Motor Areas of the Medial Wall: A Review of Their Location and Functional Activation

Our goal in this review is to provide an anatomical frameworkfor the analysis of the motor functions of the medial wall ofthe hemisphere in humans and laboratory primates. Convergingevidence indicates that this region of the frontal lobe containsmultiple areas involved in motor control. In the monkey, themedial wall contains four premotor areas that project directlyto both the primary motor cortex and the spinal cord. Theseare the supplementary motor area (SMA) on the superior frontalgyrus and three motor areas buried within the cingulate sulcus.In addition, there is evidence that a fifth motor field. thepre-SMA. lies rostral to the SMA proper. Recent physiologicalobservations provide evidence for functional differences amongthese motor fields. In the human, no consensus exists on the number of distinctmotor fields on the medial wall. In this review, we summarizethe results of positron emission tomography (PET) studies thatexamined functional activation on the medial wall of humans.Our analysis suggests that it is possible to identify at leastfour separate cortical areas on the medial wall. Each area appearsto be relatively more involved in some aspects of motor behaviorthan others. These cortical areas in the human appear to beanalogous to the pre-SMA, the SMA proper, and two of the cingulatemotor areas of the monkey. We believe that these correspondencesand the anatomical framework we describe will be important forunraveling the motor functions of the medial wall of the hemisphere.     

Goal-selection and movement-related conflict during bimanual reaching movements

Conflict during bimanual movements can arise during the selection of movement goals or during movement planning and execution. We demonstrate a behavioral and neural dissociation of these 2 types of conflict. During functional magnetic resonance imaging scanning, participants performed bimanual reaching movements with symmetric (congruent) or orthogonal (incongruent) trajectories. The required movements were indicated either spatially, by illuminating the targets, or symbolically, using centrally presented letters. The processing of symbolic cues led to increased activation in a left hemisphere network including the intraparietal sulcus, premotor cortex, and inferior frontal gyrus. Reaction time cost for incongruent movements was substantially larger for symbolic than for spatial cues, indicating that the cost was primarily associated with the selection and assignment of movement goals, demands that are minimized when goals are directly specified by spatial cues. This goal-selection conflict increased activity in the pre-supplementary motor area and cingulate motor areas. Both cueing conditions led to larger activation for incongruent movements in the convexity of the superior parietal cortex, bilaterally, making this region a likely neural site for conflict that arises during the planning and execution of bimanual movements. These results suggest distinct neural loci for 2 forms of constraint on our ability to perform bimanual reaching movements.     

Early Decay of Pain-related Cerebral Activation in Functional Magnetic Resonance Imaging: Comparison with Visual and Motor Tasks

Background: Although pain-related activation was localized in multiple brain areas by functional imaging, the temporal profile of its signal has been poorly understood. The authors characterized the temporal evolution of such activation in comparison to that by conventional visual and motor tasks using functional magnetic resonance imaging.

Methods: Five right-handed volunteers underwent whole brain echo-planar imaging on a 3 T magnetic resonance imaging scanner while they received pain stimulus on the right and left forearm and performed visually guided saccade and finger tapping tasks. Pain stimulus on the right and left forearm consisted of four cycles of 15-s stimulus at 47.2-49.0[degrees]C, interleaved with 30-s control at 32[degrees]C, delivered by a Peltier-type thermode, and visually guided saccade and finger tapping of three cycles of 30-s active and 30-s rest conditions. Voxel-wise t statistical maps were standardized and averaged across subjects. Blood oxygenation level-dependent signal time courses were analyzed at local maxima of representative activation clusters (t > 3.5).

Results: Pain stimulus on the right forearm activated the secondary somatosensory (S2), superior temporal, anterior cingulate, insular, prefrontal cortices, premotor area, and lenticular nucleus. Pain stimulus on the left forearm activated similar but fewer areas at less signal intensity. The S2 activation was dominant on the contralateral hemisphere. Pain-related activation was statistically weaker and showed less consistent signal time courses than visually guided saccade- and finger tapping-related activation. Pain-related signals decayed earlier before the end of stimulus, in contrast to well-sustained signal plateaus induced by visually guided saccade and finger tapping.     

