Aerobic exercise alters brain function and structure in Parkinson's disease a randomized controlled trial

Objective

Randomized clinical trials have shown that aerobic exercise attenuates motor symptom progression in Parkinson's disease, but the underlying neural mechanisms are unclear. Here, we investigated how aerobic exercise influences disease‐related functional and structural changes in the corticostriatal sensorimotor network, which is involved in the emergence of motor deficits in Parkinson's disease. Additionally, we explored effects of aerobic exercise on tissue integrity of the substantia nigra, and on behavioral and cerebral indices of cognitive control.

Methods

The Park‐in‐Shape trial is a single‐center, double‐blind randomized controlled trial in 130 Parkinson's disease patients who were randomly assigned (1:1 ratio) to aerobic exercise (stationary home trainer) or stretching (active control) interventions (duration = 6 months). An unselected subset from this trial (exercise, n = 25; stretching, n = 31) underwent resting‐state functional and structural magnetic resonance imaging (MRI), and an oculomotor cognitive control task (pro‐ and antisaccades), at baseline and at 6‐month follow‐up.

Results

Aerobic exercise, but not stretching, led to increased functional connectivity of the anterior putamen with the sensorimotor cortex relative to the posterior putamen. Behaviorally, aerobic exercise also improved cognitive control. Furthermore, aerobic exercise increased functional connectivity in the right frontoparietal network, proportionally to fitness improvements, and it reduced global brain atrophy.

Interpretation

MRI, clinical, and behavioral results converge toward the conclusion that aerobic exercise stabilizes disease progression in the corticostriatal sensorimotor network and enhances cognitive performance. ANN NEUROL 2022;91:203–216

[Phosphate Intoxication after Application of Enema--a Life-threatening Iatrogenic Complication]

INTRODUCTION

Enemas are used in pediatric patients with constipation. Retention of phosphate containing enemas with prolonged resorption or reduced renal elimination of phosphate can result in life-threatening hyperphosphatemia with subsequent lethal hypocalcemia and acidosis.

CASE PRESENTATION

We report the case of a 6-month-old child who received phosphate-containing enema to treat acute aggravation of constipation. The used enema here was not licensed for this age group. Phosphate intoxication resulted (phosphate 19.87 mmol/l) and presented like a sepsis. Hyperphosphatemia was treated by hemodialysis. A non-diagnosed Hirschsprung disease had led to prolonged resorption of phosphate containing enema and to an ileus and toxic megacolon that had to be operated.

CONCLUSION

Insufficient elimination of phosphate containing enema can result in lethal or life threatening hyperphosphatemia, hypocalcemia and metabolic acidosis. These can be treated efficaciously by hemodialysis. Because of the high risk of intoxication in using enemas containing phosphate in infants or in patients with gastrointestinal or renal comorbidities, physicians treating constipation should choose enemas without phosphate but with ingredients with lower risk like glycerol or sorbitol in this age group.

[Venous thromboembolism in adolescents associated with fourth-generation oral contraceptives]

Venous thromboembolism (VTE) is a rare, but feared adverse drug reaction of combined oral contraceptives. Modern oral contraceptives contain novel progestins, which are suspected of causing thrombotic events more frequently than well-known progestins. Drospirenone is one of those new fourth-generation progestins with antiandrogenic and antimineralocorticoid effects. Especially girls and young women do not only wish for contraception, but also for positive effects on skin and body weight. In the last decade, however, the safety of this progestin was often under discussion.A detailed literature search was conducted to obtain an overview of currently available data on the risk of VTE among girls and young women using drospirenone-containing contraceptives. It appears that drospirenone-containing contraceptives have a similar increase in risk as third-generation oral contraceptives and antiandrogens. Compared to second-generation contraceptives containing the progestin levonorgestrel there is an approximate 2-fold risk increase (1.0 to 2.8-fold) in women aged 10-55 years. Accurate data regarding the risk in the age group under 18 years are lacking. Nevertheless, the risk of VTE appears to be higher in young -women during the first months of treatment. Until more data for nov-el progestins are available and the safety profile is well defined well-studied second-generation oral contraceptives with low dose estrogen and better risk-benefit ratio should be preferred in young women. In any case, all patients should be comprehensively informed regarding the benefits and risks of each contraceptive method.

Reference frames for reach planning in human parietofrontal cortex

To plan a reaching movement, the brain must integrate information about the spatial goal of the reach with positional information about the selected hand. Recent monkey neurophysiological evidence suggests that a mixture of reference frames is involved in this process. Here, using 3T functional magnetic resonance imaging (fMRI), we tested the role of gaze-centered and body-centered reference frames in reach planning in the human brain. Fourteen human subjects planned and executed arm movements to memorized visual targets, while hand starting position and gaze direction were monitored and varied on a trial-by-trial basis. We further introduced a variable delay between target presentation and movement onset to dissociate cerebral preparatory activity from stimulus- and movement-related responses. By varying the position of the target and hand relative to the gaze line, we distinguished cerebral responses that increased for those movements requiring the integration of peripheral target and hand positions in a gaze-centered frame. Posterior parietal and dorsal premotor areas showed such gaze-centered integration effects. In regions closer to the primary motor cortex, body-centered hand position effects were found. These results suggest that, in humans, spatially contiguous neuronal populations operate in different frames of reference, supporting sensorimotor transformations according to gaze-centered or body-centered coordinates. The former appears suited for calculating a difference vector between target and hand location, whereas the latter may be related to the implementation of a joint-based motor command.

