Motor Cortical Representation Research Articles

TMS brain mapping of the pharyngeal cortical representation in healthy subjects

BackgroundBrain mapping is fundamental to understanding brain organization and function. However, a major drawback to the traditional Brodmann parcellation technique is the reliance on the use of postmortem specimens. It has therefore historically been difficult to make any comparison regarding functional data from different regions or hemispheres within the same individual. Moreover, this method has been significant limited by subjective boundaries and classification criteria and therefore suffer from reproducibility issues. The development of transcranial magnetic stimulation (TMS) offers an alternative approach to brain mapping, specifically the motor cortical regions by eliciting quantifiable functional reactions. ObjectiveTo precisely describe the motor cortical topographic representation of pharyngeal constrictor musculature using TMS and to further map the brain for use as a tool to study brain plasticity. Methods51 healthy subjects (20 male/31 female, 19–26 years old) were tested using single-pulse TMS combined with intraluminal catheter-guided high-resolution manometry and a standardized grid cap. We investigated various parameters of the motor-evoked potential (MEP) that include the motor map area, amplitude, latency, center of gravity (CoG) and asymmetry index. ResultsCortically evoked response latencies were similar for the left and right hemispheres at 6.79 ± 0.22 and 7.24 ± 0.27 ms, respectively. The average scalp positions (relative to the vertex) of the pharyngeal motor cortical representation were 10.40 ± 0.19 (SE) cm medio-lateral and 3.20 ± 0.20 (SE) cm antero-posterior in the left hemisphere and 9.65 ± 0.24 (SE) cm medio-lateral and 3.18 ± 0.23 (SE) cm antero-posterior in the right hemisphere. The mean motor map area of the pharynx in the left and right hemispheres were 9.22 ± 0.85(SE) cm2and 10.12 ± 1.24(SE) cm2, respectively. The amplitudes of the MEPs were 35.94 ± 1.81(SE)uV in the left hemisphere and 34.49 ± 1.95(SE)uV in the right hemisphere. By comparison, subtle but consistent differences in the degree of the bilateral hemispheric representation were also apparent both between and within individuals. ConclusionThe swallowing musculature has a bilateral motor cortical representation across individuals, but is largely asymmetric within single subjects. These results suggest that TMS mapping using a guided intra-pharyngeal EMG catheter combined with a standardized gridded cap might be a useful tool to localize brain function/dysfunction by linking brain activation to the corresponding physical reaction.

Fast Electrophysiological Mapping of Rat Cortical Motor Representation on a Time Scale of Minutes during Skin Stimulation

The topographic map of motor cortical representation, called the motor map, is not invariant, but can be altered by motor learning, neurological injury, and functional recovery from injury. Although much attention has been paid to short-term changes of the motor map, robust measures have not been established. The existing mapping methods are time-consuming, and the obtained maps are confounded by time preference. The purpose of this study was to examine the dynamics of the motor map on a timescale of minutes during transient somatosensory input by a fast motor mapping technique. We applied 32-channel micro-electrocorticographic electrode arrays to the rat sensorimotor cortex for cortical stimulation, and the topographic profile of motor thresholds in forelimb muscle was identified by fast motor mapping. Sequential motor maps were obtained every few minutes before, during, and just after skin stimulation to the dorsal forearm using a wool buff. During skin stimulation, the motor map expanded and the center of gravity of the map was shifted caudally. The expansion of the map persisted for at least a few minutes after the end of skin stimulation. Although the motor threshold of the hotspot was not changed, the area in which it was decreased appeared caudally to the hotspot, which may be in the somatosensory cortex. The present study demonstrated rapid enlargement of the forelimb motor map in the order of a few minutes induced by skin stimulation. This helps to understand the spatial dynamism of motor cortical representation that is modulated rapidly by somatosensory input.

