Activation of human presupplementary motor area in learning of sequential procedures: a functional MRI study

Reduced size of the pre-supplementary motor cortex and impaired motor sequence learning in first-episode schizophrenia

Increasing evidence suggests that schizophrenia is associated with various morphological and functional abnormalities of the frontal cortex. So far research has concentrated on the dorsolateral and orbitofrontal cortex. Behavioral evidence suggests however that regions responsible for higher motor control are compromised in schizophrenia as well. The current study assessed volumes of the anterior supplementary motor area (pre-SMA) and implicit motor sequence learning in 15 subjects with first-episode schizophrenia and 15 healthy matched controls. Pre-SMA volumes were assessed by three-dimensional structural magnetic resonance imaging (3D-MRI) and manual parcellation according to an established protocol. Implicit motor sequence learning was assessed using the Serial Reaction-Time Task (SRTT). Compared with control subjects, schizophrenia subjects had significantly smaller volumes of the left pre-SMA (16%). Subjects with schizophrenia were severely impaired on sequence-specific implicit motor learning. Size of the left pre-SMA of schizophrenia subjects was significantly related to impaired implicit learning. We conclude that subjects with first-episode schizophrenia have a morphological abnormality of the left pre-SMA that might predispose them to develop disturbances of higher motor control during acute episodes of psychosis. These structural and behavioral abnormalities might be conceptualized within a broader model that views schizophrenia as a disorder of disturbed coordination of thought and action.

Motor learning in man: A review of functional and clinical studies

This chapter reviews results of clinical and functional imaging studies which investigated the time-course of cortical and subcortical activation during the acquisition of motor a skill. During the early phases of learning by trial and error, activation in prefrontal areas, especially in the dorsolateral prefrontal cortex, is has been reported. The role of these areas is presumably related to explicit working memory and the establishment of a novel association between visual cues and motor commands. Furthermore, motor associated areas of the right hemisphere and distributed cerebellar areas reveal strong activation during the early motor learning. Activation in superior-posterior parietal cortex presumably arises from visuospatial processes, while sensory feedback is coded in the anterior-inferior parietal cortex and the neocerebellar structures. With practice, motor associated areas of the left-hemisphere reveal increased activity. This shift to the left hemisphere has been observed regardless of the hand used during training, indicating a left-hemispheric dominance in the storage of visuomotor skills. Concerning frontal areas, learned actions of sequential character are represented in the caudal part of the supplementary motor area (SMA proper), whereas the lateral premotor cortex appears to be responsible for the coding of the association between visuo-spatial information and motor commands. Functional imaging studies which investigated the activation patterns of motor learning under implicit conditions identified for the first, a motor circuit which includes lateral premotor cortex and SMA proper of the left hemisphere and primary motor cortex, for the second, a cognitive loop which consists of basal ganglia structures of the right hemisphere. Finally, activity patterns of intermanual transfer are discussed. After right-handed training, activity in motor associated areas maintains during performance of the mirror version, but is increased during the performance of the original-oriented version with the left hand. In contrary, increased activity during the mirror reversed action, but not during the original-oriented performance of the untrained right hand is observed after left-handed training. These results indicate the transfer of acquired right-handed information which reflects the mirror symmetry of the body, whereas spatial information is mainly transferred after left-handed training. Taken together, a combined approach of clinical lesion studies and functional imaging is a promising tool for identifying the cerebral regions involved in the process of motor learning and provides insight into the mechanisms underlying the generalisation of actions.

Effects of explicit knowledge of workspace rotation in visuomotor sequence learning

Previous experimental and theoretical studies have suggested that two separate neural networks contribute to visuomotor learning of spatial sequences, one to the accuracy of performance and the other to the speed of performance (Nakahara et al. in J Cogn Neurosci 13:626-647, 2001). This study examined the influence of explicit knowledge of stimulus configuration (workspace) in visuomotor sequence learning. Twenty-eight right-handed subjects learned the sequences of button presses by trial and error (Hikosaka et al. in J Neurophysiol 76:617-621, 1996) in the course of two sessions. In the first session, both the number of completion failures (accuracy measure) and the performance time to complete a sequence (speed measure) decreased. In the second session, the workspace was rotated without notifying the subjects. About half the subjects remained unaware of the workspace rotation, and no transfer of learning occurred (i.e., neither accuracy nor speed of performance was preserved in the second session). The remaining subjects spontaneously noticed the rotation and they were able to use this knowledge to perform the task with less completion failures in the second session. However, the knowledge of workspace rotation did not decrease the performance time in the second session. The lack of influence of explicit knowledge on the speed of performance is consistent with the two-loop model of visuomotor sequence learning (Nakahara et al. in J Cogn Neurosci 13:626-647, 2001).

A consistent relationship between local white matter architecture and functional specialisation in medial frontal cortex

Functionally significant landmarks in the brain do not necessarily align with local sulcal and gyral architecture in a manner that is consistent across individuals. However, the functional specialisation underlying these landmarks is strongly constrained by the connectional architecture of the region. Here, we explore this relationship in the supplementary motor area (SMA) and pre-SMA in the medial frontal cortex of the human brain. Using diffusion tensor, conventional and functional MR imaging, we find that the location of the functional boundary between SMA and preSMA is more consistent with respect to specific features of the local white matter as it approaches neocortex than with respect to the local gyral and sulcal anatomy in the region.

The role of the supplementary motor area (SMA) in word production

The supplementary motor area (SMA) is a key structure for behavioral planning and execution. Recent research on motor control conducted with monkeys and humans has put to light an anatomical and functional distinction between pre-SMA and SMA-proper. According to this view, the pre-SMA would be involved in higher level processes while the SMA-proper would be more closely tied to motor output. We extended this general framework to the verbal domain, in order to investigate the role of the SMA in speech production. We conducted two speech production experiments with fMRI where we manipulated parameters such as familiarity, complexity or constraints on word selection. The results reveal a parcellation of the SMA into three distinct regions, according to their involvement in different aspects of word production. More specifically, following a rostrocaudal gradient, we observed differential activations related to lexical selection, linear sequence encoding and control of motor output. A parallel organization was observed in the dorsolateral frontal cortex. By refining its anatomical and functional parcellation, these results clarify the roles of the SMA in speech production.

MRI and fMRI analysis of oculomotor function

This chapter reviews the anatomical correlations of the cortical oculomotor centers in humans. The modern structural methods allow a better anatomical definition of the parietal, frontal and temporal structures involved in oculomotor control. Functional imaging reveals the cortical networks involved in saccadic, pursuit, and vestibular eye movements. Finally, the interaction of the network between attention and eye movements is discussed.