Spatial and effector processing in the human parietofrontal network for reaches and saccades

It is generally accepted that interactions between parietal and frontal cortices subserve the visuomotor processing for eye and hand movements. Here, we used a sequential-instruction paradigm in 3-T functional MRI to test the processing of effector and spatial signals, as well as their interaction, as a movement is composed and executed in different stages. Subjects prepared either a saccade or a reach following two successive visual instruction cues, presented in either order. One cue instructed which effector to use (eyes, right hand); the other signaled the spatial goal (leftward vs. rightward target location) of the movement. During the first phase of the prepared movement, after cueing of either goal or effector information, we found significant spatial goal selectivity but no effector specificity along the parietofrontal network. During the second phase of the prepared movement, when both goal and effector information were available, we found a large overlap in the neural circuitry involved in the planning of eye and hand movements. Gradually distributed along this network, we observed clear spatial goal selectivity and limited, but significant, effector specificity. Regions in the intraparietal sulcus and the dorsal premotor cortex were selective to both goal location and motor effector. Taken together, our results suggest that the relative weight of spatial goal and effector selectivity changes along the parietofrontal network, depending on the status of the movement plan.

Recent advances in functional neuroimaging of gait

In this review, we discuss the contribution of functional neuroimaging to the understanding of the cerebral control of gait in humans, both in healthy subjects and in patients with Parkinson's disease. We illustrate different approaches that have been used to address this issue, ranging from the imaging of actual gait performance to the study of initiation and imagery of gait. We also consider related approaches focused on specific aspects of gait, like those addressed by repetitive foot movements. We provide a critical discussion of advantages and disadvantages of each approach, emphasizing crucial issues to be addressed for a better understanding of the neural control of human gait.

Motor imagery of gait: a quantitative approach

Motor imagery (MI) is widely used to study cognitive aspects of the neural control of action. Prior studies were mostly centred on hand and arm movements. Recently a few studies have used imagery tasks to explore the neurophysiology of human gait, but it remains unclear how to ascertain whether subjects actually perform imagery of gait as requested. Here we describe a new experimental protocol to quantify imagery of gait, by behaviourally distinguishing it from visual imagery (VI) processes and by showing its temporal correspondence with actual gait. Fourteen young healthy subjects performed two imagery tasks and an actual walking (AW) task. During both imagery tasks subjects were sitting on a chair and faced a computer screen that presented photographs of walking trajectories. During one task (MI), subjects had to imagine walking along the walking trajectory. During the other task (VI), subjects had to imagine seeing a disc moving along the walking trajectory. During the AW task, subjects had to physically walk along the same walking trajectory as presented on the photographs during the imagery tasks. We manipulated movement distance by changing the length of the walking trajectory, and movement difficulty by changing the width of the walking trajectory. Subjects reported onset and offset of both actual and imagined movements with a button press. The time between the two button presses was taken as the imagined or actual movement time (MT). MT increased with increasing path length and decreasing path width in all three tasks. Crucially, the effect of path width on MT was significantly stronger during MI and AW than during VI. The results demonstrate a high temporal correspondence between imagined and AW, suggesting that MI taps into similar cerebral resources as those used during actual gait. These results open the possibility of using this protocol for exploring neurophysiological correlates of gait control in humans.

Integration of target and effector information in the human brain during reach planning

To plan a reaching movement, the brain must integrate information about the location of the target with information about the limb selected for the reach. Here, we applied rapid event-related 3-T fMRI to investigate this process in human subjects (n = 16) preparing a reach following two successive visual instruction cues. One cue instructed which arm to use; the other cue instructed the location of the reach target. We hypothesized that regions involved in the integration of target and effector information should not only respond to each of the two instruction cues, but should respond more strongly to the second cue due to the added integrative processing to establish the reach plan. We found bilateral regions in the posterior parietal cortex, the premotor cortex, the medial frontal cortex, and the insular cortex to be involved in target-arm integration, as well as the left dorsolateral prefrontal cortex and an area in the right lateral occipital sulcus to respond in this manner. We further determined the functional properties of these regions in terms of spatial and effector specificity. This showed that the posterior parietal cortex and the dorsal premotor cortex specify both the spatial location of a target and the effector selected for the response. We therefore conclude that these regions are selectively engaged in the neural computations for reach planning, consistent with the results from physiological studies in nonhuman primates.

No double-dissociation between optic ataxia and visual agnosia: multiple sub-streams for multiple visuo-manual integrations