Persistent Reductions in Strength of Sensorimotor Circuits Governing Injured Leg After ACL Rupture

Traumatic peripheral injury, like ACL rupture, may alter neurobiological structure and function, with regional reductions in sensorimotor circuit excitability and altered activity patterns in the prefrontal cortex. PURPOSE: To examine the long-term neurobiological consequences of ACL rupture on cortical silent periods (CSPs) in the motor cortical (M1) representations of the vastus lateralis (VL). METHODS: Nine women with a history of unilateral ACL rupture, repair and rehabilitation (3.3 ± 1.2 years prior) participated in the study. Maximal voluntary isometric contraction force (MVIC) was obtained for each leg during a bilateral, closed kinetic chain movement. Active stimulus response curves were produced at 15% MVIC. Biphasic single pulse transcranial magnetic stimulation (TMS) was delivered to the left or right VL hotspot at 40, 50, 60, 70, 80, and 90% stimulator output (SO). Five pulses were delivered during each 25s contraction, with 30s rest between contractions. SO order and leg were randomized. Contralateral CSPs were measured from TMS stimulus onset to the visual resumption of muscle contractile activity. Responses to each leg-specific SO were averaged for each subject and analyzed via two-way repeated measures ANOVA with Fisher’s LSD pairwise comparisons. RESULTS: Because CSPs were consistently produced above 70% SO, quantitative analysis was limited to 70, 80, and 90% SO. Significant main effects were observed for SO (p=0.001) and Leg (p=0.026). CSP duration increased in parallel with SO intensity (80% vs. 70% Δ=32.1ms, p=0.002; 90% vs. 70% Δ=54.5ms, p=0.002; 90% vs. 80% Δ=22.4ms, p=0.015). CSPs were generally longer in the injured leg (Δ=21.6ms, p=0.026). At 70 and 80% SO, CSPs were longer in the injured leg (70% SO: 25.8ms Δ, p=0.017; 80% SO: 18.3ms Δ, p=0.026; 90% SO: 20.6ms Δ, p=0.099). A trend of increased CSP duration at 90% SO may reflect ceiling effects in the silent period of the injured leg. CONCLUSIONS: Injured-leg M1 representation stimulation increased CSP durations compared to the uninjured leg. These deficits persisted years after rehabilitation, and were reproducibly detected during bilateral closed kinetic chain movements at 15% MVIC and SOs above 70%. Our observations indicate long-term reductions in the strength of the sensorimotor circuits governing the injured leg.

Effect of repetitive transcranial magnetic stimulation combined with robot-assisted training on wrist muscle activation post-stroke

ObjectiveTo compare the effects of active assisted wrist extension training, using a robotic exoskeleton (RW), with simultaneous 5 Hz (rTMS + RW) or Sham rTMS (Sham rTMS + RW) over the ipsilesional extensor carpi radialis motor cortical representation, on voluntary wrist muscle activation following stroke. MethodsThe two training conditions were completed at least one week apart in 13 participants >1-year post-stroke. Voluntary wrist extensor muscle activation (motor unit (MU) recruitment thresholds and firing rate modulation in a ramp-hold handgrip task), ipsilesional corticospinal excitability (motor evoked potential [MEP] amplitude) and transcallosal inhibition were measured Pre- and Post-training. ResultsFor MUs active both Pre and Post training, greater reductions in recruitment thresholds were found Post rTMS + RW training (p = 0.0001) compared to Sham rTMS + RW (p = 0.16). MU firing rate modulation increased following both training conditions (p = 0.001). Ipsilesional MEPs were elicited Pre and Post in only 5/13 participants. No significant changes were seen in ipsilesional corticospinal excitability and transcallosal inhibition measures (p > 0.05). ConclusionsFollowing a single rTMS + RW session in people >1-year post-stroke, changes were found in voluntary muscle activation of wrist extensor muscles. Alterations in ipsilesional corticospinal or interhemispheric excitability were not detected. SignificanceThe effects of rTMS + RW on muscle activation warrant further investigation as post-stroke rehabilitation strategy.

Study of cortical motor representation and cortical excitability in refractory neuropathic pain

Study of cortical motor representation and cortical excitability in refractory neuropathic pain

High-intensity transcranial magnetic stimulation reveals differential cortical contributions to prepared responses.