Functional interactions between oculomotor regions during prosaccades and antisaccades

Human behavior reflects a continual negotiation of automatic and directed actions. The oculomotor network is a well-characterized neural system in which to study this balance of behavioral control. For instance, saccades made toward and away from a flashed visual stimulus (prosaccades and antisaccades, respectively) are known to engage different cognitive processes. Brain regions important for such controlled execution include the presupplementary motor area (pre-SMA), frontal eye fields (FEF), and intraparietal sulcus (IPS). Recent work has emphasized various elements of this network but has not explored the functional interactions among regions. We used event-related fMRI to image human brain activity during performance of an interleaved pro/antisaccade task. Since traditional univariate statistics cannot address issues of functional connectivity, a multivariate technique is necessary. Coherence between fMRI time series of the pre-SMA with the FEF and IPS was used to measure functional interactions. The FEF, but not IPS, showed significant differential coherence between pro- and antisaccade trials with pre-SMA. These results suggest that the pre-SMA coordinates with FEF to maintain a controlled, preparatory set for task-appropriate oculomotor execution.

Reading fluent speech from talking faces: typical brain networks and individual differences

Listeners are able to extract important linguistic information by viewing the talker's face-a process known as ''speechreading.'' Previous studies of speechreading present small closed sets of simple words and their results indicate that visual speech processing engages a wide network of brain regions in the temporal, frontal, and parietal lobes that are likely to underlie multiple stages of the receptive language system. The present study further explored this network in a large group of subjects by presenting naturally spoken sentences which tap the richer complexities of visual speech processing. Four different baselines (blank screen, static face, nonlinguistic facial gurning, and auditory speech) enabled us to determine the hierarchy of neural processing involved in speechreading and to test the claim that visual input reliably accesses sound-based representations in the auditory cortex. In contrast to passively viewing a blank screen, the static-face condition evoked activation bilaterally across the border of the fusiform gyrus and cerebellum, and in the medial superior frontal gyrus and left precentral gyrus (p < .05, whole brain corrected). With the static face as baseline, the gurning face evoked bilateral activation in the motion-sensitive region of the occipital cortex, whereas visual speech additionally engaged the middle temporal gyrus, inferior and middle frontal gyri, and the inferior parietal lobe, particularly in the left hemisphere. These latter regions are implicated in lexical stages of spoken language processing. Although auditory speech generated extensive bilateral activation across both superior and middle temporal gyri, the group-averaged pattern of speechreading activation failed to include any auditory regions along the superior temporal gyrus, suggesting that f luent visual speech does not always involve sound-based coding of the visual input. An important finding from the individual subject analyses was that activation in the superior temporal gyrus did reach significance (p < .001, small-volume corrected) for a subset of the group. Moreover, the extent of the left-sided superior temporal gyrus activity was strongly correlated with speechreading performance. Skilled speechreading was also associated with activations and deactivations in other brain regions, suggesting that individual differences ref lect the efficiency of a circuit linking sensory, perceptual, memory, cognitive, and linguistic processes rather than the operation of a single component process.

Learning and production of movement sequences: behavioral, neurophysiological, and modeling perspectives

A wave of recent behavioral studies has generated a new wealth of parametric observations about serial order behavior. What was a trickle of neurophysiological studies has grown to a steady stream of probes of neural sites and mechanisms underlying sequential behavior. Moreover, simulation models of serial behavior generation have begun to open a channel to link cellular dynamics with cognitive and behavioral dynamics. Here we review major results from prominent sequence learning and performance tasks, namely immediate serial recall, typing, 2 x N, discrete sequence production, and serial reaction time. These tasks populate a continuum from higher to lower degrees of internal control of sequential organization and probe important contemporary issues such as the nature of working-memory representations for sequential behavior, and the development and role of chunks in hierarchical control. The main movement classes reviewed are speech and keypressing, both involving small amplitude movements amenable to parametric study. A synopsis of serial order models, vis-a-vis major empirical findings leads to a focus on competitive queuing (CQ) models. Recently, the many behavioral predictive successes of CQ models have been complemented by successful prediction of distinctively patterned electrophysiological recordings. In lateral prefrontal cortex, parallel activation dynamics of multiple neural ensembles strikingly matches the parallel dynamics predicted by CQ theory. An extended CQ simulation model--the N-STREAMS neural network model--exemplifies ongoing attempts to accommodate a broad range of both behavioral and neurobiological data within a CQ-consistent theory.

Context-dependent stimulation effects on saccade initiation in the presupplementary motor area of the monkey

Although evidence suggests that the contribution of the presupplementary motor area (pre-SMA) to voluntary motor control is effector-nonselective, the question of how electrical stimulation of the pre-SMA affects eye movements remains unanswered. To address this issue, stimulus effects of the pre-SMA of monkeys on saccade initiation were investigated during performance of a visually guided saccade task with an instructed delay period. This report describes two major findings. First, when stimuli with currents of < or =80 microA were applied before the presentation of a go signal, the reaction time (RT) of an upcoming saccade shortened with comparable effects on ipsi- and contraversive saccades. Second, stimuli that were delivered after the go signal lengthened the RT; this resulted in greater effects on ipsiversive saccades. In addition, the stimulation yielded a mild impairment of saccade accuracy, particularly when the stimulation was delivered after the go signal. By themselves, however, these stimuli did not directly elicit eye movements. Therefore the stimulus effects appeared only in the context of the behavioral task and were dependent on the phase of the task. These findings provide additional support for the hypothesis that the involvement of the pre-SMA in motor control can be linked to either eye or arm motor system dependent on behavioral context.

Increased corticospinal excitability after 5 Hz rTMS over the human supplementary motor area

Transcranial magnetic stimulation (TMS) can produce effects not only at the site of stimulation but also at distant sites to which it projects. Here we examined the connection between supplementary motor area (SMA) and the hand area of the primary motor cortex (M1(Hand)) by testing whether prolonged repetitive TMS (rTMS) over the SMA can produce changes in excitability of the M1(Hand) after the end of the stimulus train. We evaluated motor-evoked potentials (MEPs) and the cortical silent period (CSP) evoked by a single-pulse TMS, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) produced by a paired-pulse TMS, and forearm flexor H reflexes before and after 750 pulses of 5 Hz rTMS over SMA at an intensity of 110% active motor threshold (AMT) for the first dorsal interosseous (FDI) muscle. The amplitude of MEPs recorded from the right FDI muscle at rest as well as during voluntary contraction increased for at least 10 min after the end of rTMS, although the duration of the CSP, SICI and ICF did not change. There was no effect on H reflexes in the flexor carpi radialis muscle, even though the amplitude of the MEP obtained from the same muscle increased after rTMS. The effects on MEPs depended on the intensity of rTMS and were spatially specific to the SMA proper. We suggest that 5 Hz rTMS over SMA can induce a short-lasting facilitation in excitability of the M1(Hand) compatible with the anatomical connections between SMA and the M1(Hand).