The current dominant view of the visual system is marked by the functional and anatomical dissociation between a ventral stream specialised for perception and a dorsal stream specialised for action. The "double-dissociation" between visual agnosia (VA), a deficit of visual recognition, and optic ataxia (OA), a deficit of visuo-manual guidance, considered as consecutive to ventral and dorsal damage, respectively, has provided the main argument for this dichotomic view. In the first part of this paper, we show that the currently available empirical data do not suffice to support a double-dissociation between OA and VA. In the second part, we review evidence coming from human neuropsychology and monkey data, which cast further doubts on the validity of a simple double-dissociation between perception and action because they argue for a far more complex organisation with multiple parallel visual-to-motor connections: 1. A dorso-dorsal pathway (involving the most dorsal part of the parietal and pre-motor cortices): for immediate visuo-motor control--with OA as typical disturbance. The latest research about OA is reviewed, showing how these patients exhibit deficits restricted to the most direct and fast visuo-motor transformations. We also propose that mild mirror ataxia, consisting of misreaching errors when the controlesional hand is guided to a visual goal though a mirror, could correspond to OA with an isolated "hand effect". 2. A ventral stream-prefrontal pathway (connections from the ventral visual stream to pre-frontal areas, by-passing the parietal areas): for "mediate" control (involving spatial or temporal transpositions [Rossetti, Y., & Pisella, L. (2003). Mediate responses as direct evidence for intention: Neuropsychology of Not to-, Not now- and Not there-tasks. In S. Johnson (Ed.), Cognitive Neuroscience perspectives on the problem of intentional action (pp. 67-105). MIT Press.])--with VA as typical disturbance. Preserved visuo-manual guidance in patients with VA is restricted to immediate goal-directed guidance, they exhibit deficits for delayed or pantomimed actions. 3. A ventro-dorsal pathway (involving the more ventral part of the parietal lobe and the pre-motor and pre-frontal areas): for complex planning and programming relying on high representational levels with a more bilateral organisation or an hemispheric lateralisation--with mirror apraxia, limb apraxia and spatial neglect as representatives. Mirror apraxia is a deficit that affects both hands after unilateral inferior parietal lesion with the patients reaching systematically and repeatedly toward the virtual image in the mirror. Limb apraxia is localized on a more advanced conceptual level of object-related actions and results from deficient integrative, computational and "working memory" capacities of the left inferior parietal lobule. A component of spatial working memory has recently been revealed also in spatial neglect consecutive to lesion involving the network of the right inferior parietal lobule and the right frontal areas. We conclude by pointing to the differential temporal constraints and integrative capabilities of these parallel visuo-motor pathways as keys to interpret the neuropsychological deficits.

Task instructions influence the cognitive strategies involved in line bisection judgements: evidence from modulated neural mechanisms revealed by fMRI

Manual line bisection and a perceptual variant thereof (the Landmark test) are widely used to assess visuospatial neglect in neurological patients, but little is known about the cognitive strategies involved. In the Landmark test, one could explicitly compare the lengths of the left and right line segments; alternatively, one could compute the centre of mass of the display. We here investigate with functional MRI if these cognitive strategies modulate the neural mechanisms underlying judgements whether pre-transected horizontal lines are correctly bisected (the Landmark test) in normal volunteers. Functional neuroimaging (fMRI) was carried out in 12 healthy volunteers who judged: (a) whether the line segments on either side of the transection mark were of equal length, and (b) whether the transection mark was in the centre of the line. Line centre judgements were made significantly faster than line length comparisons. Increased neural activity common to both strategies was observed in inferior parietal lobes bilaterally and right temporooccipital cortex. Further activations, most likely reflecting general task demands like response selection and motor control, were found in the precentral gyrus bilaterally, supplementary motor area bilaterally, right anterior cingulate, right dorsolateral prefrontal cortex, cerebellar vermis, and right thalamus and right putamen. Explicit length comparisons (relative to line centre judgements) differentially activated left superior posterior parietal cortex, with a tendency toward activation of the equivalent area on the right, while the reverse comparison revealed differential activation in the lingual gyrus bilaterally and anterior cingulate cortex. The activations observed in inferior parietal cortex during task performance using either strategy are consistent with the results of lesion studies. The differential activation of superior posterior parietal cortex following length instructions suggests that explicit comparisons of spatial extent were implicated. The differential activation of bilateral occipital cortex following centre judgements suggests that the centre of a line is extracted at an early stage of visual processing.

Neural correlates of visuomotor associations. Spatial rules compared with arbitrary rules

A green button may be the target of a movement, or it may instruct the opening of an adjacent door. In the first case, its spatial configuration serves to guide the hand, whereas in the second case its colour allows a decision between alternative courses of action. This study contrasts these two categories of visuomotor transformation. Our goal was to test the hypothesis that visual information can influence the motor system through different, task-dependent pathways. We used positron emission tomography (PET) to measure human brain activity during the performance of two tasks requiring the transformation of visual stimuli to motor responses. The stimuli instructed either a spatially congruent grasping movement or an arbitrarily associated hand movement. The experimental design emphasised preparatory- over movement-related activity. We expected ventral parieto-precentral regions to contribute to the visuomotor transformations underlying grasping movements, and fronto-striatal circuitry to contribute to the selection of actions on the basis of associative rules. We found that selecting between alternative courses of action on the basis of associative rules specifically involved ventral prefrontal, striatal and dorsal precentral areas. Conversely, spatially congruent grasping movements evoked specific differential responses in ventral precentral and parietal regions. The results suggest that visual information can flow through the dorsal system to determine how actions are performed, but that fronto-striatal loops are involved in specifying which action should be performed in the current context.

Learning arbitrary visuomotor associations: temporal dynamic of brain activity

Primates can give behavioral responses on the basis of arbitrary, context-dependent rules. When sensory instructions and behavioral responses are associated by arbitrary rules, these rules need to be learned. This study investigates the temporal dynamics of functional segregation at the basis of visuomotor associative learning in humans, isolating specific learning-related changes in neurovascular activity across the whole brain. We have used fMRI to measure human brain activity during performance of two tasks requiring the association of visual patterns with motor responses. Both tasks were learned by trial and error, either before (visuomotor control) or during (visuomotor learning) the scanning session. Epochs of tasks performance ( approximately 30 s) were alternated with a baseline period over the whole scanning session ( approximately 50 min). We have assessed both linear and nonlinear modulations in the differential signal between tasks, independently from overall task differences. The performance indices of the visuomotor learning task smoothly converged onto the values of a steady-state control condition, according to nonlinear timecourses. Specific visuomotor learning-related activity has been found over a distributed cortical network, centred on a temporo-prefrontal circuit. These cortical time-modulated activities were supported early in learning by the hippocampal/parahippocampal complex, and late in learning by the basal ganglia system. These findings suggest the inferior temporal and the ventral prefrontal cortex are critical neural nodes for integrating perceptual information with executive processes.