Early decay of pain-related cerebral activation in functional magnetic resonance imaging: comparison with visual and motor tasks.

BACKGROUND: Although pain-related activation was localized in multiple brain areas by functional imaging, the temporal profile of its signal has been poorly understood. The authors characterized the temporal evolution of such activation in comparison to that by conventional visual and motor tasks using functional magnetic resonance imaging. METHODS: Five right-handed volunteers underwent whole brain echo-planar imaging on a 3 T magnetic resonance imaging scanner while they received pain stimulus on the right and left forearm and performed visually guided saccade and finger tapping tasks. Pain stimulus on the right and left forearm consisted of four cycles of 15-s stimulus at 47.2-49.0 degrees C, interleaved with 30-s control at 32 degrees C, delivered by a Peltier-type thermode, and visually guided saccade and finger tapping of three cycles of 30-s active and 30-s rest conditions. Voxel-wise t statistical maps were standardized and averaged across subjects. Blood oxygenation level-dependent signal time courses were analyzed at local maxima of representative activation clusters (t > 3.5). RESULTS: Pain stimulus on the right forearm activated the secondary somatosensory (S2), superior temporal, anterior cingulate, insular, prefrontal cortices, premotor area, and lenticular nucleus. Pain stimulus on the left forearm activated similar but fewer areas at less signal intensity. The S2 activation was dominant on the contralateral hemisphere. Pain-related activation was statistically weaker and showed less consistent signal time courses than visually guided saccade- and finger tapping-related activation. Pain-related signals decayed earlier before the end of stimulus, in contrast to well-sustained signal plateaus induced by visually guided saccade and finger tapping. CONCLUSIONS: The authors speculate that pain-related blood oxygenation level-dependent signals were attenuated by the pain-induced global cerebral blood flow decrease or activation of the descending pain inhibitory systems.     

Functional Anatomy of Pointing and Grasping in Humans

The functional anatomy of reaching and grasping simple objectswas determined in nine healthy subjects with positron emissiontomography imaging of regional cerebral blood flow (rCBF). Ina prehension (grasping) task, subjects reached and grasped illuminatedcylindrical objects with their right hand. In a pointing task,subjects reached and pointed over the same targets. In a controlcondition subjects looked at the targets. Both movement tasksincreased activity in a distributed set of cortical and subcorticalsites: contralateral motor, premotor, ventral supplementarymotor area (SMA), cingulate, superior parietal, and dorsal occipitalcortex. Cortical areas including cuneate and dorsal occipitalcortex were more extensively activated than ventral occipitalor temporal pathways. The left parietal operculum (putativeSII) was recruited during grasping but not pointing. Blood flowchanges were individually localized with respect to local corticalanatomy using sulcal landmarks. Consistent anatomic landmarksfrom MRI scans could be identified to locate sensorimotor, ventralSMA, and SII blood flow increases. The time required to completeindividual movements and the amount of movement made duringimaging correlated positively with the magnitude of rCBF increasesduring grasping in the contralateral inferior sensorimotor,cingulate, and ipsilateral inferior temporal cortex, and bilateralanterior cerebellum. This functional-anatomic study definesa cortical system for "pragmatic" manipulation of simple neutralobjects.     

Watching your foot move--an fMRI study of visuomotor interactions during foot movement

The objective of this study was to investigate brain areas involved in distinguishing sensory events caused by self-generated movements from similar sensory events caused by externally generated movements using functional magnetic resonance imaging. Subjects performed 4 types of movements: 1) self-generated voluntary movement with visual feedback, 2) externally generated movement with visual feedback, 3) self-generated voluntary movement without visual feedback, and 4) externally generated movement without visual feedback, this design. This factorial design makes it possible to study which brain areas are activated during self-generated ankle movements guided by visual feedback as compared with externally generated movements under similar visual and proprioceptive conditions. We found a distinct network, comprising the posterior parietal cortex and lateral cerebellar hemispheres, which showed increased activation during visually guided self-generated ankle movements. Furthermore, we found differential activation in the cerebellum depending on the different main effects, that is, whether movements were self- or externally generated regardless of visual feedback, presence or absence of visual feedback, and activation related to proprioceptive input.     