Differential Roles of Neuronal Activity in the Supplementary and Presupplementary Motor Areas: From Information Retrieval to Motor Planning and Execution

We explored functional differences between the supplementary and presupplementary motor areas (SMA and pre-SMA, respectively) systematically with respect to multiple behavioral factors, ranging from the retrieval and processing of associative visual signals to the planning and execution of target-reaching movement. We analyzed neuronal activity while monkeys performed a behavioral task in which two visual instruction cues were given successively with a delay: one cue instructed the location of the reach target, and the other instructed arm use (right or left). After a second delay, the monkey received a motor-set cue to be prepared to make the reaching movement as instructed. Finally, after a GO signal, it reached for the instructed target with the instructed arm. We found the following apparent differences in activity: 1) neuronal activity preceding the appearance of visual cues was more frequent in the pre-SMA; 2) a majority of pre-SMA neurons, but many fewer SMA neurons, responded to the first or second cue, reflecting what was shown or instructed; 3) in addition, pre-SMA neurons often reflected information combining the instructions in the first and second cues; 4) during the motor-set period, pre-SMA neurons preferentially reflected the location of the target, while SMA neurons mainly reflected which arm to use; and 5) when executing the movement, a majority of SMA neurons increased their activity and were largely selective for the use of either the ipsilateral or contralateral arm. In contrast, the activity of pre-SMA neurons tended to be suppressed. These findings point to the functional specialization of the two areas, with respect to receiving associative cues, information processing, motor behavior planning, and movement execution.

Role of the cerebellum in implicit motor skill learning: a PET study

To depict neural substrates of implicit motor learning, regional cerebral blood flow was measured using positron emission tomography (PET) in 13 volunteers in the rest condition and during performance of a unimanual two-ball rotation task. Subjects rotated two balls in a single hand; a slow rotation (0.5 Hz) was followed by two sessions requiring as rapid rotation as possible. The process was repeated four times by a single hand (Block 1) and then by the opposite hand (Block 2). One group of volunteers began with the right hand (n = 7), and the other with the left (n = 6). Performance was assessed by both quickness and efficiency of movements. The former was assessed with the maximum number of rotation per unit time, and the latter with the electromyographic activity under constant speed of the movement. Both showed learning transfer from the right hand to the left hand. Activation of cerebrum and cerebellum varied according to hand. Activation common to both hands occurred in the bilateral dorsal premotor cortex and parasagittal cerebellum, right inferior frontal gyms, left lateral cerebellum and thalamus, supplementary motor area, and cerebellar vermis. The left lateral cerebellum showed the most prominent activation on the first trial of the novel task, and hence may be related the early phase of learning, or "what to do" learning. Left parasagittal cerebellum activity diminished with training both in first and second blocks, correlating inversely with task performance. This region may therefore be involved in later learning or "how to do" learning. The activity of these regions was less prominent with prior training than without it. Thus the left cerebellar hemisphere may be related to learning transfer across hands.

Selective activation and deactivation of the human brain structures between speeded and precisely timed tapping responses to identical visual stimulus: an fMRI study

We investigated the difference between brain activities in speeded and precisely timed responses to identical visual stimulus using fMRI. Stimulus used was a row of seven light-emitting diodes (LEDs) lightened up one after another with constant speed within a trial but with various speeds between trials. Subjects were asked to execute finger-thumb tapping with the right hand in response to the onset of the first LED light in the reaction time (RT) task and in anticipation of the onset of the last (i.e., seventh) LED light in the timing task. In control condition, they were asked to passively view the stimulus without motor response. Results showed that various movement-related areas including contralateral cingulate motor cortex were commonly activated for both tasks relative to the control condition, suggesting these structures are involved in general perception and response execution rather than specific function for speeded or precisely timed responses. In the RT task, the presupplementary motor area extending to the cingulate sulcus was activated more strongly than in the timing task probably to focus attention to the onset of the first LED light unpredictably presented after random foreperiods. The lateral occipital area extending to the temporo-parieto-occipital junction was activated more strongly in the timing task than in the RT task; the same area was deactivated in the RT task relative to the control condition. Auditory-related areas were also deactivated in the both tasks. This inter- and intramodal task-specific modification including deactivation underscores significance of the context for perception and action and can have an important role in dexterous or skilled performance.

Contributions of memory circuits to language: the declarative/procedural model

The structure of the brain and the nature of evolution suggest that, despite its uniqueness, language likely depends on brain systems that also subserve other functions. The declarative/procedural (DP) model claims that the mental lexicon of memorized word-specific knowledge depends on the largely temporal-lobe substrates of declarative memory, which underlies the storage and use of knowledge of facts and events. The mental grammar, which subserves the rule-governed combination of lexical items into complex representations, depends on a distinct neural system. This system, which is composed of a network of specific frontal, basal-ganglia, parietal and cerebellar structures, underlies procedural memory, which supports the learning and execution of motor and cognitive skills, especially those involving sequences. The functions of the two brain systems, together with their anatomical, physiological and biochemical substrates, lead to specific claims and predictions regarding their roles in language. These predictions are compared with those of other neurocognitive models of language. Empirical evidence is presented from neuroimaging studies of normal language processing, and from developmental and adult-onset disorders. It is argued that this evidence supports the DP model. It is additionally proposed that "language" disorders, such as specific language impairment and non-fluent and fluent aphasia, may be profitably viewed as impairments primarily affecting one or the other brain system. Overall, the data suggest a new neurocognitive framework for the study of lexicon and grammar.

Changes in brain activation during the acquisition of a new bimanual coodination task

Motor skill acquisition is associated with the development of automaticity and induces neuroplastic changes in the brain. Using functional magnetic resonance imaging (fMRI), the present study traced learning-related activation changes during the acquisition of a new complex bimanual skill, requiring a difficult spatio-temporal relationship between the limbs, i.e., cyclical flexion-extension movements of both hands with a phase offset of 90 degrees. Subjects were scanned during initial learning and after the coordination pattern was established. Kinematics of the movements were accurately registered and showed that the new skill was acquired well. Learning-related decreases in activation were found in right dorsolateral prefrontal cortex (DLPFC), right premotor, bilateral superior parietal cortex, and left cerebellar lobule VI. Conversely, learning-related increases in activation were observed in bilateral primary motor cortex, bilateral superior temporal gyrus, bilateral cingulate motor cortex (CMC), left premotor cortex, cerebellar dentate nuclei/lobule III/IV/Crus I, putamen/globus pallidus and thalamus. Accordingly, bimanual skill learning was associated with a shift in activation among cortico-subcortical regions, providing further evidence for the existence of differential cortico-subcortical circuits preferentially involved during the early and advanced stages of learning. The observed activation changes account for the transition from highly attention-demanding task performance, involving processing of sensory information and corrective action planning, to automatic performance based on memory representations and forward control.

How Self-Initiated Memorized Movements Become Automatic: A Functional MRI Study

We used functional magnetic resonance imaging (fMRI) and dual tasks to investigate the physiology of how movements become automatic. Normal subjects were asked to practice some self-initiated, self-paced, memorized sequential finger movements with different complexity until they could perform the tasks automatically. Automaticity was evaluated by having subjects perform a secondary task simultaneously with the sequential movements. Our secondary task was a letter-counting task where subjects were asked to identify the number of times a target letter from the letter sequences was seen. Only the performances that achieved high accuracy in both single and dual tasks were considered automatic. The fMRI results before and after automaticity was achieved were compared. Our data showed that for both conditions, sequential movements activated similar brain regions. No additional activity was observed in the automatic condition. There was less activity in bilateral cerebellum, presupplementary motor area, cingulate cortex, left caudate nucleus, premotor cortex, parietal cortex, and prefrontal cortex during the automatic stage. These findings suggest that most of the motor network participates in executing automatic movements and that it becomes more efficient as movements become more automatic. Our results do not provide evidence for any area to become more activated for automatic movements.