The cerebellum and parietal cortex play a specific role in coordination: a PET study

The synthesis of complex, coordinated movements from simple actions is an important aspect of motor control. Lesion studies have revealed specific brain areas, particularly the cerebellum, to be essential for a variety of coordinated movements, and lend support to the view that the cerebellum is engaged in the integration of simple movements into compound ones. A PET study was therefore conducted to show which brain areas were active specifically during the coordinated execution of an arm and finger movement to visual targets. A two-by-two factorial design was employed, in which subjects either made arm or finger movements alone, made coordinated arm-finger movements, or made no movements. Voxels were identified where activity was significantly greater during the execution of coordinated movements than when movements were made alone and in which this increased activity could not be accounted for simply by the additive effects of the activations for each movement in isolation. The behavioral results showed that subjects coordinated arm and finger movements well during coordination scans. Coordination-specific activations were found in left anterior lobe and bilaterally in the paramedian lobules of the cerebellum. These are known to receive forelimb-specific spinocerebellar proprioceptive inputs that may be related to multijoint movements. The same areas also receive corticocerebellar afference from motor areas that may convey efference copy information to the cerebellum. Coordination-specific activations were also seen in areas of the posterior parietal cortex. The results provide direct evidence in healthy human subjects of specific cerebellar engagement during the coordination of movement, over and above the control of constituent movements.

Movement preparation and motor intention

This paper addresses the functional anatomy of movement representation. We have used associative visuomotor tasks with instructed delays to elicit motor preparatory activity. We regard such activity, when independent from transient stimulus-locked responses, as a likely candidate for the neural basis of movement representation (M. Jeannerod, The Cognitive Neuroscience of Action. Blackwell, Oxford, 1997). In a first event-related fMRI experiment, we found that preparing to move according to arbitrary visuomotor associations relies not only on parietofrontal circuitry, but also on portions of the posterior superior temporal sulcus. In a separate behavioral experiment, we discarded the hypothesis that such activities were confounded by working memory processes. In a second imaging experiment, we have further defined the relative contributions of these parietal, premotor, and temporal areas to the preparatory process and their involvement in motor representations. We conclude that posterior parietal cortex is interested in evaluating the potential motor significance of sensory stimuli, irrespectively of the likelihood of providing a response ("motor intention"). Conversely, preparatory activity in frontal premotor regions appears to be a function of the probability of a subsequent movement. Finally, on the basis of the present and published data, we suggest that posterior temporal cortex might be involved in the extraction of contextual and intentional cues during goal-oriented behavior.

Contrasting the dorsal and ventral visual systems: guidance of movement versus decision making

It is widely accepted that the ventral visual pathways are involved in the identification of objects and the dorsal visual pathways in the visual guidance of reaching and grasping movements. But there are also situations, such as in a choice reaction time task, in which the subjects must select between actions on the basis of visual cues. This paper uses brain imaging to explore the pathways that are involved. Studies using PET and fMRI show that when subjects learn which actions are appropriate given the visual context, there are learning-related increases in the inferotemporal cortex and the ventral prefrontal cortex to which it projects. An event-related fMRI study shows that the activity in the inferotemporal cortex is time-locked to the presentation of the visual cue and the activity in the ventral prefrontal cortex to the response. Finally two PET studies directly compare the dorsal and ventral systems. In the second of these the subjects either move their finger on a moving target or identify the direction of movement and press one of two buttons to report the direction. When the subjects report the direction there is activity in the middle temporal gyrus and ventral prefrontal cortex. It is suggested that, when subjects must consciously identify the context and decide on the appropriate action, ventral pathways are involved.

Subcortical correlates of craving in recently abstinent alcoholic patients

OBJECTIVE

This study investigated functional cerebral correlates of craving in alcoholic patients and examined the state/trait characteristics of the regional cerebral network implicated in craving.

METHOD

Functional magnetic resonance imaging (fMRI) was used to map cerebral response elicited by ethanol odor in 10 male patients with alcohol dependence who had undergone detoxification and 10 matched nonpatients. After 3 weeks, during which the patients underwent standardized behavioral therapy with psychopharmacological intervention, all subjects were studied a second time with fMRI to evaluate the effects of therapy on the functional cerebral correlates of craving.

RESULTS

In the alcoholic patients, cue-induced craving before treatment elicited activation primarily in the subcortical-limbic region of the right amygdala/hippocampal area and in the cerebellum. After treatment, activation was found in the superior temporal sulcus, while subcortical or cerebellar participation was no longer present. Comparison subjects showed no comparable amygdala or cerebellar activation during ethanol stimulation and demonstrated no change in activation pattern between measurements.

CONCLUSIONS

This investigation points to state-dependent neurobiological correlates of cue-induced craving in alcoholic patients and suggests that these correlates can be influenced by therapeutic interventions. The presence of emotional aspects of craving is suggested by amygdala activation.

'Where' depends on 'what': a differential functional anatomy for position discrimination in one- versus two-dimensions

Line bisection is widely used as a clinical test of spatial cognition in patients with left visuospatial neglect after right hemisphere lesion. Surprisingly, many neglect patients who show severe impairment on marking the center of horizontal lines can accurately mark the center of squares. That these patients with left neglect are also typically poor at judging whether lines are correctly prebisected implies that the deficit can be perceptual rather than motoric. These findings suggest a differential neural basis for one- and two-dimensional visual position discrimination that we investigated with functional neuroimaging (fMRI). Normal subjects judged whether, in premarked lines or squares, the mark was placed centrally. Line center judgements differentially activated right parietal cortex, while square center judgements differentially activated the lingual gyrus bilaterally. These distinct neural bases for one- and two-dimensional visuospatial judgements help explain the observed clinical dissociations by showing that as a stimulus becomes a better, more 'object-like' gestalt, the ventral visuoperceptive route assumes more responsibility for assessing position within the object.

