Biomedical subjects

Ivan Toni

Publications and source records attributed to Ivan Toni.

14 recordsLinked to original sources

PubMed2006

Online maintenance of sensory and motor representations: effects on corticospinal excitability.

Flexible behavior requires the ability to delay a response until it is appropriate. This can be achieved by holding either a sensory or a motor representation online. Here we assess whether maintenance of sensory or motor material drives the motor system to different functional states, as indexed by alterations of corticospinal excitability. We used single-pulse TMS to measure corticospinal excitability evoked during the delay period of a novel paradigm in which task contingencies, rather than explicit verbal instructions, induced participants to use either sensory or motor codes to solve a delay-nonmatch-to-sample (DNMS) task. This approach allowed us to probe the state of the motor system while the participants were retaining either sensory or motor codes to cross the delay period, rather than the control of short-term storage driven by verbal instructions. When participants could prepare the movement in advance (preparation trials), the excitability of the motor cortex contralateral to the moving hand increased, whereas the excitability of the ipsilateral motor cortex decreased. The increase in excitability was confined to the prime mover, whereas the decrease in excitability extended to cortical territories controlling muscles unrelated to the response. Crucially, these changes in excitability were evoked only during preparation trials and not during trials in which subjects needed to maintain sensory items online (memory trials). We infer that short-term storage of sensory information and preparation of motor responses have differential and specific access to the output stage of the motor system.

Adult↗

PubMed2006

Posture influences motor imagery: an fMRI study.

Motor imagery is widely used to study cognitive aspects of the neural control of action. However, what is exactly simulated during motor imagery is still a matter of debate. On the one hand, it is conceivable that motor imagery is an embodied cognitive process, involving a simulation of movements of one's own body. The alternative possibility is that, although motor imagery relies on knowledge of the motor processes, it does not entail an actual motor simulation that is influenced by the physical configuration of one's own body. Here we discriminate between these two hypotheses, in the context of an established motor imagery task: laterality judgments of rotated hand drawings. We found that reaction times of hand laterality judgments followed the biomechanical constraints of left or right hand movements. Crucially, the position of subjects' own left and right arm influenced laterality judgments of left and right hands. In neural terms, hand laterality judgments activated a parieto-frontal network. The activity within this network increased with increasing biomechanical complexity of the imagined hand movements, even when the amount of stimulus rotation was identical. Moreover, activity in the intraparietal sulcus was modulated by subjects' own hand position: a larger incongruence in orientation between the subjects' hand and the stimulus hand led to a selective increase in intraparietal activity. Our results indicate that motor imagery generates motor plans that depend on the current configuration of the limbs. This motor plan is calculated by a parieto-frontal network. Within this network, the posterior parietal cortex appears to incorporate proprioceptive information related to the current position of the body into the motor plan.

Adult↗

PubMed2006

Information processing in human parieto-frontal circuits during goal-directed bimanual movements.

It is known that, in macaques, movements guided by somatosensory information engage anterior parietal and posterior precentral regions. Movements performed with both visual and somatosensory feedback additionally activate posterior parietal and anterior precentral areas. It remains unclear whether the human parieto-frontal circuits exhibit a similar functional organization. Here, we employed a directional interference task requiring a continuous update of sensory information for the on-line control of movement direction, while brain activity was measured by functional magnetic resonance imaging (fMRI). Directional interference arises when bimanual movements occur along different directions in joint space. Under these circumstances, the presence of visual information does not substantially alter performance, such that we could vary the amount and type of sensory information used during on-line guidance of goal-directed movements without affecting motor output. Our results confirmed that in humans, as in macaques, movements guided by somatosensory information engages anterior parietal and posterior precentral regions, while movements performed with both visual and somatosensory information activate posterior parietal and anterior precentral areas. We provide novel evidence on how the interaction of specific portions of the dorsal parietal and precentral cortex in the right hemisphere might generate spatial representations by integrating different sensory modalities during goal-directed movements.

Adult↗

PubMed2006

Cerebral changes during performance of overlearned arbitrary visuomotor associations.