Corticospinal output pathways have typically been considered to be the primary driver for voluntary movements of the hand/forearm; however, more recently, reticulospinal drive has also been implicated in the production of these movements. Although both pathways may play a role, the reticulospinal tract is thought to have stronger connections to flexor muscles than to extensors. Similarly, movements involuntarily triggered via a startling acoustic stimulus (SAS) are believed to receive greater reticular input than voluntary movements. To investigate a differential role of reticulospinal drive depending on movement type or acoustic stimulus, corticospinal drive was transiently interrupted using high-intensity transcranial magnetic stimulation (TMS) applied during the reaction time (RT) interval. This TMS-induced suppression of cortical drive leads to RT delays that can be used to assess cortical contributions to movement. Participants completed targeted flexion and extension movements of the wrist in a simple RT paradigm in response to a control auditory go signal or SAS. Occasionally, suprathreshold TMS was applied over the motor cortical representation for the prime mover. Results revealed that TMS significantly increased RT in all conditions. There was a significantly longer TMS-induced RT delay seen in extension movements than in flexion movements and a greater RT delay in movements initiated in response to control stimuli compared with SAS. These results suggest that the contribution of reticulospinal drive is larger for wrist flexion than for extension. Similarly, movements triggered involuntarily by an SAS appear to involve greater reticulospinal drive, and relatively less corticospinal drive, than those that are voluntarily initiated. NEW & NOTEWORTHY Through the use of the transcranial magnetic stimulation-induced silent period, we provide novel evidence for a greater contribution of reticulospinal drive, and a relative decrease in corticospinal drive, to movements involuntarily triggered by a startle compared with voluntary movements. These results also provide support for the notion that both cortical and reticular structures are involved in the neural pathway underlying startle-triggered movements. Furthermore, our results indicate greater reticulospinal contribution to wrist flexion than extension movements.

Are age-related changes in cortical motor representations linked with facilitation/inhibition in the primary motor cortex?

Are age-related changes in cortical motor representations linked with facilitation/inhibition in the primary motor cortex?

Alterations in Motor Cortical Representation of Muscles Following Incomplete Spinal Cord Injury in Humans.

(1) Background: The primary motor cortex (M1) experiences reorganization following spinal cord injury (SCI). However, there is a paucity of research comparing bilateral M1 organization in SCI and questions remain to be answered. We explored the presence of somatotopy within the M1 representation of arm muscles, and determined whether anatomical shifts in these representations occur, and investigated the symmetry in organization between the two hemispheres.; (2) Methods: Transcranial magnetic stimulation (TMS) was used to map the representation of the biceps, flexor carpi radialis and abductor pollicis brevis (APB) bilaterally in nine individuals with chronic incomplete cervical spinal cord injury and nine aged- and handed-matched uninjured controls. TMS was delivered over a 6 × 5 point grid that encompassed M1 using an intensity specific to the resting motor threshold for each muscle tested.; (3) Results: Results indicate that, compared to controls, muscle representations in SCI are shifted medially but preserve a general somatotopic arrangement, and that territory dedicated to the APB muscle is greater.; (4) Conclusions: These findings demonstrate differences in the organization of M1 between able-bodied controls and those with incomplete cervical SCI. This altered organization may have future implications in understanding the functional deficits observed in SCI and rehabilitation techniques aimed at restoring function.

Priming of grasping muscles when viewing a safety handle is diminished with age

Merely viewing objects within reachable space can activate motor cortical networks and potentiate movement. This holds potential value for smooth interaction with objects in our surroundings, and could offer an advantage for quickly generating targeted hand movements (e.g. grasping a support rail to maintain stability). The present study investigated if viewing a wall-mounted safety handle resulted in automatic activation of motor cortical networks, and if this effect changes with age. Twenty-five young adults (18–30 years) and seventeen older adults (65+ years) were included in this study. Single-pulse, transcranial magnetic stimulation was applied over the motor cortical hand representation of young and older adults shortly after they viewed a safety handle within reaching distance. Between trials, vision was occluded and the environment was unpredictably altered to reveal either a safety handle, or no handle (i.e. covered). Modulation of intrinsic hand muscle activity was evident in young adults when viewing a handle, and this was selective in terms of both the muscles activated and the time at which it emerged. By contrast, older adults failed to show any changes when viewing the safety handle. Specifically, the presence of a handle increased corticospinal activity in hand muscles of young adults when TMS was applied 120 ms after opening the goggles (p = .014), but not in the older adults (p > .954). The fact that the visual priming observed in younger adults was absent in older adults suggests that aging may diminish the ability to quickly put our visual world into automatic motor terms.