Learning- and expectation-related changes in the human brain during motor learning

We have studied a simple form of motor learning in the human brain so as to isolate activity related to motor learning and the prediction of sensory events. Whole-brain, event-related functional magnetic resonance imaging (fMRI) was used to record activity during classical discriminative delay eyeblink conditioning. Auditory conditioned stimulus (CS+) trials were presented either with a corneal airpuff unconditioned stimulus (US, paired), or without a US (unpaired). Auditory CS- trials were never reinforced with a US. Trials were presented pseudorandomly, 66 times each. The subjects gradually produced conditioned responses to CS+ trials, while increasingly differentiating between CS+ and CS- trials. The increasing difference between hemodynamic responses for unpaired CS+ and for CS- trials evolved slowly during conditioning in the ipsilateral cerebellar cortex (Crus I/Lobule HVI), contralateral motor cortex and hippocampus. To localize changes that were related to sensory prediction, we compared trials on which the expected airpuff US failed to occur (Unpaired CS+) with trials on which it occurred as expected (Paired CS+). Error-related signals in the contralateral cerebellum and somatosensory cortex were seen to increase during learning as the sensory prediction became stronger. The changes seen in the ipsilateral cerebellar cortex may be due either to the violations of sensory predictions, or to learning-related increases in the excitability of cerebellar neurons to presentations of the CS+.

Specialisation within the prefrontal cortex: the ventral prefrontal cortex and associative learning

This paper provides evidence that the ventral prefrontal cortex plays a role in the learning of tasks in which subjects must learn to associate visual cues and responses. Imaging with both positron-emission tomography (PET) and functional magnetic-resonance imaging (fMRI) reveals learning-related increases in activity when normal subjects learn visual associative tasks. Evidence is also presented from an event-related fMRI study that activity in this area is time-locked both to the presentation of the visual stimuli and also to the time of the motor response. Finally, it is shown in a study of monkeys that removal of the ventral prefrontal area 12 (including 45 A) impairs the ability of monkeys to relearn a visual associative task (visual matching), even though there were no demands on working memory. It is, therefore, proposed that the ventral prefrontal cortex constitutes part of the circuitry via which associations are formed between visual cues and the actions or choices that they specify. On the basis of the existing anatomical and electrophysiological data, it is argued that the prefrontal cortex is the only area that can represent cues, responses and outcomes.

The prefrontal cortex: response selection or maintenance within working memory?

It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.

Prefrontal-basal ganglia pathways are involved in the learning of arbitrary visuomotor associations: a PET study

Primates can learn to associate sensory cues with particular movements according to arbitrary rules. We used positron emission tomography (PET) to study the neural network involved in learning such arbitrary associations by trial and error. Ten subjects were scanned at four different stages of learning a visuomotor conditional task (VC). The subjects were required to associate four different visual patterns, presented one at a time, with four different finger movements. Scan 1 was acquired during initial learning. Scans 2, 3 and 4 were performed after further interscan training periods of 1, 3 and 5 min. In order to control for non-specific time effects that could have confounded the learning-related rCBF changes, we also acquired four sensory-matched control scans, in which no movements were performed. In order to evaluate changes over time that were specific to learning the association of visual cues with movements, we acquired four scans during the learning of a motor sequence task. The statistical model tested with SPM considered both main effects of tasks and task x time interactions independently for each of the three experimental conditions. The right lingual gyrus and the left parahippocampal cortex increased their activity over scans in the VC task as compared to the sensory control. The right inferior frontal sulcus, the body of the caudate nucleus and a left cingulate motor area were specifically implicated in learning the VC task, showing task x time interactions with the motor sequence task. These findings suggest that the learning process involves a distributed network in the ventral extrastriate and prefrontal cortex, in association with the basal ganglia and the parahippocampal gyrus.

A functional anatomy of anticipatory anxiety

Anticipatory anxiety is a complex combination of a future-oriented cognitive state, negative affect, and autonomic arousal. A dual-task paradigm of anticipation of electric shocks and a motor-learning task was used to examine the changes in neural patterns of activation associated with modulation of the cognitive state in anxiety by a distracting motor task. We used positron emission tomography (PET) and 15O-water to measure regional cerebral blood flow (rcbf) in 10 healthy male volunteers. A 2x2 factorial design-(shock vs no shock) x (low vs high distraction) was used with three scans per condition. Twelve PET scans were performed on each subject. In six of these scans, subjects were given electric shocks. In all scans, subjects also simultaneously performed a motor repetition (low distraction) or learning (high distraction) task. Galvanic skin conductance (GSR), Spielberger State and Trait Anxiety Inventory (STAI), and self-report data were also collected. In comparisons between the shock and no-shock conditions, the main finding was of increased rcbf in the left insula (-38,8,8) (z = 4.85, P<0.05 corrected) and a homologous area in the right insula at a lower threshold (z =3.20, P = 0.001 uncorrected). Other areas activated were the right superior temporal sulcus, left fusiform, and left anterior cingulate. Using the STAI-state scores as a covariate of interest, significant correlations with rCBF were seen in the left orbitofrontal cortex, left insula, and left anterior cingulate cortex. There was no significant distraction effect as measured by the STAI, self-report, GSR response or interactional analysis of the PET data. These findings support the role of paralimbic structures as neural substrates of anticipatory anxiety. The failure to demonstrate behavioral and neurophysiological changes with the distractor task may reflect the modest increases in anxiety with the shock, the relatively simple distractor task, and small sample size.