Participation of the primate presupplementary motor area in sequencing multiple saccades

The aim of this study was to investigate whether, and how, the presupplementary motor area (pre-SMA) is involved in the organization of oculomotor sequence. We trained two monkeys to perform three center-out saccades in six different orders. Each sequence consisted of a block of eight trials, initially with visual instruction (4 trials) and then from memory (4 trials). During memory-guided performance of sequential saccades, approximately 75% of task-related neuronal activity was selective for, or influenced by, the numerical position of saccades within each sequence (rank order). Neurons tuned for the direction of saccades were in the minority. We also found that 22% of sampled neurons increased their activity preferentially at a transitional period when monkeys were in the process of renewal of required saccade sequences. These data indicate that the pre-SMA is involved in the organization of oculomotor sequence, particularly in representing rank-order information and in updating sequence information. Together with previous reports on the participation of the pre-SMA in sequencing of multiple arm movements, we propose here that this area may contribute to cognitive aspects of sequential behavioral control, in an effector-independent manner.

Contrôle du mouvement du regard (2)

Saccades are very rapid eye movements allowing us to explore the visual world. Although most of the time unconscious, the programming of each saccade implies a complex decision which depends upon both the perceptual context and the intentions of the subject. The cerebral cortex is critically involved in deciding where, when and in which sequence we move the eyes. Using sophisticated experimental designs, such as the learning of sequences of saccades, has revealed that besides a core fronto-parietal circuit, prefrontal, cingulate, and mediotemporal regions seem critically involved in higher level oculomotor control. Understanding precisely the cortical networks associated to different components of ocular movements can certainly be very useful to characterize, test, and eventually detect various kinds of neurological pathology.

Motor Areas Beyond Motor Performance: Deficits in Serial Prediction Following Ventrolateral Premotor Lesions

Previous functional MRI findings have indicated that a premotor-parietal network is involved in the perceptual processing of sequential information. Given that premotor functions have traditionally been restricted to behaviors requiring motor or sensorimotor computations, the goal of the present patient study was to further investigate whether the lateral premotor cortex is critical in purely perceptual sequencing. Patients with either ventral premotor or inferior parietal lesions, in addition to patients with prefrontal lesions and age- and gender-matched healthy controls, were tested during the processing of temporal, object-specific, and spatial sequences. Results revealed that premotor patients as well as parietal patients showed significantly higher error rates than did healthy controls on all sequence tasks. In contrast, prefrontal patients showed no behavioral deficits. These findings support the significance of the ventrolateral premotor cortex, in addition to parietal areas, in nonmotor (attentional) functions.

Possible mechanism for transfer of motor skill learning: implication of the cerebellum

Transfer of learning takes place whenever our previous knowledge and skills affect the way in which new knowledge and skills are learned. The magnitude of transfer may depend on how prior memory is retrieved so that it may be relevant and usable in the present in terms of internal representation. This review highlights the power of neuroimaging techniques such as positron emission tomography (PET) to identify the underlying neuronal system of intermanual transfer by showing the asymmetry in the system for the same motor skill between hands. The review focuses on cerebellar cross-activation, cerebellar activation contralateral to the active hand, which would contribute to intermanual transfer of monkey tool-use learning, together with the fronto-parietal cortical circuit. Finally, this article proposes the relationship between the cerebellum and the possible mechanism underlying non-specific transfer that allows thinking in a flexible and productive manner.

Neuronal activity in motor cortical areas reflects the sequential context of movement

Natural actions can be described as chains of simple elements, whereas individual motion elements are readily concatenated to generate countless movement sequences. Sequence-specific neurons have been described extensively, suggesting that the motor system may implement temporally complex motions by using such neurons to recruit lower-level movement neurons modularly. Here, we set out to investigate whether activity of movement-related neurons is independent of the sequential context of the motion. Two monkeys were trained to perform linear arm movements either individually or as components of double-segment motions. However, comparison of neuronal activity between these conditions is delicate because subtle kinematic variations generally occur within different contexts. We therefore used extensive procedures to identify the contribution of variations in motor execution to differences in neuronal activity. Yet, even after application of these procedures we find that neuronal activity in the motor cortex (PMd and M1) associated with a given motion segment differs between the two contexts. These differences appear during preparation and become even more prominent during motion execution. Interestingly, despite context-related differences on the single-neuron level, the population as a whole still allows a reliable readout of movement direction regardless of the sequential context. Thus the direction of a movement and the sequential context in which it is embedded may be simultaneously and reliably encoded by neurons in the motor cortex.

Contrasting neuronal activity in the supplementary and frontal eye fields during temporal organization of multiple saccades

The organization of a series of actions into an appropriate temporal order is of particular importance in the voluntary control of motor behavior. Previous reports have emphasized the importance of medial motor areas for the temporal organization of movements. The aim of this study was to compare the neuronal activity in the supplementary and frontal eye fields (SEF and FEF) during sequential performance of multiple saccades to clarify the role of the two cortical oculomotor areas in the temporal organization of saccades based on memorized information. We analyzed neuronal activity while monkeys performed three saccades to peripheral targets in orders that were instructed and memorized. We found that activity that reflected saccade sequence or the numerical position of a saccade within a sequence (rank) was more prevalent in the SEF, whereas activity reflecting saccade direction was more dominant in the FEF. Furthermore, a sizeable number of SEF neurons exhibited an increase in activity when the animals were required to discard a current sequence and compose a novel sequence. We propose that the SEF is primarily involved in the process of planning, decoding, and updating saccade sequences, whereas the FEF plays a major role in determining the direction of forthcoming saccades.

Organization of action sequences and the role of the pre-SMA

To understand the contribution of the human presupplementary motor area (pre-SMA) in sequential motor behavior, we performed a series of finger key-press experiments. Experiment 1 revealed that each subject had a spontaneous tendency to organize or "chunk" a long sequence into shorter components. We hypothesized that the pre-SMA might have a special role in initiating each chunk but not at other points during the sequence. Experiment 2 therefore examined the effect of 0.5-s, 10-Hz repetitive transcranial magnetic stimulation (rTMS) directed over the pre-SMA. As hypothesized, performance was disrupted when rTMS was delivered over the pre-SMA at the beginning of the second chunk but not when it was delivered in the middle of a chunk. Contrary to the hypothesis, TMS did not disrupt sequence initiation. Experiments 3 and 4 examined whether the very first movement of a sequence could be disrupted under any circumstances. Pre-SMA TMS did disrupt the initiation of sequences but only when subjects had to switch between sequences and when the first movement of each sequence was not covertly instructed by a learned visuomotor association. In conjunction, the results suggest that for overlearned sequences the pre-SMA is primarily concerned with the initiation of a sequence or sequence chunk and the role of the pre-SMA in sequence initiation is only discerned when subjects must retrieve the sequence from memory as a superordinate set of movements without the aid of a visuomotor association. Control experiments revealed such effects were not present when rTMS was applied over the left dorsal premotor cortex.

