Left Ventral Premotor Cortex Research Articles

Diffusion imaging of cerebral white matter in persons who stutter: evidence for network-level anomalies.

Deficits in brain white matter have been a main focus of recent neuroimaging studies on stuttering. However, no prior study has examined brain connectivity on the global level of the cerebral cortex in persons who stutter (PWS). In the current study, we analyzed the results from probabilistic tractography between regions comprising the cortical speech network. An anatomical parcellation scheme was used to define 28 speech production-related ROIs in each hemisphere. We used network-based statistic (NBS) and graph theory to analyze the connectivity patterns obtained from tractography. At the network-level, the probabilistic corticocortical connectivity from the PWS group were significantly weaker than that from persons with fluent speech (PFS). NBS analysis revealed significant components in the bilateral speech networks with negative correlations with stuttering severity. To facilitate comparison with previous studies, we also performed tract-based spatial statistics (TBSS) and regional fractional anisotropy (FA) averaging. Results from tractography, TBSS and regional FA averaging jointly highlight the importance of several regions in the left peri-Rolandic sensorimotor and premotor areas, most notably the left ventral premotor cortex (vPMC) and middle primary motor cortex, in the neuroanatomical basis of stuttering.

P 171. Bihemispheric motor cortex stimulation in older adults induces modulations of resting state and task-related activity

Bihemispheric transcranial direct current stimulation (“dual” tDCS) of primary motor cortices has been described to enhance motor learning in healthy subjects and to facilitate motor recovery after stroke. In order to investigate the neural correlates of its mode of action, we compared different tDCS montages in a group of healthy older adults in a cross-over design (‘dual’ vs. ‘anodal’ vs. ‘sham’). 20 subjects (mean age 68.7 ± 4.7 years, all right-handed) underwent tDCS and simultaneous MRI at 3T, including resting state fMRI and a choice reaction time task. In the task, subjects were presented with different symbols in a randomized order and required to respond with button presses using either left or right index fingers. In both active stimulation conditions, the anode was placed over left primary motor cortex (M1). The cathode was positioned over right M1 (dual) or the contralateral supraorbital region (anodal). The current was constantly delivered during resting state and task-related fMRI. Task-related fMRI analysis was carried out with SPM8; resting state data were analyzed with Lipsia using low-frequency spectral Eigenvector Centrality Mapping (ECM). Task-specific analyses revealed differential effects of the two active tDCS conditions. Compared with anodal tDCS, dual tDCS yielded stronger activations in bilateral primary motor cortices when either the left or right index fingers were used. In the resting state analysis, ECM values in left prefrontal and cingulate cortices were higher in the dual condition as compared to sham. Anodal yielded higher ECM values in the left prefrontal as well as left ventral premotor cortex when compared with sham; lower values were found in right M1 and the left precuneus. Comparing the two active tDCS conditions, increased connectivity of the cingulate cortex and decreased connectivity in the right cerebellum was found under dual compared to anodal tDCS (all p < .001, Monte Carlo-corrected). In conclusion, tDCS induced specific changes of M1 activation in task-specific activations, dependent on the electrode set-up. As a complement, the resting state analysis demonstrated altered connectivity within a multimodal network including motor cortices as well as prefrontal regions, indicating that the previously documented stronger behavioral effects of dual as compared to anodal tDCS may not be merely mediated by a “simple” add-on effect of cathodal stimulation, but rather due to complex bihemispheric network modulations.

Structural brain plasticity in Parkinson's disease induced by balance training

We investigated morphometric brain changes in patients with Parkinson's disease (PD) that are associated with balance training. A total of 20 patients and 16 healthy matched controls learned a balance task over a period of 6 weeks. Balance testing and structural magnetic resonance imaging were performed before and after 2, 4, and 6 training weeks. Balance performance was re-evaluated after ∼20 months. Balance training resulted in performance improvements in both groups. Voxel-based morphometry revealed learning-dependent gray matter changes in the left hippocampus in healthy controls. In PD patients, performance improvements were correlated with gray matter changes in the right anterior precuneus, left inferior parietal cortex, left ventral premotor cortex, bilateral anterior cingulate cortex, and left middle temporal gyrus. Furthermore, a TIME × GROUP interaction analysis revealed time-dependent gray matter changes in the right cerebellum. Our results highlight training-induced balance improvements in PD patients that may be associated with specific patterns of structural brain plasticity. In summary, we provide novel evidence for the capacity of the human brain to undergo learning-related structural plasticity even in a pathophysiological disease state such as in PD.