How do visual instructions influence the motor system?

The paper distinguishes the use of visual cues to guide reaching and grasping, and the ability to learn to associate arbitrary sensory cues with movements. Using positron emission tomography (PET), we have shown that the arbitrary association of visual cues and movements involves the ventral visual system (prestriate, inferotemporal and ventral prefrontal cortex), the basal ganglia and the dorsal premotor cortex. Using functional magnetic resonance imaging (fMRI), we have shown that the evoked haemodynamic responses in the ventral visual system are time-locked to the presentation of the visual cues, that the response in the motor cortex is locked to the time of response, and that the response in the dorsal premotor cortex shows cuerelated, movement-related and set-related components. Using PET we have shown that there are learning-related changes in activation in both the ventral prestriate cortex and the basal ganglia (globus pallidus) when subjects learn a visuomotor associative task. We argue that the basal ganglia may act as a flexible system for learning the association of sensory cues and movements.

Signal-, set- and movement-related activity in the human brain: an event-related fMRI study

Electrophysiological studies on monkeys have been able to distinguish sensory and motor signals close in time by pseudorandomly delaying the cue that instructs the movement from the stimulus that triggers the movement. We have used a similar experimental design in functional magnetic resonance imaging (fMRI), scanning subjects while they performed a visuomotor conditional task with instructed delays. One of four shapes was presented briefly. Two shapes instructed the subjects to flex the index finger; the other two shapes coded the flexion of the middle finger. The subjects were told to perform the movement after a tone. We have exploited a novel use of event-related fMRI. By systematically varying the interval between the visual and acoustic stimuli, it has been possible to estimate the significance of the evoked haemodynamic response (EHR) to each of the stimuli, despite their temporal proximity in relation to the time constant of the EHR. Furthermore, by varying the phase between events and image acquisition, we have been able to achieve high temporal resolution while scanning the whole brain. We dissociated sensory and motor components of the sensorimotor transformations elicited by the task, and assessed sustained activity during the instructed delays. In calcarine and occipitotemporal cortex, the responses were exclusively associated with the visual instruction cues. In temporal auditory cortex and in primary motor cortex, they were exclusively associated with the auditory trigger stimulus. In ventral prefrontal cortex there were movement-related responses preceded by preparatory activity and by signal-related activity. Finally, responses associated with the instruction cue and with sustained activity during the delay period were observed in the dorsal premotor cortex and in the dorsal posterior parietal cortex. Where the association between a visual cue and the appropriate movement is arbitrary, the underlying visuomotor transformations are not achieved exclusively through frontoparietal interactions. Rather, these processes seem to rely on the ventral visual stream, the ventral prefrontal cortex and the anterior part of the dorsal premotor cortex.

The time course of changes during motor sequence learning: a whole-brain fMRI study

There is a discrepancy between the results of imaging studies in which subjects learn motor sequences. Some experiments have shown decreases in the activation of some areas as learning increased, whereas others have reported learning-related increases as learning progressed. We have exploited fMRI to measure changes in blood oxygen leve-dependent (BOLD) signal throughout the course of learning. T2*-weighted echo-planar images were acquired over the whole brain for 40 min while the subjects learned a sequence eight moves long by trial and error. The movements were visually paced every 3.2 s and visual feedback was provided to the subjects. A baseline period followed each activation period. The effect due to the experimental conditions was modeled using a square-wave function, time locked to their occurrence. Changes over time in the difference between activation and baseline signal were modeled using a set of polynomial basis functions. This allowed us to take into account linear as well as nonlinear changes over time. Low-frequency changes over time common to both activation and baseline conditions (and thus not learning related) were modeled and removed. Linear and nonlinear changes of BOLD signal over time were found in prefrontal, premotor, and parietal cortex and in neostriatal and cerebellar areas. Single-unit recordings in nonhuman primates during the learning of motor tasks have clearly shown increased activity early in learning, followed by a decrease as learning progressed. Both phenomena can be observed at the population level in the present study.

Influence of object position and size on human prehension movements

Prehension movements of the right hand were recorded in normal subjects using a computerized motion analyzer. The kinematics and the spatial paths of markers placed at the wrist and at the tips of the index finger and thumb were measured. Cylindrical objects of different diameters (3, 6, 9 cm) were used as targets. They were placed at six different positions in the workspace along a circle centered on subject's head axis. The positions were spaced by 10 degrees starting from 10 degrees on the left of the sagittal axis, up to 40 degrees on the right. Both the transport and the grasp components of prehension were influenced by the distance between the resting hand position and the object position. Movement time, time to peak velocity of the wrist and time to maximum grip aperture varied as a function of distance from the object, irrespective of its size. The variability of the spatial paths of wrist and fingers sharply decreased during the phase of the movement prior to contact with the object. This indicates that the final position of the thumb and the index finger is a controlled parameter of visuomotor transformation during prehension. The orientation of the opposition axis (defined as the line connecting the tips of the thumb and the index finger at the end of the movement) was measured. Several different frames of reference were used. When an object-centered frame was used, the orientation of the opposition axis was found to change by about 10 degrees from one object position to the next. By contrast, when a body-centered frame was used (with the head or the forearm as a reference), this orientation was found to remain relatively invariant for different object positions and sizes. The degree of wrist flexion was little affected by the position of the object. This result, together with the invariant orientation of the opposition axis, shows that prehension movements aimed at cylindrical objects are organized so as to minimize changes in posture of the lower arm.