The posterior parietal cortex (PPC) is known to be involved in the control of automatic movements that are spatially guided, such as grasping an apple. We considered whether the PPC might also contribute to the performance of visuomotor associations in which stimuli and responses are linked arbitrarily, such as producing a certain sound for a typographical character when reading aloud or pressing pedals according to the color of a traffic light when driving a motor vehicle. The PPC does not appear to be necessary for learning new arbitrary visuomotor associations, but with extensive training, the PPC can encode nonspatial sensory features of task-relevant cues. Accordingly, we have tested whether the contributions of the PPC might become apparent once arbitrary sensorimotor mappings are overlearned. We have used functional magnetic resonance imaging to measure cerebral activity while subjects were learning novel arbitrary visuomotor associations, overlearning known mappings, or attempting to learn frequently changing novel mappings. To capture the dynamic features of cerebral activity related to the learning process, we have compared time-varying modulations of activity between conditions rather than average (steady-state) responses. Frontal, striatal, and intraparietal regions showed decreasing or stable activity when subjects learned or attempted to learn novel associations, respectively. Importantly, the same frontal, striatal, and intraparietal regions showed time-dependent increases in activity over time as the mappings become overlearned, i.e., despite time-invariant behavioral responses. The automaticity of these mappings predicted the degree of intraparietal changes, indicating that the contribution of the PPC might be related to a particular stage of the overlearning process. We suggest that, as the visuomotor mappings become robust to interference, the PPC may convey relevant sensory information toward the motor cortex. More generally, our findings illustrate how rich cerebral dynamics can underlie stable behavior.

Adult↗

PubMed2006

Comparable mechanisms for action and language: neural systems behind intentions, goals, and means.

In this position paper we explore correspondence between neural systems for language and action starting from recent electrophysiological findings on the roles of posterior and frontal areas in goal-directed grasping actions. The paper compares the perceptual and motor organization for action and language, and discusses similarities between the impairments of apraxic and aphasic patients. Furthermore, based on the anatomical connectivity of Brodmann areas (BA) 44 and 45 separate functional roles are proposed for the two constituent parts of Broca's area. The final part of the paper includes a discussion on the role of BA 44 and neighboring areas in sequential processing for action and language.

Brain↗

PubMed2005

Neural dynamics of error processing in medial frontal cortex.

Adaptive behavior requires an organism to evaluate the outcome of its actions, such that future behavior can be adjusted accordingly and the appropriate response selected. During associative learning, the time at which such evaluative information is available changes as learning progresses, from the delivery of performance feedback early in learning to the execution of the response itself during learned performance. Here, we report a learning-dependent shift in the timing of activation in the rostral cingulate zone of the anterior cingulate cortex from external error feedback to internal error detection. This pattern of activity is seen only in the anterior cingulate, not in the pre-supplementary motor area. The dynamics of these reciprocal changes are consistent with the claim that the rostral cingulate zone is involved in response selection on the basis of the expected outcome of an action. Specifically, these data illustrate how the anterior cingulate receives evaluative information, indicating that an action has not produced the desired result.

Adaptation, Psychological↗

PubMed2005

Gray matter volume reduction in the chronic fatigue syndrome.

The chronic fatigue syndrome (CFS) is a disabling disorder of unknown etiology. The symptomatology of CFS (central fatigue, impaired concentration, attention and memory) suggests that this disorder could be related to alterations at the level of the central nervous system. In this study, we have used an automated and unbiased morphometric technique to test whether CFS patients display structural cerebral abnormalities. We mapped structural cerebral morphology and volume in two cohorts of CFS patients (in total 28 patients) and healthy controls (in total 28 controls) from high-resolution structural magnetic resonance images, using voxel-based morphometry. Additionally, we recorded physical activity levels to explore the relation between severity of CFS symptoms and cerebral abnormalities. We observed significant reductions in global gray matter volume in both cohorts of CFS patients, as compared to matched control participants. Moreover, the decline in gray matter volume was linked to the reduction in physical activity, a core aspect of CFS. These findings suggest that the central nervous system plays a key role in the pathophysiology of CFS and point to a new objective and quantitative tool for clinical diagnosis of this disabling disorder.

Adult↗

PubMed2005

Neural topography and content of movement representations.

