the predicted saccade.

Associative learning in degenerative neostriatal disorders: contrasts in explicit and implicit remembering between Parkinson's and Huntington's diseases.

The performances of 12 patients with Parkinson's disease (PD), 16 with Huntington's disease (HD), and young and old healthy controls were assessed on a number of tests of verbal and nonverbal declarative memory, on a test of nonmotor conditional associative learning (words and colors), and on a number of reaction time (RT) tasks. The RT tasks consisted of cued simple and choice reactions. The relationship between the precue and the imperative stimulus in the S1-S2 paradigm was nonarbitrary in the first series and arbitrary in the second series. The series with arbitrary S1-S2 associations was repeated across two successive blocks of trials. The rationale of the study was to investigate the function of the basal ganglia "complex loop," and it was postulated that HD patients would show greater deficits because of greater involvement of the caudate nucleus. The patients with HD had the slowest RTs. Across the two blocks with arbitrary S1-S2 associations, the patients with HD but not PD nevertheless showed evidence of learning in their precued RTs. In contrast, the patients with PD were better able to remember the associations in free recall than were the HD patients. It is concluded that patients with PD have relatively greater deficits in procedural learning, whereas those with HD have relatively more impairments in declarative memory, and the greater level of cognitive impairment in HD overall is interpreted as being due to more serious damage to the caudate loop.

Successive roles of the cerebellum and premotor cortices in trajectorial learning.

The structures of the human brain engaged during learning of unilateral trajectorial hand movements were mapped by measurements of regional cerebral blood flow. Trajectorial movement velocity accelerated moderately after short-term training p < 0.025 and increased further after long-term training p < 0.01. During the early phase of learning there was a significant activation p < 0.001 of the ipsilateral dentate nucleus. By contrast, after overlearning the premotor cortical areas in both cerebral hemispheres were maximally activated p < 0.001, while the dentate nucleus was no longer activated. It is suggested that learning of new movement trajectories involves the cerebellum, while overlearned trajectorial movements engage the premotor cortex.

Conditional associative learning is impaired in cerebellar disease in humans.

Eight patients with lesions restricted to the cerebellum were compared with a total of 25 age-matched controls on a reaction time (RT) task allowing the recording of simple and choice RTs as well as RTs to abstract visual patterns signifying the particular movement to be performed. In all conditions the actual movements required (either a left or a right button press) remained the same, but the cognitive requirements of the task varied. In the abstract patterns condition, the significance of the various patterns with regard to the required movement had to be learned by the subjects. The patients with cerebellar lesions were particularly impaired in this condition. It is concluded that the cerebellum is involved not just in the timing of movements but also in the decision process as to which movement should be performed under particular circumstances.

Proximal and distal reaction times (RTs) are not differentially affected in Parkinson's disease.

The hypothesis was tested that proximal and distal reaction times (RTs) might be differentially affected in Parkinson's disease (PD). Twelve patients with PD were compared with 12 age-matched healthy controls on tests of finger-, hand-, leg-, and torso-RTs. Patients were significantly slower in initiating all movements and were slower in executing all movements except for the leg (stepping) task. Choice- versus simple-RTs were also not differentially affected in the PD group. In the healthy subjects, age was significantly positively correlated with response initiation times (RITs) but not with movement times (MTs).

Slow cortical potentials (SCPS) in schizophrenic patients during performance of the Wisconsin card-sorting test (WCST).

Fifteen schizophrenic patients (diagnosed according to DSM-III-R) and 15 age- and education-matched controls were tested on a computerized version of the Wisconsin card-sorting test (WCST). Slow Cortical Potentials (SCPs) were recorded throughout the performance from frontal, central and parietal electrode sites. As expected, the patients were impaired on the WCST, achieving fewer categories overall and incurring significantly more "unique" errors, although they were not significantly more perseverative than the controls. The patients did not display a generalized impairment in SCPs, differences between the groups emerging only before presentation of the key-cards and after presentation of the feedback regarding the correctness of the response. Neither the choice-card at the beginning of the trial, nor the presentation of the key-cards resulted in attenuated Evoked Potentials (EPs) in the patients. The lack of any abnormality in EPs suggests that the reason for the poor performances of schizophrenic patients on the WCST lies elsewhere than in perceptual stimulus processing. Contrary to expectations no specific impairment in frontal SCPs was detected.