Motor cortex dynamics in visuomotor production of speech and non-speech mouth movements

We investigated timing and hemispheric balance of motor cortex activation when kinetically similar speech and non-speech mouth movements and sequences of such movements were triggered by visually presented letter- and symbol-strings. As an index of motor cortex activation, we used magnetoencephalographic recording of task-related change of precentral 20 Hz (16-24 Hz) activity. Suppression of the 20 Hz rhythm revealed pre-movement activation in the face representation areas that was tied to visual instruction, not movement onset. The 20 Hz rhythm remained suppressed throughout the preparation and execution of mouth movements and was followed by post-movement rebound. Left hemisphere preceded the right at the onset and offset of the suppression, similarly for isolated and sequential speech and non-speech movements. Pattern of task-related change in 20 Hz activity was otherwise symmetrical. In the face areas, the overall modulation of 20 Hz activity increased with sequence length and motor demands. Hand representation areas showed also weak reactivity, with systematically larger modulation of 20 Hz activity for non-speech than speech movements. Our results suggest an active role for the motor cortex in cognitive control of visually triggered mouth movements, not limited to movement execution.     

Motor Mapping with Functional Magnetic Resonance Imaging: Comparison with Electrical Cortical Stimulation

The aim of the present study was to evaluate motor area mapping using functional magnetic resonance imaging (fMRI) compared with electrical cortical stimulation (ECS). Motor mapping with fMRI and ECS were retrospectively compared in seven patients with refractory epilepsy in which the primary motor (M1) areas were identified by fMRI and ECS mapping between 2012 and 2019. A right finger tapping task was used for fMRI motor mapping. Blood oxygen level-dependent activation was detected in the left precentral gyrus (PreCG)/postcentral gyrus (PostCG) along the “hand knob” of the central sulcus in all seven patients. Bilateral supplementary motor areas (SMAs) were also activated (n = 6), and the cerebellar hemisphere showed activation on the right side (n = 3) and bilateral side (n = 4). Furthermore, the premotor area (PM) and posterior parietal cortex (PPC) were also activated on the left side (n = 1) and bilateral sides (n = 2). The M1 and sensory area (S1) detected by ECS included fMRI-activated PreCG/PostCG areas with broader extent. This study showed that fMRI motor mapping was locationally well correlated to the activation of M1/S1 by ECS, but the spatial extent was not concordant. In addition, the involvement of SMA, PM/PPC, and the cerebellum in simple voluntary movement was also suggested. Combination analysis of fMRI and ECS motor mapping contributes to precise localization of M1/S1.     

Functional neuroanatomy of anticipatory behavior: dissociation between sensory-driven and memory-driven systems

The ability to anticipate predictable stimuli allows faster responses. The predictive saccade (PRED) task has been shown to quickly induce such anticipatory behavior in humans. In a PRED task subjects track a visual target jumping back and forth between fixed positions at a fixed time interval. During this task, saccade latencies drop from approximately 200 ms to <80 ms as subjects anticipate target appearance. This change in saccade latency indicates that subjects' behavior shifts from being sensory driven to being memory driven. We conducted functional magnetic resonance imaging studies with 10 healthy adults performing the PRED task using a standard block design. We compared the PRED task with a visually guided saccade (VGS) task using unpredictable targets matched for number, direction and amplitude of required saccades. Our results show greater activation during the PRED task in the prefrontal, pre-supplementary motor and anterior cingulate cortices, hippocampus, mediodorsal thalamus, striatum and cerebellum. The VGS task elicited greater activation in the cortical eye fields and occipital cortex. These results demonstrate the important dissociation between sensory and predictive neural control of similar saccadic eye movements. Anticipatory behavior induced by the PRED task required less sensory-related processing activity and was subserved by a distributed cortico-subcortical memory system including prefronto-striatal circuitry.     

