The shadow of movement

Summary Movement is preceded, accompanied and followed by reactions which give to the primary action its correct execution and ensure that the body's axis, together with the limbs, maintains the right balance. If these reactions are interfered with, incoordination of movement, lack of balance, hypertonia or dystonia may all appear. In the case of dystonia, postural mechanisms tend to become dominant and take over from the kinetic component of movement. In the upper limbs, the dystonic posture follows patterns analogous to those used by monkeys for postural purposes. Thus, while the initial mechanisms of movement represent highly sophisticated processes thoroughly adapted to living in an upright state, the reactions that go with the movement are more primitive and probably have a less helpful role.The Presidential Address to the 2nd European Neurological Society Meeting, Brighton, 1990     

Lesions to the subthalamic nucleus decrease impulsive choice but impair autoshaping in rats: the importance of the basal ganglia in Pavlovian conditioning and impulse control

Although the subthalamic nucleus (STN) is involved in regulating motor function, and inactivation of this structure relieves the motor symptoms in Parkinsonian patients, recent data indicate that corticosubthalamic connections are involved in both the regulation of attention and the ability to withhold from responding. Considerable evidence suggests that the neural circuitry underlying such behavioural disinhibition or impulsive action can be at least partially dissociated from that implicated in impulsive decision-making and it has been suggested that the tendency to choose impulsively is related to the ability to form and use Pavlovian associations. To explore these hypotheses further, STN-lesioned rats were tested on the delay-discounting model of impulsive choice, where impulsivity is defined as the selection of a small immediate over a larger delayed reward, as well as in a rodent autoshaping paradigm. In contrast to previous reports of increased impulsive action, STN lesions decreased impulsive choice but dramatically impaired the acquisition of the autoshaping response. When the STN was lesioned after the establishment of autoshaping behaviour, lesioned subjects were more sensitive to the omission of reward, indicative of a reduction in the use of Pavlovian associations to control autoshaping performance. These results emphasize the importance of the STN in permitting conditioned stimulus-unconditioned stimulus associations to regulate goal-seeking, a function which may relate to the alterations in impulsive choice observed in the delay-discounting task. These data bear a striking similarity to those observed after lesions of the orbitofrontal cortex and are suggestive of an important role for corticosubthalamic connections in complex cognitive behaviour.     

Sugarplum fairies. Visual hallucinations

A 35-year-old woman with a history of early childhood encephalitis and a cerebrovascular accident during childbirth at 29 presented with visual hallucinations of two years' duration. A meningioma was removed from the right middle cranial fossa, and the visual hallucinations ceased. Visual hallucinations are complex phenomena which may arise through stimulation of the visual pathways at many levels. The case report is followed by discussion of various types of visual hallucinations and the theories and evidence regarding their pathophysiology.     

Palinopsia as sensory epileptic phenomenon

Visual perseveration (VP) is defined as persistence or recurrence of visual images, when the stimulus is no longer present. We report three patients with occipital cortical lesions in the right hemisphere and VP. Electroencephalography showed epileptic abnormalities in all cases. In one patient synchronous electroencephalic recordings during the onset of palinopsia - a subtype of VP - revealed, that VP was associated with a clear cut right occipital seizure with a secondary diffusion of the discharge over both hemispheres, which has not been reported in combination with the onset of palinopsia heretofore. In all three patients sensory seizures have to be considered as probable cause of VP.     

Visual perseveration: a new side effect of maprotiline

OBJECTIVE: The aim of this paper is to describe a case of visual perseveration including palinopsia during maprotiline therapy. METHOD: A single case report. RESULTS: The patient, a 56-year-old depressive man, suffered from visual perseveration during maprotiline therapy. The visual perseveration was dose-related and disappeared with reduction and cessation of the therapy. CONCLUSION: The present findings suggest that maprotiline can induce visual perseveration including palinopsia in some patients.     

Is recurrent perseveration a product of deafferented functional systems with otherwise normal post-activation decay rates?