The effects of paired associative stimulation of tibial nerve-M1 cortex on forelimb dysfunction in rats with cerebral ischemic stroke and the underlying mechanisms

Objective To explore the effects and the underlying mechanisms by which paired associative stimulation (PAS) of tibial nerve electrostimulation and M1 cortex transcranial magnetic stimulation (TMS) in promoting the recovery of forelimb dysfunction in rats with cerebral ischemic stroke. Methods Resting motor thresholds of left extensor carpi radialis muscle (ECR) were determined 5 min before and 5 min, 30 min, 60 min after PAS, respectively, in 8 male Sprague-Dawley (SD) rats. Then 48 male SD rats were divided into a sham group (n=16) subject to sham surgery, an experimental group (n=32) which was further divided into a MCAO group (n=16) and a PAS group (n=16) after cerebral ischemic stroke model was established successfully by occluding the right middle cerebral artery. 24 hours after surgery, PAS consisting of left tibial nerve stimulation and right M1 cortex area TMS was applied to PAS group once daily for 7 consecutive days. The corner tests and grip strength tests were performed before and after 7 days of PAS treatment in each group. The RMTs of left ECR were determined, metabolites of the left area tissue of cervical spinal cord were measured by nuclear magnetic resonance spectrum, and expressions of Bcl-2 and Bax of left and right area tissue of cervical spinal cord enlargement were detected by Western Blot technique after 7 days of intervention. Results The average RMTs of left ECR at 5 min, 30 min, 60 min after PAS were significantly lower than those at 5 min before PAS (P<0.05). All rats in experimental group showed significant higher turning scores and lower grip strength when compared with sham group (P<0.001 or P<0.01). After PAS intervention, PAS group demonstrated lower turning scores, higher grip strength and lower RMT of left ECR as compared with MCAO group (P<0.05 or P<0.01). The expression of GABA of left cervical enlargment was significantly decreased in MCAO group when compared with the sham group (P<0.05), and there was no significant difference between MCAO group and PAS group. Meanwhile, other metabolites showed no significant difference among the three groups. The average expression level of Bcl-2 and Bax proteins in both sides of cervical spinal cord enlargment showed no significant difference among three groups either. Conclusions Tibial nerve-M1 cortex area PAS may increase the excitability of motor cortical representation of forelimbs in rats, by which PAS promotes the recovery of forelimb dysfunction in rats with cerebral ischemic stroke. Key words: Cerebral ischemic stroke; Paired associative stimulation; Resting motor threshold; GABA

Dynamics of the Cortical Motor Representation of the Extensor Digitorum Communis Muscle after Motor Imagery Training Using a Brain–Computer Interface: a Controlled Study

The mechanisms of the organization of goal-directed movements in the human arm have received insufficient study. The processes of cortical reorganization on the background of learning new skills and rehabilitation after central nervous system disease are of particular interest. Studies of the motor system and recording of neurophysiological parameters determining the kinematic characteristics of movements at the cortical level use navigated transcranial magnetic stimulation. The present study of 20 healthy volunteers randomized to study and control groups assessed resting motor thresholds, cortical motor representation zones of the extensor digitorum communis muscle in terms of areas and weighted areas, and the displacement of the centers of gravity on the background of training to motor imagery using a brain–computer interface. No significant differences were found between these parameters in the study group and the control group.