The size of corpus callosum correlates with functional activation of medial motor cortical areas in bimanual and unimanual movements

Effects of the size of corpus callosum measured from in vivo magnetic resonance imaging (MRI) recordings on cortical activations evaluated using functional MRI (fMRI) were analyzed during motor tasks. Twelve right-handed men performed unilateral finger movements and bilateral movements either with or without a temporal delay between left and right fingers. The size of the rostral part of corpus callosum and the anterior and posterior callosal truncus explained 11.9 and 15.2% of activation in the mesial frontal cortex in unimanual left and right finger movements, respectively. In bimanual simultaneous movements, 34.2% of the activated voxels in the mesial frontal cortex were related to the size of corpus callosum. In bimanual movements in which left finger movement preceded the onset of the right finger movement, the callosal size accounted for 88.7% of activation in the mesial frontal cortex. In contrast, when the right finger movement preceded the left, callosal size accounted for only 31.3% of the mesial frontal cortex activation. The correlations between callosal parameters and activation over the lateral cortex were sparse and occurred only in bimanual movements. The results suggest that corpus callosum modulates the activity of the supplementary motor and cingulate cortical areas depending on temporal complexity of bimanual movements.     

Somatosensory, motor, and reaching/grasping responses to direct electrical stimulation of the human cingulate motor areas

OBJECT: Surgery for frontal lobe drug-resistant epilepsies is often limited by the apparent widespread distribution of the epileptogenic zone. Recent advances in the parcellation of the medial premotor cortex give the opportunity to reconsider "seizures of the supplementary motor area" (SMA), and to assess the contribution of cingulate motor areas (CMAs), SMA proper (SMAp), and pre-SMA to the symptomatology of premotor seizures. METHODS: The authors reviewed the results of extraoperative electrical stimulation (ES) applied in 52 candidates for epilepsy surgery who underwent stereotactic intracerebral electroencephalographic recordings, focusing on ES of the different medial premotor fields; that is, the anterior and posterior CMA, the SMAp, and the pre-SMA. The ES sites were localized by superposition of the postoperative lateral skull x-ray and the preoperative sagittal MR imaging studies. RESULTS: Among 94 electrodes reaching the medial premotor wall, 57 responses were obtained from the anterior CMA (13 cases), the posterior CMA (11), the pre-SMA (18), and the SMAp (15). The ES of the pre-SMA and SMAp gave rise most often to a combination of motor (31 cases), speech-related (22), or somatosensory (3) elementary symptoms. The ES of the CMA yielded simple (17 of 24) more often than complex responses (7 of 24), among which sensory symptoms (7) were overrepresented. Irrepressible exploratory reaching/grasping movements were elicited at the vicinity of the cingulate sulcus, from the anterior CMA (3 cases) or the pre-SMA (1). Clinical responses to ES were not predictive of the postoperative neurological outcome. CONCLUSIONS: These findings might be helpful in epilepsy surgery candidates, to better target investigation of the CMA, pre-SMA, and SMAp, and therefore to provide a better understanding of premotor seizures.     

Role of the medial part of the intraparietal sulcus in implementing movement direction

The contribution of the posterior parietal cortex (PPC) to visually guided movements has been originally inferred from observations made in patients suffering from optic ataxia. Subsequent electrophysiological studies in monkeys and functional imaging data in humans have corroborated the key role played by the PPC in sensorimotor transformations underlying goal-directed movements, although the exact contribution of this structure remains debated. Here, we used transcranial magnetic stimulation (TMS) to interfere transiently with the function of the left or right medial part of the intraparietal sulcus (mIPS) in healthy volunteers performing visually guided movements with the right hand. We found that a "virtual lesion" of either mIPS increased the scattering in initial movement direction (DIR), leading to longer trajectory and prolonged movement time, but only when TMS was delivered 100-160 ms before movement onset and for movements directed toward contralateral targets. Control experiments showed that deficits in DIR consequent to mIPS virtual lesions resulted from an inappropriate implementation of the motor command underlying the forthcoming movement and not from an inaccurate computation of the target localization. The present study indicates that mIPS plays a causal role in implementing specifically the direction vector of visually guided movements toward objects situated in the contralateral hemifield.     