Cortical control of ocular saccades in humans: a model for motricity

Our knowledge of the cortical control of saccadic eye movements (saccades) in humans has recently progressed mainly thanks to lesion and transcranial magnetic stimulation (TMS) studies, but also to functional imaging. It is now well-known that the frontal eye field is involved in the triggering of intentional saccades, the parietal eye field in that of reflexive saccades, the supplementary eye field (SEF) in the initiation of motor programs comprising saccades, the pre-SEF in learning of these programs, and the dorsolateral prefrontal cortex (DLPFC) in saccade inhibition, prediction and spatial working memory. Saccades may also be used as a convenient model of motricity to study general cognitive processes preparing movements, such as attention, spatial memory and motivation. Visuo-spatial attention appears to be controlled by a bilateral parieto-frontal network comprising different parts of the posterior parietal cortex and the frontal areas involved in saccade control, suggesting that visual attentional shifts and saccades are closely linked. Recently, our understanding of the cortical control of spatial memory has noticeably progressed by using the simple visuo-oculomotor model represented by the memory-guided saccade paradigm, in which a single saccade is made to the remembered position of a unique visual item presented a while before. TMS studies have determined that, after a brief stage of spatial integration in the posterior parietal cortex (inferior to 300 ms), short-term spatial memory (i.e. up to 15-20 s) is controlled by the DLPFC. Behavioral and lesion studies have shown that medium-term spatial memory (between 15-20 s and a few minutes) is specifically controlled by the parahippocampal cortex, before long-term memorization (i.e. after a few minutes) in the hippocampal formation. Lastly, it has been shown that the posterior part of the anterior cingulate cortex, called the cingulate eye field, is involved in motivation and the preparation of all intentional saccades, but not in reflexive saccades. These different but complementary study methods used in humans have thus contributed to a better understanding of both eye movement physiology and general cognitive processes preparing motricity as whole.

The functional anatomy of parkinsonian bradykinesia

To investigate the difficulty that patients with Parkinson's disease (PD) have in performing fast movements, we used H(2)(15)O PET to study regional cerebral blood flow (rCBF) associated with performance of a simple predictive visuomanual tracking task at three different velocities. Tracking movements in PD patients (versus tracking with the eyes alone) were associated with a general underactivation of the areas normally activated by the task (sensorimotor cortex contralateral to the moving arm, bilateral dorsal premotor cortices, and ipsilateral cerebellum). Presupplementary motor cortex (pre-SMA) ipsilateral to the moving arm had greater than normal movement-related activations. Increasing movement velocity led to increased rCBF in multiple premotor and parietal cortical areas and basal ganglia in the patients as opposed to the few cerebral locations that are normally velocity-related. The functional correlates of PD bradykinesia are: (1) impaired recruitment of cortical and subcortical systems that normally regulate kinematic parameters of movement such as velocity; and (2) increased recruitment of multiple premotor areas including both regions specialized for visuomotor control (ventral premotor and parietal cortices) and some that are not (pre-SMA). The overactivation of cortical regions observed in patients may be functional correlates of compensatory mechanisms and/or impaired suppression as a facet of the primary pathophysiology of PD.

Success and failure suppressing reflexive behavior

The dynamic interplay between reflexive and controlled determinants of behavior is one of the most general organizing principles of brain function. A powerful analogue of this interplay is seen in the antisaccade task, which pits reflexive and willed saccadic mechanisms against one another. Event-related functional magnetic resonance imaging of the human brain showed greater prestimulus preparatory activity in the pre-supplementary motor area before voluntary antisaccades (saccades away from a target) compared with reflexive prosaccades (saccades to a target). Moreover, this preparatory activity was critically associated with reflex suppression; it predicted whether the reflex was later successfully inhibited in the trial. These dataillustrate a mechanism for top-down control over reflexive behavior.

Rule learning in a serial reaction time task: an fMRI study on patients with early Parkinson's disease

In the present study, we investigated implicit rule learning in patients with Parkinson's disease (PD) and healthy participants. Functional magnetic resonance imaging (fMRI) and a variant of the serial reaction time task were employed to examine the performance of previously learned regular sequences. Participants responded to successively appearing visual stimuli by pressing spatially corresponding keys. Unbeknownst to them, a cycling 12-item sequence was presented. In order to measure rule learning independently from initial visuomotor learning, participants were trained with the sequence prior to scanning. In the fMRI session, alternating blocks of regular and random stimuli were performed. Imaging revealed activations in the frontomedian and posterior cingulate cortex during performance of sequence blocks as opposed to random blocks. The magnitude of activations in these two areas was correlated with the behavioral index for rule learning. As has been reported earlier, the frontomedian cortex may be involved in the prediction of future stimuli and anticipation of corresponding actions, whereas the posterior cingulate activation may rather be related to memory retrieval. Additional activations of the right putamen and the inferior frontal sulcus were not related to behavioral performance. In patients with early PD, the behavioral data showed reduced training effects during pretraining, but intact rule learning during the fMRI session. Imaging revealed highly similar frontomedian and posterior cingulate activations in patients and controls, in the absence of significant striatal and inferior frontal activations in patients. Our findings support the view that in early PD, with the lateral striatofrontal dopaminergic projections being affected, medial dopaminergic projections involved in the application of previously learned rules may still be spared.

Focused attention in a simple dichotic listening task: an fMRI experiment

Whole-head functional magnetic resonance imaging (fMRI) was used in nine neurologically intact subjects to measure the hemodynamic responses in the context of dichotic listening (DL). In order to eliminate the influence of verbal information processing, tones of different frequencies were used as stimuli. Three different dichotic listening tasks were used: the subjects were instructed to either concentrate on the stimuli presented in both ears (DIV), or only in the left (FL) or right (FR) ear and to monitor the auditory input for a specific target tone. When the target tone was detected, the subjects were required to indicate this by pressing a response button. Compared to the resting state, all dichotic listening tasks evoked strong hemodynamic responses within a distributed network comprising of temporal, parietal, and frontal brain areas. Thus, it is clear that dichotic listening makes use of various cognitive functions located within the dorsal and ventral stream of auditory information processing (i.e., the 'what' and 'where' streams). Comparing the three different dichotic listening conditions with each other only revealed a significant difference in the pre-SMA and within the left planum temporale area. The pre-SMA was generally more strongly activated during the DIV condition than during the FR and FL conditions. Within the planum temporale, the strongest activation was found during the FR condition and the weakest during the DIV condition. These findings were taken as evidence that even a simple dichotic listening task such as the one used here, makes use of a distributed neural network comprising of the dorsal and ventral stream of auditory information processing. In addition, these results support the previously made assumption that planum temporale activation is modulated by attentional strategies. Finally, the present findings uncovered that the pre-SMA, which is mostly thought to be involved in higher-order motor control processes, is also involved in cognitive processes operative during dichotic listening.