We have used implicit motor imagery to investigate the neural correlates of motor planning independently from actual movements. Subjects were presented with drawings of left or right hands and asked to judge the hand laterality, regardless of the stimulus rotation from its upright orientation. We paired this task with a visual imagery control task, in which subjects were presented with typographical characters and asked to report whether they saw a canonical letter or its mirror image, regardless of its rotation. We measured neurovascular activity with fast event-related fMRI, distinguishing responses parametrically related to motor imagery from responses evoked by visual imagery and other task-related phenomena. By quantifying behavioral and neurovascular correlates of imagery on a trial-by-trial basis, we could discriminate between stimulus-related, mental rotation-related, and response-related neural activity. We found that specific portions of the posterior parietal and precentral cortex increased their activity as a function of mental rotation only during the motor imagery task. Within these regions, the parietal cortex was visually responsive, whereas the dorsal precentral cortex was not. Response- but not rotation-related activity was found around the left central sulcus (putative primary motor cortex) during both imagery tasks. Our study provides novel evidence on the topography and content of movement representations in the human brain. During intended action, the posterior parietal cortex combines somatosensory and visuomotor information, whereas the dorsal premotor cortex generates the actual motor plan, and the primary motor cortex deals with movement execution. We discuss the relevance of these results in the context of current models of action planning.

Adult↗

PubMed2004

Neural correlates of the chronic fatigue syndrome--an fMRI study.

Chronic fatigue syndrome (CFS) is characterized by a debilitating fatigue of unknown aetiology. Patients who suffer from CFS report a variety of physical complaints as well as neuropsychological complaints. Therefore, it is conceivable that the CNS plays a role in the pathophysiology of CFS. The purpose of this study was to investigate neural correlates of CFS, and specifically whether there exists a linkage between disturbances in the motor system and CFS. We measured behavioural performance and cerebral activity using rapid event-related functional MRI in 16 CFS patients and 16 matched healthy controls while they were engaged in a motor imagery task and a control visual imagery task. CFS patients were considerably slower on performance of both tasks, but the increase in reaction time with increasing task load was similar between the groups. Both groups used largely overlapping neural resources. However, during the motor imagery task, CFS patients evoked stronger responses in visually related structures. Furthermore, there was a marked between-groups difference during erroneous performance. In both groups, dorsal anterior cingulate cortex was specifically activated during error trials. Conversely, ventral anterior cingulate cortex was active when healthy controls made an error, but remained inactive when CFS patients made an error. Our results support the notion that CFS may be associated with dysfunctional motor planning. Furthermore, the between-groups differences observed during erroneous performance point to motivational disturbances as a crucial component of CFS.

Adult↗

PubMed2004

Genetic load on amygdala hypofunction during sadness in nonaffected brothers of schizophrenia patients.

OBJECTIVE: In a previous study, the authors reported that patients with schizophrenia show subcortical-limbic hypoactivity during sadness. In this study, they capitalized on those findings in order to assess the genetic influence of negative mood experience in schizophrenia patients. Brain activity was measured during mood induction in patients with schizophrenia and their first-degree nonaffected relatives. METHOD: Functional magnetic resonance imaging was used to investigate 13 male patients with schizophrenia, their nonaffected brothers (N=13), and a group of 26 individually matched healthy subjects unrelated to the siblings during induction of sad and happy moods as well as during a cognitive control task. A regional analysis was applied to investigate a possible subcortical-limbic dysfunction in relatives. RESULTS: Mood induction was successful in all groups according to subjective ratings. During sadness induction, the patients and their nonaffected siblings demonstrated less activity in the amygdala compared with the healthy group of nonrelatives. Other regions of interest, such as the left orbitofrontal cortex, the left superior temporal cortex, and the left precuneus/posterior cingulate revealed significant group differences only between patients and nonrelated healthy subjects. During positive mood induction, no group differences could be found in the amygdala. CONCLUSIONS: Following induction of sad mood, both patients with schizophrenia and their nonaffected brothers displayed reduced brain activity in the amygdala. Such hypoactivity is likely to represent a genetic influence and indicates that efficient compensatory mechanisms capable of preventing the onset of the illness must exist in nonaffected relatives.

Adult↗

PubMed2002

Differential involvement of parietal and precentral regions in movement preparation and motor intention.