Recent work in neuropsychology, clinical aphasiology and neuropharmacology have presented evidence that the causative substrates of recurrent perseveration in adults with aphasia are more recondite and subject to distinct interpretations than originally thought. This article will discuss and evaluate how various proposals from theory, from the clinic and from drug therapy interact and compete in the search for a cause or causes of recurrent perseveration.     

Random number generation during sleep deprivation: effects of caffeine on response maintenance and stereotypy

Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. Previous neuropsychological studies indicate that sleep deprivation causes impairments in prefrontal cortical function. Random number generation (RNG) is thought to provide a sensitive index of executive functions that rely on the prefrontal cortex. The present study tested the hypothesis that sleep deprivation would impair RNG and that caffeine would mitigate this impairment. Healthy young men (n = 21) participated in two 40-h sleep deprivations 1 week apart. During each sleep deprivation period subjects received either caffeine or placebo according to a randomized, double-blind cross-over design, and they completed an oral RNG task at 3-h intervals. Comparison of test sessions at analogous times of day revealed that sleep deprivation was associated with significant drops in the number of responses, a threefold increase in the percentage of rule violations, 59% greater response redundancy and a 20% increase in stereotypy of adjacent response pairs. Sleep deprivation did not consistently alter counting tendency. Caffeine ameliorated the decrease in the number of responses but did not mitigate other deficits in RNG that arose during sleep deprivation. These findings are consistent with prior reports of diminished vigilance and increased perseveration during extended wakefulness. They support the conclusion that caffeine preserves simple aspects of cognitive performance during sleep deprivation, whereas caffeine may not prevent detrimental effects of sleep deprivation on some complex cognitive functions.     

Influence of subthalamic deep brain stimulation versus levodopa on motor perseverations in Parkinson's disease

Patients with Parkinson's disease (PD) show impairment in generating random motor sequences reflecting a higher order motor deficit in set‐shifting and suppression of perseverative behavior. The impact of deep brain stimulation (DBS) of the subthalamic nucleus (STN) on motor perseverations has not yet been elucidated. In 35 patients with PD, we evaluated the effect of STN‐DBS and levodopa on motor perseverations using the Vienna perseveration task. The task was performed 6 months after implantation of stimulation electrodes in the following three conditions: Stimulation off/medication off (Stim OFF/Med OFF), Stim ON/Med OFF, and Stim OFF/Med ON. Perseverations were measured by redundancy of second order (R²) with higher values indicating more severe perseverations. ANCOVA analysis revealed that influence of STN‐DBS on R² significantly depended on R² severity during Stim OFF/Med OFF (F = 4.69, P = 0.035). Accordingly, we classified patients with PD into two groups based on the R² value during off treatment. In patients with mild perseveration (R² < 35) neither STN‐DBS nor levodopa changed perseverations. By contrast, in patients with severe perseveration (R² > 35), STN‐DBS significantly reduced R² by 9.7 ± 2.6 (P < 0.001) whereas levodopa had no impact (R² reduction 3.7 ± 1.6, P = 0.081). This demonstrates that STN‐DBS, by reducing motor perseveration, influences higher order aspects of motor behavior of patients with PD. © 2009 Movement Disorder Society     

Action-selection perseveration in young children: Advances of a dynamic model

This study presents an empirical test and dynamic model of perseverative limb selection in children of 14-, 24-, and 36-months old (N = 66 in total). In the experiment, children repeatedly grasped a spoon with a single hand. In two separate conditions, the spoon was presented either four times on their right side or four times on their left side. In both conditions, following this training, the spoon was presented on midline for two more trials. This setup enabled us to determine whether children's limb selection was influenced by their prior choices in the task (i.e., perseveration). Individual children's handedness was determined in a third condition consisting of nine object presentations (laterally or on midline). A dynamic model for limb selection is presented combining external input, motor memory, and preferences. The model was used to simulate the experiment and reproduced the results, including the age-related changes.