Computational modeling of stuttering caused by impairments in a basal ganglia thalamo-cortical circuit involved in syllable selection and initiation

Atypical white-matter integrity and elevated dopamine levels have been reported for individuals who stutter. We investigated how such abnormalities may lead to speech dysfluencies due to their effects on a syllable-sequencing circuit that consists of basal ganglia (BG), thalamus, and left ventral premotor cortex (vPMC). “Neurally impaired” versions of the neurocomputational speech production model GODIVA were utilized to test two hypotheses: (1) that white-matter abnormalities disturb the circuit via corticostriatal projections carrying copies of executed motor commands and (2) that dopaminergic abnormalities disturb the circuit via the striatum. Simulation results support both hypotheses: in both scenarios, the neural abnormalities delay readout of the next syllable’s motor program, leading to dysfluency. The results also account for brain imaging findings during dysfluent speech. It is concluded that each of the two abnormality types can cause stuttering moments, probably by affecting the same BG–thalamus–vPMC circuit.

Functional Anatomy of Writing with the Dominant Hand

While writing performed by any body part is similar in style, indicating a common program, writing with the dominant hand is particularly skilled. We hypothesized that this skill utilizes a special motor network supplementing the motor equivalence areas. Using functional magnetic resonance imaging in 13 normal subjects, we studied nine conditions: writing, zigzagging and tapping, each with the right hand, left hand and right foot. We identified brain regions activated with the right (dominant) hand writing task, exceeding the activation common to right-hand use and the writing program, both identified without right-hand writing itself. Right-hand writing significantly differed from the other tasks. First, we observed stronger activations in the left dorsal prefrontal cortex, left intraparietal sulcus and right cerebellum. Second, the left anterior putamen was required to initiate all the tested tasks, but only showed sustained activation during the right-hand writing condition. Lastly, an exploratory analysis showed clusters in the left ventral premotor cortex and inferior and superior parietal cortices were only significantly active for right-hand writing. The increased activation with right-hand writing cannot be ascribed to increased effort, since this is a well-practiced task much easier to perform than some of the other tasks studied. Because parietal-premotor connections code for particular skills, it would seem that the parietal and premotor regions, together with basal ganglia-sustained activation likely underlie the special skill of handwriting with the dominant hand.

Functional segregation in the left premotor cortex in language processing: Evidence from fMRI

Functional segregation has been revealed in the premotor cortex (PMC) and is related to motor and sensorimotor behaviors. Few data is available concerning the existence of similar segregation in the PMC during language processing. Here we correlated the roles of subregions of the left PMC in picture naming and articulation using functional magnetic resonance imaging (fMRI) and covert and overt picture naming in healthy volunteers. The results showed that the left dorsal PMC was extensively activated by covert picture naming, suggesting its recruitment in the naming network. The left ventral PMC was activated after comparison of overt vs. covert naming, suggesting its participation in articulation. These results may indicate that there is dorsal and ventral segregation of the left PMC during language processing.

Limited plastic potential of the left ventral premotor cortex in speech articulation: evidence from intraoperative awake mapping in glioma patients.

Despite previous lesional and functional neuroimaging studies, the actual role of the left ventral premotor cortex (vPMC), i.e., the lateral part of the precentral gyrus, is still poorly known. We report a series of eight patients with a glioma involving the left vPMC, who underwent awake surgery with intraoperative cortical and subcortical language mapping. The function of the vPMC, its subcortical connections, and its reorganization potential are investigated in the light of surgical findings and language outcome after resection. Electrostimulation of both the vPMC and subcortical white matter tract underneath the vPMC, that is, the anterior segment of the lateral part of the superior longitudinal fascicle (SLF), induced speech production disturbances with anarthria in all cases. Moreover, although some degrees of redistribution of the vPMC have been found in four patients, allowing its partial resection with no permanent speech disorders, this area was nonetheless still detected more medially in the precentral gyrus in the eight patients, despite its invasion by the glioma. Moreover, a direct connection of the vPMC with the SLF was preserved in all cases. Our original data suggest that the vPMC plays a crucial role in the speech production network and that its plastic potential is limited. We propose that this limitation is due to an anatomical constraint, namely the necessity for the left vPMC to remain connected to the lateral SLF. Beyond fundamental implications, such knowledge may have clinical applications, especially in surgery for tumors involving this cortico-subcortical circuit.