Tactile input of the hand and the control of reaching to grasp movements

The role of tactile information of the hand in the control of reaching to grasp movements was investigated. The kinematics of both reaching (or transport) and grasp components were studied in healthy subjects in two experimental conditions. In one condition (control condition) subjects were required to reach and grasp an object that could have two sizes and that could be located at two distances from the viewer. In the other condition (anaesthesia condition) the same movements were executed, but anaesthesia was provided to the subjects' fingertips. In both conditions vision of the hand was prevented during movement. Anaesthesia affected mainly the kinematics of the first phase of grasping, that is, the finger-opening phase. This phase was lengthened and maximal finger aperture increased. In contrast, the duration of the successive phase (finger-closure) was poorly modified. The reaching component was also impaired by anaesthesia. Although the total extent of hand path and the spatial relations between the finger aperture and closure phases did not change between the two conditions, hand path variability increased. This occurred during transport deceleration phase and after the increase in variability of finger path. In addition, the whole movement was slowed down. The results of the present experiment suggest that tactile signals at the beginning and at the end of movement can be used to compute grasp time and to optimise grasp temporal parameters. Alternatively, signals from tactile receptors can be involved in encoding the position sense of the fingers. When this input is lacking, the control of grasp and in particular that of finger-opening phase can be impaired. Finally, the effect of the grasp impairment on the reaching component supports the notion that the coordination between reaching and grasping involves the whole temporal course of the two components.

Eye position tunes the contribution of allocentric and egocentric information to target localization in human goal-directed arm movements

Subjects were required to point to the distant vertex of the closed and the open configurations of the Müller-Lyer illusion using either their right hand (experiment 1) or their left hand (experiment 2). In both experiments the Müller-Lyer figures were horizontally presented either in the left or in the right hemispace and movements were executed using either foveal or peripheral vision of the target. According to the illusion effect, subjects undershot and overshot the vertex location of the closed and the open configuration, respectively. The illusion effect decreased when the target was fixated and when the stimulus was positioned in the right hemispace. These results confirm the hypothesis that both egocentric and allocentric information are combined in order to encode target position in space. When movements are directed to foveal targets, decreasing effects of allocentric cues, as shown by decreasing the illusion effect, could be due to enhanced efficiency of the egocentric system. That is, information on eye position when target is fixated can be used to precisely establish its spatial relations with the body. In addition, a more accurate analysis of allocentric information is hypothesized when the target is positioned in the left hemispace. In other words, our data confirm the notion that the right cerebral hemisphere is involved in space representation.

Visual pathways for object-oriented action and object recognition: functional anatomy with PET

The purpose of this study was to identify the functional anatomy of the mechanisms involved in visually guided prehension and in object recognition in humans. The cerebral blood flow of seven subjects was investigated by positron emission tomography. Three conditions were performed using the same set of stimuli. In the 'grasping' condition, subjects were instructed to accurately grasp the objects. In the 'matching' condition, subjects were requested to compare the shape of the presented object with that of the previous one. In the 'pointing' condition (control), subjects pointed towards the objects. The comparison between grasping and pointing showed a regional cerebral blood flow (rCBF) increase in the anterior part of the inferior parietal cortex and part of the posterior parietal cortex. The comparison between grasping and matching showed an rCBF increase in the cerebellum, the left frontal cortex around the central sulcus, the mesial frontal cortex and the left inferior parietal cortex. Finally, the comparison between matching and pointing showed an rCBF increase in the right temporal cortex and the right posterior parietal cortex. Thus object-oriented action and object recognition activate a common posterior parietal area, suggesting that some kind of within-object spatial analysis was processed by this area whatever the goal of the task.

Differential influence of the visual framework on end point accuracy and trajectory specification of arm movements

In this study the influence of visual scene on both arm end point accuracy and spatial path kinematics was evaluated. Eight subjects, immersed in a virtual environment, were required to point to one of ten targets located at two distances and in five directions. Targets were presented in frameworks of different complexity. The simplest framework was constituted by a uniform background, the most complex framework was constituted by a perspective-arranged grid. In the other two conditions it consisted of lines having a direction parallel to either the subject's sagittal or frontal body axis. Movements were executed without vision of both target and framework. The results showed that pointing movements were hypometric in all conditions. No difference in end point localization was observed between movements executed after presentation of the simplest and the most complex scenes. However, hypometria significantly increased when the scene was formed by lines parallel to the subject's sagittal axis. Visual information on the scene was also used to specify hand path parameters. Trajectory curvature increased with decreasing complexity of the framework. Correspondingly, the pointing kinematics varied. Taken together, these results suggest that visual analysis of cues surrounding the target can influence both target localisation and hand path planning. However, scene complexity is directly related only to determining trajectory curvature. We conclude that planning an arm movement consists of at least two processes: target localisation and hand path specification. Environmental visual cues forming the scene are taken into account differently during the two processes.

Visual illusion and action

The role of allocentric cues on movement control was investigated in the present study. Pointing movements directed to the more distant vertex of closed and open configurations of the Muller-Lyer illusion, as well as to the vertex of control lines, were studied in four experimental conditions. In the first (full-vision condition) subjects saw both stimulus and their hand before and during movement, in the second (non-visual feedback condition) they saw the stimulus, but not their hand during movement. In the two remaining conditions (no-vision conditions) vision of the scene and the hand was precluded. Pointing was executed 0 sec (no vision 0 sec delay condition) or 5 sec (no-vision 5 sec delay condition) after the light was switched off. The Muller-Lyer illusion affected pointing kinematics with respect to the control lines. Subjects undershot and overshot the vertex location, respectively, of the closed and open configuration. Correspondingly, the entire kinematics were changed. The main result was, however, a gradually increasing effect of the perceptual illusion when pointing was executed from memory compared to the full-vision condition. These data are discussed according to the hypothesis that the system underlying visual perception in the allocentric frame of reference and that involved in motor action can functionally interact. The strength of this interaction depends upon the efficiency of the egocentric frame of reference by which motor actions are constructed.