Disruption of information processing in the supplementary motor area of the MPTP-treated monkey: a clue to the pathophysiology of akinesia?

It has been suggested that the underactivity of mesial frontal structures induced by dopamine depletion could constitute one of the main substrates underlying akinesia in Parkinson's disease. Functional imaging and movement-related potential recordings indicate an implication of the frontal lobes in this pathological process, but the question has not yet been investigated at a cellular level using single unit recording. We therefore compared neuronal activity in both the presupplementary motor area (pre-SMA) and the supplementary motor area proper (SMAp) of the Macaca mulatta monkey during a delayed motor task, before and after MPTP treatment. In the pre-SMA, which receives strong inputs from the prefrontal cortex, the baseline firing frequency and the percentage of neurons responding to visual instruction cues decreased in lesioned monkeys. In the SMAp, which sends direct outputs to the primary motor cortex, not only was the response to visual cues impaired, but the percentage of SMAp neurons responding to intracortical microstimulation fell and the threshold of response rose. Neuronal activity after the Go signal diminished sharply in both structures in the symptomatic animal and the discharge pattern became more irregular; in the SMAp neuronal activity remained modified longer. Most of these changes could already be observed in the presymptomatic animal presenting no clinical signs of parkinsonism. These data would indicate that, at the moment when dopamine depletion has impaired the ability of cortical neurons to operate the focused selection of incoming information giving instructions for movement, pre-SMA and SMAp neurons are also in a state of severe hypoactivity. The conjunction of these phenomena could play a critical role in the genesis of akinesia.

A new approach to the functional systems of the brain

Action is the means by which animals survive. It consists of a complex combination of movements that are either innately endowed or acquired by learning. Innate and learned actions are controlled by different levels of neural networks: innate actions are controlled by reflex mechanisms and pattern generators in the spinal cord and brainstem, whereas learned actions are controlled by the cerebral cortex, basal ganglia, and cerebellum. However, these mechanisms are by no means independent. Recent studies have shown that multiple brain areas contribute to the implementation of learned actions. Based on a series of studies using a sequenced learning task with trial and error, we propose a hypothetical scheme in which a sequential procedure is acquired independently by two cortical systems, one using spatial coordinates, and the other using motor coordinates. They are active preferentially in the early and late stages of learning, respectively. Both of the systems are supported by loop circuits formed with the basal ganglia and the cerebellum, the former for reward-based evaluation and the latter for processing of timing. The proposed neural architecture would operate in a flexible manner to acquire and execute multiple sequential procedures.

Dynamic patterns make the premotor cortex interested in objects: influence of stimulus and task revealed by fMRI

Research in monkey and man indicates that the ventrolateral premotor cortex (PMv) underlies not only the preparation of manual movements, but also the perceptual representation of pragmatic object properties. However, visual stimuli without any pragmatic meaning were recently found to elicit selective PMv responses if they were subjected to a perceivable pattern of change. We used functional magnetic resonance imaging (fMRI) to investigate if perceptual representations in the PMv might apply not only to pragmatic, but also to dynamic stimulus properties. To this end, a sequential figure matching task that required the processing of dynamic features was contrasted with a non-figure control task (Experiment 1) and an individual figure matching task (Experiment 2). In order to control for potential influences of stimulus properties that might be associated with pragmatic attributes, different types of abstract visual stimuli were employed. The experiments yielded two major findings: if their dynamic properties are attended, then abstract 2D visual figures are sufficient to trigger activation within premotor areas involved in hand-object interaction. Moreover, these premotor activations are independent from stimulus properties that might relate to pragmatic features. The results imply that the PMv is engaged in the processing of stimuli that are usually or actually embedded within either a pragmatic or a dynamic context.

Premotor cortex is involved in restoration of gait in stroke

Cortical activation during hemiplegic gait was assessed in six nonambulatory patients with severe stroke (four men, two women; four with right and two with left hemiplegia; 57 years old and 3 months after stroke on average), using a near-infrared spectroscopic imaging system. Each patient performed tasks of treadmill walking (0.2km/hr), alternated with rest every 30 seconds for four repetitions, under partial body weight support, either with mechanical assistance in swinging the paretic leg control (CON) or with a facilitation technique that enhanced swinging of the paretic leg (FT), provided by physical therapists. Gait performance was associated with increased oxygenated hemoglobin levels in the medial primary sensorimotor cortex in the unaffected hemisphere greater than in the affected hemisphere. Both cortical mappings and quantitative data showed that the premotor activation in the affected hemisphere was enhanced during hemiplegic gait. There was also a prominent activation in the presupplementary motor area. Overall cortical activations and gait performance were greater in walking with FT than with CON. These indicate that multiple motor areas including the premotor cortex and presupplementary motor area might play important roles in restoration of gait in patients with severe stroke.

Bimanual coordination and interhemispheric interaction

Bimanual coordination of skilled finger movements requires intense functional coupling of the motor areas of both cerebral hemispheres. This coupling can be measured non-invasively in humans with task-related coherence analysis of multi-channel surface electroencephalography. Since bimanual coordination is a high-level capability that virtually always requires training, this review is focused on changes of interhemispheric coupling associated with different stages of bimanual learning. Evidence is provided that the interaction between hemispheres is of particular importance in the early phase of command integration during acquisition of a novel bimanual task. It is proposed that the dynamic changes in interhemispheric interaction reflect the establishment of efficient bimanual 'motor routines'. The effects of callosal damage on bimanual coordination and learning are reviewed as well as functional imaging studies related to bimanual movement. There is evidence for an extended cortical network involved in bimanual motor activities which comprises the bilateral primary sensorimotor cortex (SM1), supplementary motor area, cingulate motor area, dorsal premotor cortex and posterior parietal cortex. Current concepts about the functions of these structures in bimanual motor behavior are reviewed.

Role of the human medial frontal cortex in task switching: a combined fMRI and TMS study

We used event-related functional magnetic resonance imaging (fMRI) to measure brain activity when subjects were performing identical tasks in the context of either a task-set switch or a continuation of earlier performance. The context, i.e., switching or staying with the current task, influenced medial frontal cortical activation; the medial frontal cortex is transiently activated at the time that subjects switch from one way of performing a task to another. Two types of task-set-switching paradigms were investigated. In the response-switching (RS) paradigm, subjects switched between different rules for response selection and had to choose between competing responses. In the visual-switching (VS) paradigm, subjects switched between different rules for stimulus selection and had to choose between competing visual stimuli. The type of conflict, sensory (VS) or motor (RS), involved in switching was critical in determining medial frontal activation. Switching in the RS paradigm was associated with clear blood-oxygenation-level-dependent signal increases ("activations") in three medial frontal areas: the rostral cingulate zone, the caudal cingulate zone, and the presupplementary motor area (pre-SMA). Switching in the VS task was associated with definite activation in just one medial frontal area, a region on the border between the pre-SMA and the SMA. Subsequent to the fMRI session, we used MRI-guided frameless stereotaxic procedures and repetitive transcranial magnetic stimulation (rTMS) to test the importance of the medial frontal activations for task switching. Applying rTMS over the pre-SMA disrupted subsequent RS performance but only when it was applied in the context of a switch. This result shows, first, that the pre-SMA is essential for task switching and second that its essential role is transient and limited to just the time of behavioral switching. The results are consistent with a role for the pre-SMA in selecting between response sets at a superordinate level rather than in selecting individual responses. The effect of the rTMS was not simply due to the tactile and auditory artifacts associated with each pulse; rTMS over several control regions did not selectively disrupt switching. Applying rTMS over the SMA/pre-SMA area activated in the VS paradigm did not disrupt switching. This result, first, confirms the limited importance of the medial frontal cortex for sensory attentional switching. Second, the VS rTMS results suggest that just because an area is activated in two paradigms does not mean that it plays the same essential role in both cases.