Increased Facilitatory Connectivity from the Pre-SMA to the Left Dorsal Premotor Cortex during Pseudoword Repetition

Previous studies have demonstrated that the repetition of pseudowords engages a network of premotor areas for articulatory planning and articulation. However, it remains unclear how these premotor areas interact and drive one another during speech production. We used fMRI with dynamic causal modeling to investigate effective connectivity between premotor areas during overt repetition of words and pseudowords presented in both the auditory and visual modalities. Regions involved in phonological aspects of language production were identified as those where regional increases in the BOLD signal were common to repetition in both modalities. We thus obtained three seed regions: the bilateral pre-SMA, left dorsal premotor cortex (PMd), and left ventral premotor cortex that were used to test 63 different models of effective connectivity in the premotor network for pseudoword relative to word repetition. The optimal model was identified with Bayesian model selection and reflected a network with driving input to pre-SMA and an increase in facilitatory drive from pre-SMA to PMd during repetition of pseudowords. The task-specific increase in effective connectivity from pre-SMA to left PMd suggests that the pre-SMA plays a supervisory role in the generation and subsequent sequencing of motor plans. Diffusion tensor imaging-based fiber tracking in another group of healthy volunteers showed that the functional connection between both regions is underpinned by a direct cortico-cortical anatomical connection.

A mediating role of the auditory dorsal pathway in selective adaptation to speech: A state-dependent transcranial magnetic stimulation study

In addition to sensory processing, recent neurobiological models of speech perception postulate the existence of a left auditory dorsal processing stream, linking auditory speech representations in the auditory cortex with articulatory representations in the motor system, through sensorimotor interaction interfaced in the supramarginal gyrus and/or the posterior part of the superior temporal gyrus. The present state-dependent transcranial magnetic stimulation study is aimed at determining whether speech recognition is indeed mediated by the auditory dorsal pathway, by examining the causal contribution of the left ventral premotor cortex, supramarginal gyrus and posterior part of the superior temporal gyrus during an auditory syllable identification/categorization task. To this aim, participants listened to a sequence of /ba/ syllables before undergoing a two forced-choice auditory syllable decision task on ambiguous syllables (ranging in the categorical boundary between /ba/ and /da/). Consistent with previous studies on selective adaptation to speech, following adaptation to /ba/, participants responses were biased towards /da/. In contrast, in a control condition without prior auditory adaptation no such bias was observed. Crucially, compared to the results observed without stimulation, single-pulse transcranial magnetic stimulation delivered at the onset of each target stimulus interacted with the initial state of each of the stimulated brain area by enhancing the adaptation effect. These results demonstrate that the auditory dorsal pathway contribute to auditory speech adaptation.

Neuroanatomical correlates of biological motion detection

Biological motion detection is both commonplace and important, but there is great inter-individual variability in this ability, the neural basis of which is currently unknown. Here we examined whether the behavioral variability in biological motion detection is reflected in brain anatomy. Perceptual thresholds for detection of biological motion and control conditions (non-biological object motion detection and motion coherence) were determined in a group of healthy human adults (n=31) together with structural magnetic resonance images of the brain. Voxel based morphometry analyzes revealed that gray matter volumes of left posterior superior temporal sulcus (pSTS) and left ventral premotor cortex (vPMC) significantly predicted individual differences in biological motion detection, but showed no significant relationship with performance on the control tasks. Our study reveals a neural basis associated with the inter-individual variability in biological motion detection, reliably linking the neuroanatomical structure of left pSTS and vPMC with biological motion detection performance.