Flexible goal-oriented behavior relies on spatial coordinate transformations and motor control mechanisms, but also on the capability to take advantage of contextual information for steering the sensorimotor machinery. Although accurate performance of a sensorimotor task requires parietal and frontal regions, their differential contribution and functional relationship with other associative regions remains obscure. We have used event-related functional magnetic resonance imaging to measure human cerebral activity associated with motor cognitive processes in the context of delayed performance of an associative visuomotor task. Movement instruction (specified by visual cues) and motor performance (specified by an auditory cue) were separated by a variable delay period. By manipulating the predictive value of the instruction cue, we distinguished delay-related activity influenced by response probabilities (motor preparation and motor inhibition) from delay-related activity unaffected by the likelihood of providing a motor response (motor intention). We found delay-related activity distributed across a cerebral network involving not only frontal circuitry, but also extrastriate and mediotemporal regions. Areas showing motor intentions and preparatory responses were spatially intermingled. Posterior parietal cortex deviated from this pattern, showing delay-related activity regardless of movement probability, but no specific preparatory responses. These results suggest that posterior parietal cortex and dorsal precentral cortex play different strategic roles in handling associative visuomotor problems. While parietal regions cover a range of potential responses defined by the task setting, precentral regions focus on a likely movement. Temporo-prefrontal regions might incorporate contextual information in the visuomotor process by defining potential and probable responses on the basis of the task contingencies.

Acoustic Stimulation↗

PubMed2002

Multiple movement representations in the human brain: an event-related fMRI study.

Neurovascular correlates of response preparation have been investigated in human neuroimaging studies. However, conventional neuroimaging cannot distinguish, within the same trial, between areas involved in response selection and/or response execution and areas specifically involved in response preparation. The specific contribution of parietal and frontal areas to motor preparation has been explored in electrophysiological studies in monkey. However, the associative nature of sensorimotor tasks calls for the additional contributions of other cortical regions. In this article, we have investigated the functional anatomy of movement representations in the context of an associative visuomotor task with instructed delays. Neural correlates of movement representations have been assessed by isolating preparatory activity that is independent from the performance of an actual motor act, or from the presence of a response's target. Movement instruction (specified by visual cues) and motor performance (specified by an auditory cue) were separated by a variable delay period. We have used whole-brain event-related fMRI to measure human brain activity during the performance of such a task. We have focused our analysis on specific preparatory activity, defined as a sustained response over variable delay periods between a transient visual instruction cue and a brief motor response, temporally independent from the transient events. Behavioral and electrophysiological controls ensured that preparatory activity was not contaminated by overt motor responses or working memory processes. We report suggestive evidence for multiple movement representations in the human brain. Specific sustained activity in preparation for an action was found not only in parieto-frontal regions but also in extrastriate areas and in the posterior portion of the superior temporal sulcus. We suggest that goal-directed preparatory activity relies on both visuomotor and visuoperceptual areas. These findings point to a functional-anatomical basis for the integration of perceptual and executive processes.

Adult↗

PubMed2002

Changes of cortico-striatal effective connectivity during visuomotor learning.

It has been suggested that the cortico-striatal system might play a crucial role in learning behavioural plans of action. We have tested this hypothesis by studying the dynamics of functional coupling among the neural elements of cortico-striatal circuitry. Human cerebral activity was measured with functional magnetic resonance imaging (fMRI) during the learning of an associative visuomotor task. Structural equation modelling of regional fMRI time-series was used to characterize learning-related changes in effective connectivity. We report that learning to associate visual instructions with motor responses significantly altered cortico-striatal functional couplings. Specific learning-related increases of effective connectivity were found in temporo-striatal and fronto-striatal circuits. Connectivity among portions of the frontal cortex decreased as a function of learning. Temporo-frontal and parieto-frontal couplings were not altered during learning. We infer that novel visuomotor associations are established through the enhancement of specific cortico-striatal circuits, rather than through the alteration of direct temporo-frontal or parieto-frontal connectivity.

Cerebral Cortex↗

PubMed2001

Movement preparation and working memory: a behavioural dissociation.

We can cross temporal sensorimotor contingencies by remembering sensory events or by anticipating motor responses. Here we tested the hypothesis that sensory and motor representations can be accessed according to different temporal dynamics. We predicted that the manipulation of movement representations would lead to a performance independent from the length of a delay interposed between sensory instructions and behavioural responses. Conversely, we expected a delay-dependent performance whenever temporary storage of sensory information was necessary to solve the task. We have measured reaction times and error rate in subjects performing a delayed non-matching to sample task. Task contingencies rather than explicit instructions ensured that either sensory or motor representations were used to cross the delay period on each trial. We tested our hypothesis by manipulating the length of the delays between stimulus presentation and behavioural response. We found that carrying sensory material over temporal gaps affects performance as a non-linear function of time, whereas movement representations remain robust over a wide range of delays. This novel behavioural paradigm might prove effective in dissociating the neural bases of preparatory and mnestic processes in normal human subjects, as well as their disorders in neurological patients.

Adult↗