On orienting the hand to reach and grasp an object

Subjects were required to reach and grasp a parallelepiped, the position, orientation and size of which were varied. The kinematics of reaching and grasping movements was studied in full vision and in no vision conditions. Both direction and movement amplitude of reaching were affected by object orientation. Conversely, both the time course of finger axis orientation and the angular displacement of the hand at wrist were influenced by object position. These results were not modified by the absence of visual control. Finger aperture during grasping was affected by both object size and orientation. This latter result was not due to a distorted size perception, as shown by a control matching experiment. Taken together, the results of the present study suggest the integration between distal and proximal components during reaching and grasping.

Unconscious updating of grasp motor program

Grasp modification during prehension movements was studied in response to slight variations of somesthetic information about object size. Three experiments were carried out. In experiment 1 eight subjects were required to reach and grasp an object whose size could either increase or decrease, whereas its visual image remained unmodified. The object size was changed during the experiment with uninformed subjects after a block of trials during which visual and somesthetic information were congruent. At the end of the experiment subjects were required to reproduce the size of the object with their fingers (matching test). Results showed that maximal grip aperture during prehension as well as finger aperture in the matching test were modified according to variation in object size, although no subject realized that the object had changed during the experiment. Grasp time was also altered by object size change. Greater and earlier adaptation in maximal grip aperture, as well as perturbation of grasp time, were observed for decrease than for increase in object size. However, complete compensation was never reached for both parameters. Constant confidence in vision could have prevented both complete compensation and conscious detection of object change. This was investigated in two additional experiments. In experiment 2 visual information was made unreliable by informing subjects about variation in grasped object size. This led to greater and earlier modification in maximal grip aperture than in experiment 1. Grasp time was kept almost constant regardless of size variation. In experiment 3 vision of the stimulus was prevented and no information on change in object size was given to subjects. The results of experiment 3 were similar to those of experiment 1, although modification in maximal grip aperture was larger for increase in object size. Correspondingly, grasp time was more affected by increase than by decrease in object size. The results of the three experiments suggest that kinematic parameters usually considered as dependent on object properties, such as maximal grip aperture, were modified in order to compensate perturbation of temporal parameters. This modification induced a "pragmatic" knowledge of object size (as showed by the results of the matching test), although awareness was not reached.

Pattern of desynchronized sleep during deprivation and recovery induced in the rat by changes in ambient temperature

The pattern of desynchronized sleep (DS) occurrence in the rat was studied during exposure to an ambient temperature (Ta) of 0 degrees C for 48 h and during a 12 h recovery period at laboratory Ta (23 degrees C) following the first and second 24 h of cold exposure. The exposure to low Ta induces a DS deprivation which is followed, during recovery, by a clear DS rebound. Both the decrease and the following increase in the amount of DS are due to changes in the frequency rather than in the duration of DS episodes. The frequency distribution of the intervals between the end of one DS episode and the beginning of the next (DS interval) has shown that two populations of DS intervals exist, i.e. short DS intervals (</=3 min) and long DS intervals (>3 min). On the basis of this, two types of DS episodes have been identified: the 'single DS episode', which is both preceded and followed by a long DS interval, and the 'sequential DS episode', which is a DS episode occurring within a cluster or a sequence of DS episodes and is characteristically separated by short DS intervals. The occurrence of such sequential DS episodes in a 'DS cluster', allows a high amount of DS to occur without increasing the duration of the DS episode. DS clusters are repressed during cold exposure, when the DS drive is counteracted by the need to thermoregulate, and enhanced during recovery, when the DS drive is unrestrained. In contrast, the occurrence of single DS episodes is much less affected by such different experimental conditions.

The role of proprioception in the control of prehension movements: a kinematic study in a peripherally deafferented patient and in normal subjects

In this study we investigated the role of proprioception in the control of prehension movements, with particular reference to the grasp component. Grasp and transport kinematics were studied in a peripherally deafferented patient and in five healthy subjects. Two experiments were carried out: the prehension experiment and the grasp perturbation experiment. In the prehension experiment both the patient and the control subjects were required to reach and grasp three objects of different size, located at three different distances, both with and without visual feedback. In the grasp perturbation experiment a mechanical perturbation was applied to the fingers during prehension movements, again executed with and without visual feedback. In the prehension experiment temporal parameters of the patient's movements were generally slowed, with greater variability on some measures. However, over the first phase of the movement the pattern of the patient's hand opening and transport acceleration, scaled to object size and distance, was the same as that of controls, both with and without visual feedback. On the contrary, during the final phase of the movement (the finger closure phase and deceleration) the patient's performance differed significantly from the controls. These phases were abnormally lengthened and frequent movement adjustments were observed. In the grasp perturbation experiment the patient was not able to compensate for the perturbations applied to the fingers, even with visual feedback. The data allowed us to investigate also the respective contribution of proprioception and of vision of the hand in the control of prehension. We compared prehension kinematics in two conditions: (a) with visual but no proprioceptive feedback (in the patient) and (b) with proprioceptive but no visual feedback (in the controls). In both experiments proprioceptive control was more efficient than visual control. The results of this study are interpreted in favour of the strict dependence of prehension control on proprioception. The first phase of the movement, however, can be appropriately planned and executed without the necessity of either proprioceptive or visual information about the hand.