Somatosensory-Motor Adaptation of Orofacial Actions in Posterior Parietal and Ventral Premotor Cortices

Recent studies have provided evidence for sensory-motor adaptive changes and action goal coding of visually guided manual action in premotor and posterior parietal cortices. To extend these results to orofacial actions, devoid of auditory and visual feedback, we used a repetition suppression paradigm while measuring neural activity with functional magnetic resonance imaging during repeated intransitive and silent lip, jaw and tongue movements. In the motor domain, this paradigm refers to decreased activity in specific neural populations due to repeated motor acts and has been proposed to reflect sensory-motor adaptation. Orofacial movements activated a set of largely overlapping, common brain areas forming a core neural network classically involved in orofacial motor control. Crucially, suppressed neural responses during repeated orofacial actions were specifically observed in the left ventral premotor cortex, the intraparietal sulcus, the inferior parietal lobule and the superior parietal lobule. Since no visual and auditory feedback were provided during orofacial actions, these results suggest somatosensory-motor adaptive control of intransitive and silent orofacial actions in these premotor and parietal regions.

Neural strategies for reading Japanese and Chinese sentences: A cross-linguistic fMRI study of character-decoding and morphosyntax

Japanese and Chinese share virtually identical morphographic characters invented in ancient China. Whereas modern Chinese retained the original morphographic functionality of these characters (hanzi), modern Japanese utilizes these characters (kanji) as complex syllabograms. This divergence provides a unique opportunity to systematically investigate brain strategies for sentence reading in Japanese–Chinese bi-literates. Accordingly, we investigated brain activation associated with Japanese and Chinese reading in 14 native Japanese speakers literate in Mandarin and 14 native Mandarin speakers literate in Japanese using functional magnetic resonance imaging performed on a 3T system. The activation pattern exhibited clearly distinct features specific for each language. Regardless of the subject’s native language literacy, Chinese reading activated an area significantly larger than Japanese reading, suggesting that brain processes involved in Chinese reading were much more complex than Japanese reading. Significant recruitment of corresponding cortical areas in the right hemisphere with Chinese reading was also apparent. The activation patterns associated with Japanese reading by native Japanese literates was highly consistent with previous reports, and included the left inferior frontal gyrus (IFG), left posterior temporal lobe (PTL), and left ventral premotor cortex (PMv). The activation pattern associated with Chinese reading by native Chinese literates was also highly consistent with previous reports, namely the left IFG, left PTL, left PMv, left anterior temporal lobe (ATL), and bilateral parieto occipital lobes (LPOL). The activation pattern associated with Chinese reading by native Japanese literates was virtually identical to that by native Chinese literates, whereas the activation pattern associated with Japanese reading by native Chinese literates was signified by additional activation of LPOL compared to that by native Japanese literate. The study indicated that IFG and PTL are universal language areas, while PMv is the area for decoding complex syllabograms. LPOL is the “Chinese language area,” while ATL is essential for languages with analytic morphosyntax.

The dynamics of language-related high-gamma activity assessed on a spatially-normalized brain

ObjectiveWe developed a novel technique of spatial normalization of subdural electrode positions across subjects and assessed the spatial–temporal dynamics of high-gamma activity (HGA) in the dominant hemisphere elicited by three distinct language tasks. MethodsThe normalization process was applied to 1512 subdural electrodes implanted in 21 patients with intractable epilepsy. We projected each task-related HGA profile onto a normalized brain. ResultsThe word interpretation task initially elicited HGA augmentation in the bilateral fusiform gyri at 100ms after stimulus onsets, subsequently in the left posterior middle temporal gyrus, in the left ventral premotor cortex at 200ms and in the left middle and left inferior frontal gyri at 300ms and after. The picture naming task elicited HGA augmentation in few sites in the left frontal lobe. The verb generation task elicited HGA in the left superior temporal gyrus at 100–600ms. Common HGA augmentation elicited by all three tasks was noted in the left posterior-middle temporal and left ventral premotor cortices. ConclusionsThe spatial–temporal dynamics of language-related HGA were demonstrated on a spatially-normalized brain template. SignificanceThis study externally validated the spatial and temporal dynamics of language processing suggested by previous neuroimaging and electrophysiological studies.