Intermanual coordination: from behavioural principles to neural-network interactions

Locomotion in vertebrates and invertebrates has a long history in research as the most prominent example of interlimb coordination. However, the evolution towards upright stance and gait has paved the way for a bewildering variety of functions in which the upper limbs interact with each other in a context-specific manner. The neural basis of these bimanual interactions has been investigated in recent years on different scales, ranging from the single-cell level to the analysis of neuronal assemblies. Although the prevailing viewpoint has been to assign bimanual coordination to a single brain locus, more recent evidence points to a distributed network that governs the processes of neural synchronization and desynchronization that underlie the rich variety of coordinated functions. The distributed nature of this network accounts for disruptions of interlimb coordination across various movement disorders.

Long-term consequences of switching handedness: a positron emission tomography study on handwriting in "converted" left-handers

Until some decades ago, left-handed children who attended German schools were forced to learn to write with their right hand. To explore the long-term consequences of switching handedness, we studied the functional neuroanatomy of handwriting in 11 adult "converted" left-handers and 11 age-matched right-handers. All participants had used exclusively their right hand for writing since early childhood. Using [15O]H2O positron emission tomography, changes in normalized regional cerebral blood flow (rCBF) were assessed while participants repetitively wrote a stereotyped word with their right hand. The kinematics of handwriting did not differ between converted left-handers and right-handers. In innate right-handers, handwriting caused a preponderant left-hemispheric activation of parietal and premotor association areas. In contrast, converted left-handers demonstrated a more bilateral activation pattern with distinct activation foci in the right lateral premotor, parietal, and temporal cortex. Moreover, foci in the right rostral supplementary motor area and the right inferior parietal lobule demonstrated a positive linear relationship between the degree of "left-handedness" and normalized rCBF during right-hand writing. Functional activity in the primary sensorimotor cortex was not affected by handedness. Our findings provide evidence for persisting differences in the functional neuroanatomy of handwriting between right-handers and converted left-handers, despite decades of right-hand writing. Right-hemispheric activation in converted left-handers may reflect suppression of unwanted left-hand movements. Alternatively, this activity may represent persistent left-handedness and, as such, demonstrate a hemispheric asymmetry of hand movement representations in cortical motor association areas in relation to the direction and degree of handedness.

Comparison of neuronal activity in the rostral supplementary and cingulate motor areas during a task with cognitive and motor demands

A number of cortical motor areas have been identified on the medial wall of the hemisphere in monkeys. However, their specific role in motor control remains unclear. In this study, we sought to describe and compare the functional properties of the presupplementary (pre-SMA) and rostral cingulate (CMAr) motor areas in two monkeys performing a visually instructed, delayed, sequential movement. We recorded 134 task-related neurons in the pre-SMA and 149 in the CMAr. The main difference between the two areas was the abundance of responses to targets (46%) in the pre-SMA, while CMAr activity was more related to reward (28%). Neuronal responses to targets were more phasic and higher in frequency in the pre-SMA than in the CMAr. During the delay, the percentage of neuronal responses was similar in the two areas. The discharge pattern was different depending upon whether the delay duration was fixed or variable but in most neurons was the same regardless of the sequence performed. Movement-related changes were common in the pre-SMA (75%) and in the CMAr (81%) but they occurred earlier in the former. Neurons activated exclusively during movement were more numerous in the CMAr. Finally, neuronal activity in the pre-SMA was more related to the sequential aspect of the task compared to the CMAr. Our results suggest that although the two areas share functional properties, they also participate in different aspects of motor behaviour. Their functional properties reflect their anatomical positions, which give them the potential to integrate external stimuli (pre-SMA) and internal states (CMAr) during motor planning.

Imaging the premotor areas

Recent imaging studies of motor function provide new insights into the organization of the premotor areas of the frontal lobe. The pre-supplementary motor area and the rostral portion of the dorsal premotor cortex, the 'pre-PMd', are, in many respects, more like prefrontal areas than motor areas. Recent data also suggest the existence of separate functional divisions in the rostral cingulate zone.

Sequential learning in non-human primates

Sequential learning plays a role in a variety of common tasks, such as human language processing, animal communication, and the learning of action sequences. In this article, we investigate sequential learning in non-human primates from a comparative perspective, focusing on three areas: the learning of arbitrary, fixed sequences; statistical learning; and the learning of hierarchical structure. Although primates exhibit many similarities to humans in their performance on sequence learning tasks, there are also important differences. Crucially, non-human primates appear to be limited in their ability to learn and represent the hierarchical structure of sequences. We consider the evolutionary implications of these differences and suggest that limitations in sequential learning may help explain why non-human primates lack human-like language.

Organization of inputs from cingulate motor areas to basal ganglia in macaque monkey

The cingulate motor areas reside within regions lining the cingulate sulcus and are divided into rostral and caudal parts. Recent studies suggest that the rostral and caudal cingulate motor areas participate in distinct aspects of motor function: the former plays a role in higher-order cognitive control of movements, whereas the latter is more directly involved in their execution. Here, we investigated the organization of cingulate motor areas inputs to the basal ganglia in the macaque monkey. Identified forelimb representations of the rostral and caudal cingulate motor areas were injected with different anterograde tracers and the distribution patterns of labelled terminals were analysed in the striatum and the subthalamic nucleus. Corticostriatal inputs from the rostral and caudal cingulate motor areas were located within the rostral striatum, with the highest density in the striatal cell bridges and the ventrolateral portions of the putamen, respectively. There was no substantial overlap between these input zones. Similarly, a certain segregation of input zones from the rostral and caudal cingulate motor areas occurred along the mediolateral axis of the subthalamic nucleus. It has also been revealed that corticostriatal and corticosubthalamic input zones from the rostral cingulate motor area considerably overlapped those from the presupplementary motor area, while the input zones from the caudal cingulate motor area displayed a large overlap with those from the primary motor cortex. The present results indicate that a parallel design underlies motor information processing in the cortico-basal ganglia loop derived from the rostral and caudal cingulate motor areas.