The cross-modal interaction between pain-related and saccade-related cerebral activation: a preliminary study by event-related functional magnetic resonance imaging

Pain-related cerebral activation in functional magnetic resonance imaging shows less consistent signals that decay earlier than in conventional task-related activation. This may result from pain's top-down inhibition mediated by cognitive or hemodynamic interaction that could affect activation by other modalities. Using event-related functional magnetic resonance imaging, we examined whether pain affects cerebral activation by a saccade task through such cross-modal interaction. Six right-handed volunteers underwent whole-brain echo-planar imaging on a 3.0 T magnetic resonance imaging scanner while they received thermal pain stimulus at 50 degrees C on the right forearm (P; n = 6), performed a visually guided saccade task (V; n = 6), and went through a simultaneous pain-plus-saccade paradigm (PV; n = 5). Averaged functional activation maps were synthesized and signal time courses were analyzed at activation clusters. P activated the bilateral secondary somatosensory cortex (S2). V activated the posterior, supplementary, frontal eye fields, and visual areas. PV enhanced the S2 activation and activated additional pain-related areas, including the bilateral premotor area, right insula, anterior, and posterior cingulate cortices. In contrast, V-related activation was attenuated in PV. We propose that pain caused cross-modal suppression on the oculomotor activity and that an oculomotor task enhanced pain-related activation by triggering attention toward pain. IMPLICATIONS: Pain-related cerebral activation is enhanced by attention toward pain. It may involve top-down suppression over the unrelated neural networks of saccade.     

Cortical control of visually guided reaching: evidence from patients with optic ataxia

The dorsal stream of visual information processing connecting V1 to the parietal cortex is thought to provide a fast control of visually guided reaching. Important for this assumption was the observation that in both the monkey and the human, parietal lesions may provoke disturbance of visually goal-directed hand movements. In the human, severe misreaching termed 'optic ataxia' has been ascribed to lesions of the superior parietal lobule (SPL) and/or the intraparietal sulcus. Using new tools for lesion analysis, here we re-evaluated this view investigating the typical lesion location in a large group of unilateral stroke patients with optic ataxia, collected over a time period of 15 years. We found no evidence for the assumption that disruption of visually guided reaching in humans is associated with a lesion typically centering on the SPL on the convexity. In both left and right hemispheres, we found optic ataxia associated with a lesion overlap that affected the lateral cortical convexity at the occipito-parietal junction, i.e. the junction between the inferior parietal lobule (IPL) and superior occipital cortex and--in the left hemisphere even more posteriorly--also the junction between occipital cortex and the SPL. Via the underlying parietal white matter, the lesion overlap extended in both hemispheres to the medial cortical aspect, where it affected the precuneus close to the occipito-parietal junction. These lateral and medial structures seem to be integral to the fast control of visually guided reaching in humans.     

Hemispheric asymmetry of frequency-dependent suppression in the ipsilateral primary motor cortex during finger movement: a functional magnetic resonance imaging study