Reflections on the differential organization of mirror neuron systems for hand and mouth and their role in the evolution of communication in primates

It is now generally accepted that the motor system is not purely dedicated to the control of behavior, but also has cognitive functions. Mirror neurons have provided a new perspective on how sensory information regarding others' actions and gestures is coupled with the internal cortical motor representation of them. This coupling allows an individual to enrich his interpretation of the social world through the activation of his own motor representations. Such mechanisms have been highly preserved in evolution as they are present in humans, apes and monkeys. Recent neuroanatomical data showed that there are two different connectivity patterns in mirror neuron networks in the macaque: one is concerned with sensorimotor transformation in relation to reaching and hand grasping within the traditional parietal-premotor circuits; the second one is linked to the mouth/face motor control and the new data show that it is connected with limbic structures. The mouth mirror sector seems to be wired not only for ingestive behaviors but also for orofacial communicative gestures and vocalizations. Notably, the hand and mouth mirror networks partially overlap, suggesting the importance of hand-mouth synergies not only for sensorimotor transformation, but also for communicative purposes in order to better convey and control social signals.

Extended enhancement of corticospinal connectivity with concurrent cortical and peripheral stimulation controlled by sensorimotor desynchronization

BackgroundPairing cortical and peripheral input during motor imagery (MI)-related sensorimotor desynchronization (ERD) modulates corticospinal excitability at the cortical representation (hotspot) of the imagined movement. ObjectiveTo determine the effects of this associative stimulation protocol on the cortical motor map beyond the hotspot. MethodsIn healthy subjects, peripheral stimulation through passive hand opening by a robotic orthosis and single-pulse transcranial magnetic stimulation to the respective cortical motor representation were applied in a brain-machine interface environment. State-dependency was investigated by concurrent, delayed or non-specific stimulation with respect to ERD in the beta-band (16–22 Hz) during MI of finger extension. ResultsConcurrent stimulation led to increased excitability of an extended motor map. Delayed and non-specific stimulation led to heterogeneous changes, i.e., opposite patterns of increased excitability in either the center or the periphery of the motor map. ConclusionThese results could be instrumental in closed-loop, state-dependent stimulation in the context of neurorehabilitation.

Differential plasticity of extensor and flexor motor cortex representations following visuomotor adaptation.

Representations within the primary motor cortex (M1) are capable of rapid functional changes following motor learning, known as use-dependent plasticity. GABAergic inhibition plays a role in use-dependent plasticity. Evidence suggests a different capacity for plasticity of distal and proximal upper limb muscle representations. However, it is unclear whether the motor cortical representations of forearm flexor and extensor muscles also have different capacities for plasticity. The current study used transcranial magnetic stimulation to investigate motor cortex excitability and inhibition of forearm flexor and extensor representations before and after performance of a visuomotor adaptation task that primarily targeted flexors and extensors separately. There was a decrease in extensor and flexor motor-evoked potential (MEP) amplitude after performing the extensor adaptation, but no change in flexor and extensor MEP amplitude after performing the flexor adaptation. There was also a decrease in motor cortical inhibition in the extensor following extensor adaptation, but no change in motor cortical inhibition in the flexor muscle following flexor adaptation or either of the non-prime mover muscles. Findings suggest that the forearm extensor motor cortical representation exhibits plastic change following adaptive motor learning, and broadly support the distinct neural control of forearm flexor and extensor muscles.

Detailed somatotopy in primary motor and somatosensory cortex revealed by Gaussian population receptive fields

The relevance of human primary motor cortex (M1) for motor actions has long been established. However, it is still unknown how motor actions are represented, and whether M1 contains an ordered somatotopy at the mesoscopic level. In the current study we show that a detailed within-limb somatotopy can be obtained in M1 during finger movements using Gaussian population Receptive Field (pRF) models. Similar organizations were also obtained for primary somatosensory cortex (S1), showing that individual finger representations are interconnected throughout sensorimotor cortex. The current study additionally estimates receptive field sizes of neuronal populations, showing differences between finger digit representations, between M1 and S1, and additionally between finger digit flexion and extension. Using the Gaussian pRF approach, the detailed somatotopic organization of M1 can be obtained including underlying characteristics, allowing for the in-depth investigation of cortical motor representation and sensorimotor integration.