Prism adaptation and other tasks involving spatial abilities in patients with Parkinson's disease, patients with frontal lobe lesions and patients with unilateral temporal lobectomies.

Patients in the early stages of Parkinson's disease were compared with patients who had sustained damage specific to either the frontal or temporal lobes and normal controls on a delayed alternation task, a test of the left right orientation and a prism adaptation task. On the former two tasks age accounted for more of the variability in performance than did site of brain lesion. However, patients with frontal lobe, right temporal lobe or basal ganglia damage were significantly impaired on the adaptation task. The results are discussed with regard to "switching", "sequencing" and "internal guidance" of movement hypotheses.

Classical conditioning in patients with severe memory problems.

Classical conditioning is one of the most fundamental forms of learning, and yet little is known regarding the effects of brain injury on conditioning processes in humans. Three patients with temporal lobe lesions and severe memory problems were therefore assessed in terms of eyeblink conditioning, extinction, discrimination and reversal learning, and in one patient electrodermal conditioning was also investigated. The acquisition of conditioned responses was seen to be intact, but the evidence regarding extinction was ambiguous. All of the patients were impaired in discrimination learning and also reversal learning.

Motor learning in monkeys (Macaca fascicularis) with lesions in motor thalamus.

The study examines the nature of the influence that the basal ganglia exert on frontal cortex via the motor nuclei of the thalamus. Twelve monkeys were trained to pull a handle given one colour cue and to turn it given another. Bilateral lesions were then placed in the ventral thalamus. Four monkeys with large anterior lesions including the VA nucleus and the anterior part of VLo were severely impaired at relearning the task. Monkeys with small lesions in VAmc or with lesions centred on VLo were not impaired. The analysis of the histology suggests that the impairment in the four monkeys did not result from involvement of the cerebellar relay through nucleus X. It is argued that the animals are not impaired because of faulty execution. This suggests that the basal ganglia have an influence on motor learning.

Sequence ability in parkinsonians, patients with frontal lobe lesions and patients who have undergone unilateral temporal lobectomies.

Patients in the early stages of Parkinson's disease were compared with patients who had sustained damage specific to either the frontal or temporal lobes and normal controls on a number of sequencing tests. These tests involved the reproduction of sequences of hand gestures, sequences tapped out on blocks, and sequences of digits. Only the groups with frontal lobe lesions or right temporal lobectomies were impaired on any of these tasks, though no group was impaired on all of the sequencing tasks.

The performance on learning tasks of patients in the early stages of Parkinson's disease.

It is known that in animals learning is disrupted by caudate lesions; but there has been no agreement about whether pathology in the basal ganglia causes a similar impairment in man. Nineteen patients in the early stages of Parkinson's disease were tested on two associative learning tasks and on the Wisconsin Card Sorting Task; and their performance was compared with that of patients with frontal or temporal lobe lesions. On the two associative learning tasks there was no overall difference between the Parkinsonian group and the controls. However, a minority of the Parkinsonian patients performed very poorly on these tasks; and it was noted that these tended to be the older patients.

Cognitive mapping after unilateral temporal lobectomy.

An investigation of the extension of O'KEEFE and NADEL's [The Hippocampus as a Cognitive Map. Oxford University Press, Oxford 1978] theory of hippocampal functioning is described in patients who have undergone unilateral temporal lobectomy for the relief of epilepsy. A new spatial task, incorporating a recall-for-designs test but based on studies of spatial memory and cognitive mapping in animals was devised. Results supported the prediction of temporal lobe structure involvement in the mediation of non-egocentric but not egocentric space, and of the role of right temporal lobe structures in conditions designed to encourage "place" but not "cue" learning strategies. The role of verbal mediation in task performance is also discussed.

Verbal and abstract designs paired associate learning after unilateral temporal lobectomy.

The combined use of a new abstract designs Paired Associates test with the Verbal Paired Associates test of Form 1 of the Wechsler Memory Scale was investigated with respect to eliciting material specific memory deficits after unilateral temporal lobectomy. Although the verbal test differentiated between the memory ability of these two groups more clearly than the abstract designs test, the effectiveness of looking at the difference between total scores on the two tests was demonstrated. The two tests produced similar levels of performance in control subjects.