Electrophysiological studies have suggested that the activity of the primary motor cortex (M1) during ipsilateral hand movement reflects both the ipsilateral innervation and the transcallosal inhibitory control from its counterpart in the opposite hemisphere, and that their asymmetry might cause hand dominancy. To examine the asymmetry of the involvement of the ipsilateral motor cortex during a unimanual motor task under frequency stress, we conducted block-design functional magnetic resonance imaging with 22 normal right-handed subjects. The task involved visually cued unimanual opponent finger movement at various rates. The contralateral M1 showed symmetric frequency-dependent activation. The ipsilateral M1 showed task-related deactivation at low frequencies without laterality. As the frequency of the left-hand movement increased, the left M1 showed a gradual decrease in the deactivation. This data suggests a frequency-dependent increased involvement of the left M1 in ipsilateral hand control. By contrast, the right M1 showed more prominent deactivation as the frequency of the right-hand movement increased. This suggests that there is an increased transcallosal inhibition from the left M1 to the right M1, which overwhelms the right M1 activation during ipsilateral hand movement. These results demonstrate the dominance of the left M1 in both ipsilateral innervation and transcallosal inhibition in right-handed individuals.     

The representation of blinking movement in cingulate motor areas: a functional magnetic resonance imaging study

Recent anatomical evidence from nonhuman primates indicates that cingulate motor areas (CMAs) play a substantial role in the cortical control of upper facial movement. Using event-related functional magnetic resonance imaging in 10 healthy subjects, we examined brain activity associated with volitional eye closure involving primarily the bilateral orbicularis oculi. The findings were compared with those from bimanual tapping, which should identify medial frontal areas nonsomatotopically or somatotopically related to bilateral movements. In a group-level analysis, the blinking task was associated with rostral cingulate activity more strongly than the bimanual tapping task. By contrast, the bimanual task activated the caudal cingulate zone plus supplementary motor areas. An individual-level analysis indicated that 2 foci of blinking-specific activity were situated in the cingulate or paracingulate sulcus: one close to the genu of the corpus callosum (anterior part of rostral cingulate zone) and the posterior part of rostral cingulate zone. The present data support the notion that direct cortical innervation of the facial subnuclei from the CMAs might control upper face movement in humans, as previously implied in nonhuman primates. The CMAs may contribute to the sparing of upper facial muscles after a stroke involving the lateral precentral motor regions.     

Preoperative mapping of the supplementary motor area in patients harboring tumors in the medial frontal lobe

OBJECT: Injury to the supplementary motor area (SMA) is thought to be responsible for transient motor and speech deficits following resection of tumors involving the medial frontal lobe. Because direct intraoperative localization of SMA is difficult, the authors hypothesized that functional magnetic resonance (fMR) imaging might be useful in predicting the risk of postoperative deficits in patients who undergo resection of tumors in this region. METHODS: Twelve patients who had undergone fMR imaging mapping while performing speech and motor tasks prior to excision of their tumor, that is, based on anatomical landmarks involving the SMA, were included in this study. The distance between the edge of the tumor and the center of SMA activation was measured and was correlated with the risk of incurring postoperative neurological deficits. In every patient, SMA activation was noted in the superior frontal gyrus on preoperative fMR imaging. Two speech and two motor deficits typical of SMA injury were observed in three of the 12 patients. The two speech deficits occurred in patients with tumors involving the dominant hemisphere, whereas one of the motor deficits occurred in a patient with a tumor in the nondominant hemisphere. The risk of developing a postoperative speech or motor deficit was 100% when the distance between the SMA and the tumor was 5 mm or less. When the distance between SMA activation and the lesion was greater than 5 mm, the risk of developing a motor or a speech deficit was 0% (p = 0.0007). CONCLUSIONS: Early data from this study indicated that fMR imaging might be useful in localizing the SMA and in determining the risk of postoperative deficits in patients who undergo resection of tumors located in the medial frontal lobe.     

Cortical areas involved in virtual movement of phantom limbs: comparison with normal subjects