Distributed representation of pelvic floor muscles in human motor cortex

Human motor cortex can activate pelvic floor muscles (PFM), but the motor cortical representation of the PFM is not well characterized. PFM representation is thought to be focused in the supplementary motor area (SMA). Here we examine the degree to which PFM representation is distributed between SMA and the primary motor cortex (M1), and how this representation is utilized to activate the PFM in different coordination patterns. We show that two types of coordination patterns involving PFM can be voluntarily accessed: one activates PFM independently of synergists and a second activates PFM prior to and in proportion with synergists (in this study, the gluteus maximus muscle – GMM). Functional magnetic resonance imaging (fMRI) showed that both coordination patterns involve overlapping activation in SMA and M1, suggesting the presence of intermingled but independent neural populations that access the different patterns. Transcranial magnetic stimulation (TMS) confirmed SMA and M1 representation for the PFM. TMS also showed that, equally for SMA and M1, PFM can be activated during rest but GMM can only be activated after voluntary drive to GMM, suggesting that these populations are distinguished by activation threshold. We conclude that PFM representation is broadly distributed in SMA and M1 in humans.

Altered somatosensory processing in Parkinson's disease and modulation by dopaminergic medications

BackgroundSomatosensory abnormalities contribute to the pathophysiology of Parkinson's disease (PD). The goal of this study was to identify abnormalities in the tactile-evoked activation of the somatosensory and motor cortices in PD, and in a sensorimotor circuit that traverses both of these cortical loci. The second goal was to investigate the impact of dopaminergic medication on these measures. MethodsIndividuals with PD (n = 10, age 61 ± 8 years) and aged-matched controls (n = 11, age 52.3 ± 10.4 years) were studied. PD subjects were studied on and off dopaminergic medications. Using high-resolution functional magnetic resonance, imaging data was acquired over the primary somatosensory and motor cortices during passively delivered, computer-automated tactile stimulation of digits 2 and 5 of the more affected hand in PD and the analogous hand in controls. Short and long-latency afferent inhibition (SAI, LAI) were assessed via median nerve stimulation followed by transcranial magnetic stimulation over the motor cortical representation of the first dorsal interosseous muscle. ResultsCompared to controls, PD subjects demonstrated diminished activation within the somatosensory cortex, reduced LAI and normal SAI, of which all were insensitive to dopaminergic medications. In addition to improving motor symptoms, dopaminergic medications reduced the hyperactivity observed within primary motor cortex in PD. ConclusionsSomatosensory processing is deficient in PD. Reduction in tactile-evoked activation within primary motor cortex may contribute to improvement in motor symptoms with dopaminergic medications.

S183. The dynamics of the m. extensor digitorum communis cortical representation after motor imagery training sessions using brain-computer interface: Controlled study

Introduction Mechanisms of goal oriented movements in human arm are not clearly understood. Cortex reorganization after motor learning is of special interest. nTMS is widely used in the field of research related to mechanisms of movement on the cortical level. Mental practice with motor imagery (MI) paradigm is noted for its ability to activate motor system-related areas and to cause neuroplastic changes in cortical motor organization. Brain computer interfaces are used to enhance mental practice providing appropriate feedback in the form of robotic or exoskeleton external devices. Methods The aim of our study was to investigate the reorganization of cortical motor representation of extensor digitorum communis muscle after motor imagery training course enhanced by noninvasive EEG-based brain-computer interface (BCI) with exoskeleton of the hand in healthy subjects. In the current study thirty-four healthy subjects (nine of them were left-handed) were enrolled and randomized into main and control group. Every volunteer completed 10 training sessions of BCI-enhanced motor imagery. Mapping of m. extensor digitorum communis of dominant hand cortical motor representation with the evaluation of area, weighted area and the location of centers of gravity using self-designed program software was performed before and after 10 training sessions. Cortical representation areas were visualised using spherical Voronoi tessellation. Results No significant differences in the amplitude of motor thresholds (MT in rest 57.71 and 54.18, p > 0.05, MT during MI 53.06 and 51.76, p > 0.05), cortical motor representation area and weighted area were seen in both groups before intervention (371.227 and 468.719 mm2, p > 0.05; 102461.066 and 133264.876 mm2 × uV, p > 0.05). One way ANOVA test revealed no significant change in parameters of cortical motor representations in the main group comparing to control after intervention (centers of gravity displacement F = 0.360, p = 0.553, area of cortical motor representation of m.extensor digitorum communis F = 3.599, p = 0.068; weighted area F = 1.522, p = 0.227). Conclusion No significant differences in nTMS parameters of cortical motor representation of target muscle were shown between main and control group. This data could be partly explained by extremely high interindividual variability of TMS parameters, limited sample size and limitations of methodology. Futher research is needed. Funding is provided by grant RFBR N 16-04-01766.