Spatiotemporal dynamics of brain activity during the transition from visually guided to memory-guided force control

It is well established that the prefrontal cortex is involved during memory-guided tasks whereas visually guided tasks are controlled in part by a frontal-parietal network. However, the nature of the transition from visually guided to memory-guided force control is not as well established. As such, this study examines the spatiotemporal pattern of brain activity that occurs during the transition from visually guided to memory-guided force control. We measured 128-channel scalp electroencephalography (EEG) in healthy individuals while they performed a grip force task. After visual feedback was removed, the first significant change in event-related activity occurred in the left central region by 300 ms, followed by changes in prefrontal cortex by 400 ms. Low-resolution electromagnetic tomography (LORETA) was used to localize the strongest activity to the left ventral premotor cortex and ventral prefrontal cortex. A second experiment altered visual feedback gain but did not require memory. In contrast to memory-guided force control, altering visual feedback gain did not lead to early changes in the left central and midline prefrontal regions. Decreasing the spatial amplitude of visual feedback did lead to changes in the midline central region by 300 ms, followed by changes in occipital activity by 400 ms. The findings show that subjects rely on sensorimotor memory processes involving left ventral premotor cortex and ventral prefrontal cortex after the immediate transition from visually guided to memory-guided force control.

Dynamic Visuomotor Transformation Involved with Remote Flying of a Plane Utilizes the ‘Mirror Neuron’ System

Brain regions involved with processing dynamic visuomotor representational transformation are investigated using fMRI. The perceptual-motor task involved flying (or observing) a plane through a simulated Red Bull Air Race course in first person and third person chase perspective. The third person perspective is akin to remote operation of a vehicle. The ability for humans to remotely operate vehicles likely has its roots in neural processes related to imitation in which visuomotor transformation is necessary to interpret the action goals in an egocentric manner suitable for execution. In this experiment for 3rd person perspective the visuomotor transformation is dynamically changing in accordance to the orientation of the plane. It was predicted that 3rd person remote flying, over 1st, would utilize brain regions composing the ‘Mirror Neuron’ system that is thought to be intimately involved with imitation for both execution and observation tasks. Consistent with this prediction differential brain activity was present for 3rd person over 1st person perspectives for both execution and observation tasks in left ventral premotor cortex, right dorsal premotor cortex, and inferior parietal lobule bilaterally (Mirror Neuron System) (Behaviorally: 1st>3rd). These regions additionally showed greater activity for flying (execution) over watching (observation) conditions. Even though visual and motor aspects of the tasks were controlled for, differential activity was also found in brain regions involved with tool use, motion perception, and body perspective including left cerebellum, temporo-occipital regions, lateral occipital cortex, medial temporal region, and extrastriate body area. This experiment successfully demonstrates that a complex perceptual motor real-world task can be utilized to investigate visuomotor processing. This approach (Aviation Cerebral Experimental Sciences ACES) focusing on direct application to lab and field is in contrast to standard methodology in which tasks and conditions are reduced to their simplest forms that are remote from daily life experience.

Functional Plasticity Induced by Mirror Training

Background. Mirror therapy (MT) is a promising therapeutic approach in stroke patients with severe hand paresis. Objective. The ipsilateral (contralesional) primary sensorimotor cortex (SMC) and the mirror neuron system have been suggested to play decisive roles in the MT network. The present study investigated its underlying neural plasticity. Methods. Two groups of healthy participants (n = 13 in each group) performed standardized fine motor tasks moving pegs and marbles (20 min/d for 4 days) with their right hand with either a mirror (mirror training group, MG) or a nonreflective board (control training group, CG) positioned orthogonally in front of them. The number of items moved by each hand was tested after each training session. Functional MRI (fMRI) was acquired before and after the training procedure to investigate the mirror training (MTr)-specific network by the analysis of the factors Time and Group. Results. The hand performance test of the trained right hand did not differ between the 2 groups. The untrained left hand improved significantly more in the MG compared with the CG. fMRI analysis of action observation and imitation of grasping tasks demonstrated MTr-specific activation changes within the right dorsal and left ventral premotor cortex as well as in the left SMC (SMCleft). Analysis of functional and effective connectivity showed a MTr-specific increase of functional coupling between each premotor region and the left supplementary motor area, which in turn showed an increased functional interaction with the ipsilateral SMCleft. Conclusions. MTr remodels the motor system by functionally connecting hand movement to the ipsilateral SMC. On a system level, it leads to interference of the neural circuit related to motor programming and observation of the trained hand with the illusionary movement of the untrained hand.