Functional brain mapping of monkey tool use

When using a tool, we can perceive a psychological association between the tool and the body parts-the tool is incorporated into our "body-image." During tool use, visual response properties of bimodal (tactile and visual) neurons in the intraparietal area of the monkey's cerebral cortex were modified to include the hand-held tool. Visual properties of the monkey intraparietal neurons may represent the body-image in the brain. We explored tool use-induced activation within the intraparietal area and elsewhere in alert monkey brain using positron emission tomography (PET). Tool use-related activities compared with the control condition (simple-stick manipulation) revealed a significant increase in cerebral blood flow in the corresponding intraparietal region, basal ganglia, presupplementary motor area, premotor cortex, and cerebellum. These tool use-specific areas may participate in maintaining and updating the body-image for the precise guidance of a hand-held rake onto a distant reward.

Stimulus-response incompatibility activates cortex proximate to three eye fields

We used functional magnetic resonance imaging (fMRI) to investigate cortical activation during the performance of three oculomotor tasks that impose increasing levels of cognitive demand. (1) In a visually guided saccade (VGS) task, subjects made saccades to flashed targets. (2) In a compatible task, subjects made leftward and rightward saccades in response to foveal presentation of the uppercase words "LEFT" or "RIGHT." (3) In a mixed task, subjects made rightward saccades in response to the lowercase word "left" and leftward saccades in response to the lowercase word "right" on incompatible trials (60%). The remaining 40% of trials required compatible responses to uppercase words. The VGS and compatible tasks, when compared to fixation, activated the three cortical eye fields: the supplementary eye field (SEF), the frontal eye field (FEF), and the parietal eye field (PEF). The mixed task, when compared to the compatible task, activated three additional cortical regions proximate to the three eye fields: (1) rostral to the SEF in medial frontal cortex; (2) rostral to the FEF in dorsolateral prefrontal cortex (DLPFC); (3) rostral and lateral to the PEF in posterior parietal cortex. These areas may contribute to the suppression of prepotent responses and in holding novel visuomotor associations in working memory.

Hemispheric lateralization in the cortical motor preparation for human vocalization

To investigate the cortical information processing during the preparation of vocalization, we performed transcranial magnetic stimulation (TMS) over the cortex while the subjects prepared to produce voice in response to a visual cue. The control reaction time (RT) of vocalization without TMS was 250-350 msec. TMS prolonged RT when it was delivered up to 150-200 msec before the expected onset of voice (EOV). The largest delay of RT was induced bilaterally over points 6 cm to the left and right of the vertex (the left and right motor areas), resulting in 10-20% prolongation of RT. During the early phase of prevocalization period (50-100 msec before EOV), the delay induced over the left motor area was slightly larger than that induced over the right motor area, whereas, during the late phase (0-50 msec before EOV), it was significantly larger over the right motor area. Bilateral and simultaneous TMS of the left and right motor areas induced delays not significantly different from that induced by unilateral TMS during the early phase, but induced a large delay well in excess of the latter during the late phase. Thus, during the cortical preparation for human vocalization, alternation of hemispheric lateralization takes place between the bilateral motor cortices near the facial motor representations, with mild left hemispheric predominance at the early phase switching over to robust right hemispheric predominance during the late phase. Our results also suggested involvement of the motor representation of respiratory muscles and also of supplementary motor cortex.

Cerebellar projections to the prefrontal cortex of the primate

The cerebellum is known to project via the thalamus to multiple motor areas of the cerebral cortex. In this study, we examined the extent and anatomical organization of cerebellar input to multiple regions of prefrontal cortex. We first used conventional retrograde tracers to map the origin of thalamic projections to five prefrontal regions: medial area 9 (9m), lateral area 9 (9l), dorsal area 46 (46d), ventral area 46, and lateral area 12. Only areas 46d, 9m, and 9l received substantial input from thalamic regions included within the zone of termination of cerebellar efferents. This suggested that these cortical areas were the target of cerebellar output. We tested this possibility using retrograde transneuronal transport of the McIntyre-B strain of herpes simplex virus type 1 from areas of prefrontal cortex. Neurons labeled by retrograde transneuronal transport of virus were found in the dentate nucleus only after injections into areas 46d, 9m, and 9l. The precise location of labeled neurons in the dentate varied with the prefrontal area injected. In addition, the dentate neurons labeled after virus injections into prefrontal areas were located in regions spatially separate from those labeled after virus injections into motor areas of the cerebral cortex. Our observations indicate that the cerebellum influences several areas of prefrontal cortex via the thalamus. Furthermore, separate output channels exist in the dentate to influence motor and cognitive operations. These results provide an anatomical substrate for the cerebellum to be involved in cognitive functions such as planning, working memory, and rule-based learning.

Response Anticipation Processes in the Learning of a Sensorimotor Sequence

Abstract We investigated the contribution of motor processes to implicit and explicit serial learning by means of event-related brain potentials. An otherwise predictable sequence of S-R pairs was occasionally interrupted by stimuli that violated either the stimulus or the response sequence (perceptual or motor deviants). After performing the task, participants were asked to recall as much of the sequence as possible. On the basis of these free recall results, two groups of subjects (explicit and implicit learners) were formed. Reaction time was prolonged for motor deviants but not for perceptual deviants, which violated the predictable sequence of stimulus locations. Early activation in the lateralized readiness potential (LRP) for standard stimuli and an activation of the expected but incorrect response for deviants violating the response sequence indicate the contribution of motor processes to serial learning. ERPs did not show any learning-related changes. Furthermore, in all dependent measures no differences between explicit and implicit learners were observed. The results are at variance with previous claims that serial learning is a purely perceptual process.

Activation of frontoparietal cortices during memorized triple-step sequences of saccadic eye movements: an fMRI study

To determine the cortical areas controlling memory-guided sequences of saccadic eye movements, we performed functional magnetic resonance imaging (fMRI) in six healthy adults. Subjects had to perform a memorized sequence of three saccades in darkness, after a triple-step stimulus of successively flashed laser targets. To assess the differential contribution of saccadic subfunctions, we applied several control conditions, such as central fixation with or without triple-step visual stimulation, self-paced saccades in darkness, visually guided saccades and single memory-guided saccades. Triple-step saccades strongly activated the regions of the frontal eye fields, the adjacent ventral premotor cortex, the supplementary eye fields, the anterior cingulate cortex and several posterior parietal foci in the superior parietal lobule, the precuneus, and the middle and posterior portion of the intraparietal sulcus, the probable location of the human parietal eye field. Comparison with the control conditions showed that the right intraparietal sulcus and parts of the frontal and supplementary eye fields are more involved in the execution of triple-step saccades than in the other saccade tasks. In accordance with evidence from clinical lesion studies, we propose that the supplementary eye field essentially controls the triggering of memorized saccadic sequences, whereas activation near the middle portion of the right intraparietal sulcus appears to reflect the necessary spatial computations, including the use of extraretinal information (efference copy) about a saccadic eye displacement for updating the spatial representation of the second or third target of the triple-step sequence.