Accurate motor mapping in awake common marmosets using micro-electrocorticographical stimulation and stochastic threshold estimation

Objective. Motor map has been widely used as an indicator of motor skills and learning, cortical injury, plasticity, and functional recovery. Cortical stimulation mapping using epidural electrodes is recently adopted for animal studies. However, several technical limitations still remain. Test-retest reliability of epidural cortical stimulation (ECS) mapping has not been examined in detail. Many previous studies defined evoked movements and motor thresholds by visual inspection, and thus, lacked quantitative measurements. A reliable and quantitative motor map is important to elucidate the mechanisms of motor cortical reorganization. The objective of the current study was to perform reliable ECS mapping of motor representations based on the motor thresholds, which were stochastically estimated by motor evoked potentials and chronically implanted micro-electrocorticographical (µECoG) electrode arrays, in common marmosets. Approach. ECS was applied using the implanted µECoG electrode arrays in three adult common marmosets under awake conditions. Motor evoked potentials were recorded through electromyographical electrodes implanted in upper limb muscles. The motor threshold was calculated through a modified maximum likelihood threshold-hunting algorithm fitted with the recorded data from marmosets. Further, a computer simulation confirmed reliability of the algorithm. Main results. Computer simulation suggested that the modified maximum likelihood threshold-hunting algorithm enabled to estimate motor threshold with acceptable precision. In vivo ECS mapping showed high test-retest reliability with respect to the excitability and location of the cortical forelimb motor representations. Significance. Using implanted µECoG electrode arrays and a modified motor threshold-hunting algorithm, we were able to achieve reliable motor mapping in common marmosets with the ECS system.

Communication calls produced by electrical stimulation of four structures in the guinea pig brain

One of the main central processes affecting the cortical representation of conspecific vocalizations is the collateral output from the extended motor system for call generation. Before starting to study this interaction we sought to compare the characteristics of calls produced by stimulating four different parts of the brain in guinea pigs (Cavia porcellus). By using anaesthetised animals we were able to reposition electrodes without distressing the animals. Trains of 100 electrical pulses were used to stimulate the midbrain periaqueductal grey (PAG), hypothalamus, amygdala, and anterior cingulate cortex (ACC). Each structure produced a similar range of calls, but in significantly different proportions. Two of the spontaneous calls (chirrup and purr) were never produced by electrical stimulation and although we identified versions of chutter, durr and tooth chatter, they differed significantly from our natural call templates. However, we were routinely able to elicit seven other identifiable calls. All seven calls were produced both during the 1.6 s period of stimulation and subsequently in a period which could last for more than a minute. A single stimulation site could produce four or five different calls, but the amygdala was much less likely to produce a scream, whistle or rising whistle than any of the other structures. These three high-frequency calls were more likely to be produced by females than males. There were also differences in the timing of the call production with the amygdala primarily producing calls during the electrical stimulation and the hypothalamus mainly producing calls after the electrical stimulation. For all four structures a significantly higher stimulation current was required in males than females. We conclude that all four structures can be stimulated to produce fictive vocalizations that should be useful in studying the relationship between the vocal motor system and cortical sensory representation.