OBJECTIVE: To demonstrate that amputees performing "virtual" movements of their amputated limb activate cortical areas previously devoted to their missing limb, we studied amputees with functional magnetic resonance imaging (fMRI) and positron emission tomographic (PET) scans and compared the results with those of normal volunteers performing imaginary movements during fMRI acquisitions. METHODS: Ten amputees (age range, 33-92 yr; average age, 49 yr; six men and four women; eight upper-limb and two lower-limb amputations) able to move their phantom limb at will were studied by fMRI (all patients) and PET scan (seven patients). The time between amputation and fMRI and PET studies ranged from 1 to 27 years (average, 13 yr). Patients were asked to perform virtual movements of the amputated limb and normal movements of the contralateral normal limb according to the functional images acquisition procedure. Movements of the stump were also used to differentiate stump cortical areas from virtual movement-activated areas. Ten right-handed volunteers, age- and sex-matched to the amputees, were also studied by fMRI. All volunteers were asked to perform four tasks during their fMRI study: imaginary movements of their right arm (1 task) and foot (1 task) and real movements of their left arm (1 task) and foot (1 task). RESULTS: In amputees, virtual movements of the missing limbs produced contralateral primary sensorimotor cortex activation on both fMRI and PET scans. These activation areas, different from the stump activation areas, were similar in location to contralateral normal limb-activated areas. Quantitatively, in two amputees who claimed to be able to perform both slow and fast virtual movements, regional cerebral blood flow measured by PET scan in the precentral gyrus increased significantly during fast movements in comparison with slow virtual movements. In normal subjects, significant differences between real versus imaginary fMRI activations were found (for both foot and hand movements); imaginary right hand and foot tasks activated primarily the contralateral supplementary motor areas, with no significant activation detected in the contralateral precentral or postcentral gyri. CONCLUSION: Primary sensorimotor cortical areas can be activated by phantom-limb movements and thus can be considered functional for several years or decades after amputation. In this study, we found that the location of the activation of these areas is comparable to that of activations produced by normal movements in control subjects or in amputees.     

What disconnection tells about motor imagery: evidence from paraplegic patients

Brain activation during motor imagery has been the subject of a large number of studies in healthy subjects, leading to divergent interpretations with respect to the role of descending pathways and kinesthetic feedback on the mental rehearsal of movements. We investigated patients with complete spinal cord injury (SCI) to find out how the complete disruption of motor efferents and sensory afferents influences brain activation during motor imagery of the disconnected feet. Eight SCI patients underwent behavioral assessment and functional magnetic resonance imaging. When compared to a healthy population, stronger activity was detected in primary and all non-primary motor cortical areas and subcortical regions. In paraplegic patients the primary motor cortex was consistently activated, even to the same degree as during movement execution in the controls. Motor imagery in SCI patients activated in parallel both the motor execution and motor imagery networks of healthy subjects. In paraplegics the extent of activation in the primary motor cortex and in mesial non-primary motor areas was significantly correlated with the vividness of movement imagery, as assessed by an interview. The present findings provide new insights on the neuroanatomy of motor imagery and the possible role of kinesthetic feedback in the suppression of cortical motor output required during covert movements.     

Brain and behavior: a task-dependent eye movement study

Recent electrophysiological and behavioral studies have found similarities in the neurology of pursuit and saccadic eye movements. In a previous study on eye movements using closely matched paradigms for pursuit and saccades, we revealed that both exhibit bimodal distributions of latency to predictable (PRD) and randomized (RND) stimuli; however, the latency to each type of stimulus was different, and there was more segregation of latencies in saccades than pursuit (Burke MR, Barnes GR. 2006. Quantitative differences in smooth pursuit and saccadic eye movements in humans. Exp Brain Res. 175(4):596-608). To investigate the brain areas involved in these tasks, and to search for correlates of behavior, we used functional magnetic resonance imaging during equivalent PRD and RND target presentations. In the contrast pursuit > saccades, which reflects velocity-dependent versus position-dependent activities, respectively, we found higher activation in the dorsolateral prefrontal cortex (DLPFC) for pursuit and in the frontopolar region for saccades. In the contrast RND > PRD, which principally reflects activation related to visually driven versus memory-driven responses, respectively, we found a higher sustained level of activation in the frontal eye fields during visually guided eye movements. The reverse contrast revealed higher activity for the memory-guided responses in the supplementary eye fields and the superior parietal lobe. In addition, we found learning-related activation during the PRD condition in visual area V5, the DLPFC, and the cerebellum.