TMS-induced modulation of action sentence priming in the ventral premotor cortex

Despite accumulating evidence that cortical motor areas, particularly the lateral premotor cortex, are activated during language comprehension, the question of whether motor processes help mediate the semantic encoding of language remains controversial. To address this issue, we examined whether low frequency (1Hz) repetitive transcranial magnetic stimulation (rTMS) of the left ventral premotor cortex (PMv) can interfere with the comprehension of sentences describing manual actions, visual properties of manipulable and non-manipulable objects, and actions of the lips and mouth. Using a primed semantic decision task, sixteen participants were asked to determine for a given sentence whether or not an auditorily presented target word was congruent with the sentence. We hypothesized that if the left PMv is contributing semantic information that is used to comprehend action and object related sentences, then TMS applied over PMv should result in a disruption of semantic priming. Our results show that TMS reduces semantic priming, induces a shift in response bias, and increases response sensitivity, but does so only during the processing of manual action sentences. This suggests a preferential contribution of PMv to the processing of sentences describing manual actions compared to other types of sentences.

Learning to play a melody: An fMRI study examining the formation of auditory-motor associations

Interactions between the auditory and motor systems are important for music and speech, and may be especially relevant when one learns to associate sounds with movements such as when learning to play a musical instrument. However, little is known about the neural substrates underlying auditory-motor learning. This study used fMRI to investigate the formation of auditory-motor associations while participants with no musical training learned to play a melody. Listening to melodies before and after training activated the superior temporal gyrus bilaterally, but neural activity in this region was significantly reduced on the right when participants listened to the trained melody. When playing melodies and random sequences, activity in the left dorsal premotor cortex (PMd) was reduced in the late compared to early phase of training; learning to play the melody was also associated with reduced neural activity in the left ventral premotor cortex (PMv). Participants with the highest performance scores for learning the melody showed more reduced neural activity in the left PMd and PMv. Learning to play a melody or random sequence involves acquiring conditional associations between key-presses and their corresponding musical pitches, and is related to activity in the PMd. Learning to play a melody additionally involves acquisition of a learned auditory-motor sequence and is related to activity in the PMv. Together, these findings demonstrate that auditory-motor learning is related to the reduction of neural activity in brain regions of the dorsal auditory action stream, which suggests increased efficiency in neural processing of a learned stimulus.

Cognitive Neuroscience: Swapping Bodies in the Brain

A recent study has found that activity in multisensory brain areas, namely the premotor cortex, intraparietal cortex and the putamen, mirrors the vividness ofownership over a mannequin, induced by the body-swap illusion.

Speech Facilitation by Left Inferior Frontal Cortex Stimulation

SummaryElectrophysiological studies in humans and animals suggest that noninvasive neurostimulation methods such as transcranial direct current stimulation (tDCS) can elicit long-lasting [1], polarity-dependent [2] changes in neocortical excitability. Application of tDCS can have significant and selective behavioral consequences that are associated with the cortical location of the stimulation electrodes and the task engaged during stimulation [3–8]. However, the mechanism by which tDCS affects human behavior is unclear. Recently, functional magnetic resonance imaging (fMRI) has been used to determine the spatial topography of tDCS effects [9–13], but no behavioral data were collected during stimulation. The present study is unique in this regard, in that both neural and behavioral responses were recorded using a novel combination of left frontal anodal tDCS during an overt picture-naming fMRI study. We found that tDCS had significant behavioral and regionally specific neural facilitation effects. Furthermore, faster naming responses correlated with decreased blood oxygen level-dependent (BOLD) signal in Broca's area. Our data support the importance of Broca's area within the normal naming network and as such indicate that Broca's area may be a suitable candidate site for tDCS in neurorehabilitation of anomic patients, whose brain damage spares this region.