Somatotopy Research Articles

Cortical neuronal pools in primary sensory and motor regions and their functional relationship investigated non-invasively in man

Event Abstract Back to Event Cortical neuronal pools in primary sensory and motor regions and their functional relationship investigated non-invasively in man Leo Tomasevic1*, Camillo Porcaro2, Filippo Zappasodi3, Carlo Salustri1 and Franca Tecchio4 1 ISTC-CNR, Italy 2 BUIC, United Kingdom 3 G. D Annunzio University, Department of Clinical Sciences and Bioimaging , Italy 4 Ospedale Fatebenefratelli, Isola Tiberina, CNR-ISTC, Unità MEG, Italy Knowledge about the physiological organization of the areas devoted to the hand control, in terms of local connectivity and functional relationship between sensory and motor counterparts, is a cornerstone for comprehension of reorganization phenomena during learning and in reacting to pathological conditions. Through a novel cerebral source extraction method from magnetoencephalographic signals, the Functional Source Separation [1], primary cortical codes of sensorimotor dexterity were investigated: 1) in the somatosensory counterpart, through representation assessment of two fingers with different levels of functional skill (Thumb, Little finger), obtained by separately providing a passive simple sensory stimulation. In the two hemispheres, neural oscillatory activity synchronization was analysed in the characteristic frequency bands by a measure isolating the phase locking between neural network components. 2) in the motor counterpart, through assessment of cortical features related to better and worst performances. In the primary sensory cortex, in the dominant hemisphere, the phase locking selectively in the gamma band (ICC) was higher for the thumb than for the little finger and it correlated with the contra-lateral finger dexterity, scored by the Fingertip writing test. During an isometric contraction, we found that synchronous activity of primary sensory and motor areas in the high gamma band was dependent on the performance level and with low variability in the healthy population. Our data on ICC suggest the dynamic gamma band phase locking as a code for finger dexterity in the primary sensory cortex, in addition to the magnification of somatotopic maps. Moreover, connectivity in the high gamma band between primary sensory and motor cortices quantitatively estimates the continuous functional balance between primary sensory and motor areas devoted to hand control, representing a sensorimotor feedback efficiency index.

Robot-assisted image-guided transcranial magnetic stimulation for somatotopic mapping of the motor cortex: a clinical pilot study

PurposeShape and exact location of motor cortical areas varies among individuals. The exact knowledge of these locations is crucial for planning of neurosurgical procedures. In this study, we have used robot-assisted image-guided transcranial magnetic stimulation (Ri-TMS) to elicit MEP response recorded for individual muscles and reconstruct functional motor maps of the primary motor cortex.MethodsOne healthy volunteer and five patients with intracranial tumors neighboring the precentral gyrus were selected for this pilot study. Conventional MRI and fMRI were obtained. Transcranial magnetic stimulation was performed using a MagPro X100 stimulator and a standard figure-of-eight coil positioned by an Adept Viper s850 robot. The fMRI activation/Ri-TMS response pattern were compared. In two cases, Ri-TMS was additionally compared to intraoperative direct electrical cortical stimulation.ResultsMaximal MEP response of the m. abductor digiti minimi was located in an area corresponding to the “hand knob” of the precentral gyrus for both hemispheres. Repeated Ri-TMS measurements showed a high reproducibility. Simultaneous registration of the MEP response for m. brachioradialis, m. abductor pollicis brevis, and m. abductor digiti minimi demonstrated individual peak areas of maximal MEP response for the individual muscle groups. Ri-TMS mapping was compared to the corresponding fMRI studies. The areas of maximal MEP response localized within the “finger tapping” activated areas by fMRI in all six individuals.ConclusionsRi-TMS is suitable for high resolution non-invasive preoperative somatotopic mapping of the motor cortex. Ri-TMS may help in the planning of neurosurgical procedures and may be directly used in navigation systems.

A syndrome of the dentate nucleus mimicking psychogenic ataxia

To date, cerebellar involvement in control of non-motor functions like cognition and emotion is increasingly well established. Current models suggest that motor and non-motor networks connecting the cerebellum with cortical areas operate independently in closed and segregated loops. Here, we report a 59-year-old female patient with a small cerebellar lesion that shows that cognitive activation can significantly influence cerebellar motor control. Surprisingly, this led to a clinical picture mimicking a psychogenic disorder. Similar to non-human primates, this case suggests that the human dentate nucleus consists of distinct cognitive and motor domains with additional somatotopical arrangement of the latter. Extending current models of cerebro-cerebellar interaction, this case further illustrates that there can be significant functional cross-talk between motor and cognitive cerebellar networks.

3D mapping of somatotopic reorganization with small animal functional MRI

There are few in vivo noninvasive methods to study neuroplasticity in animal brains. Functional MRI (fMRI) has been developed for animal brain mapping, but few fMRI studies have analyzed functional alteration due to plasticity in animal models. One major limitation is that fMRI maps are characterized by statistical parametric mapping making the apparent boundary dependent on the statistical threshold used. Here, we developed a method to characterize the location of center-of-mass in fMRI maps that is shown not to be sensitive to statistical threshold. Utilizing centers-of-mass as anchor points to fit the spatial distribution of the BOLD response enabled quantitative group analysis of altered boundaries of functional somatosensory maps. This approach was used to study cortical reorganization in the rat primary somatosensory cortex (S1) after sensory deprivation to the barrel cortex by follicle ablation (F.A.). FMRI demonstrated an enlarged nose S1 representation in the 3D somatotopic functional maps. This result clearly demonstrates that fMRI enables the spatial mapping of functional changes that can characterize multiple regions of S1 cortex and still be sensitive to changes due to plasticity.

Learning cortical representations from multiple whisker inputs

Rats' whiskers convey tactile information to the somatosensory cortex, where layer 4 neurons are clustered into barrels, each responding primarily to input from one principal whisker (PW). The spatial arrangement of the barrels reflects the spatial arrangement of the whiskers on the animal's snout, thus representing the whiskers in a somatotopic map. Within a barrel, neurons are selective for the direction in which the PW is deflected, and across layer 2/3 directions may be organized into a pinwheel map such that deflection of whisker A towards whisker B activates barrel field A neurons located closest to barrel field B [1] (Figure 1c). More recently layer 5 neurons have been found to be selective for the direction in which waves of sequential deflections are applied across multiple whiskers, although the potential spatial organization of a map for these stimuli has not yet been determined [2].

A computational model for the excitatory network of the C2 column of barrel cortex

Many animals, especially rodents, use whiskers as an important sensory input. One of the multiple interesting properties of the whisker sensory pathway is its somatotopic mapping. Every single whisker has a local representation in the primary sensory cortex. In this barrel cortex, each whisker is represented by a single column of cortex. The excitatory connections of the C2 barrel cortex column were researched thoroughly in [1].

Optical imaging of digit topography in individual awake and anesthetized squirrel monkeys.

Topographic maps and columnar structures are fundamental to cortical sensory information processing. Most of the knowledge about detailed topographic maps and columnar structure comes mainly from experiments conducted on anesthetized animals. Towards the goal of evaluating whether topographic maps change with respect to behavioral demands, we used intrinsic signal optical imaging in alert monkeys to examine the spatial specificity of cortical topographic representation. Specifically, the somatotopies of neighboring distal finger pad representation in areas 3b and 1 were examined in the same awake and anesthetized squirrel monkey. In comparison to the anesthetized animal, we found larger cortical activation sizes in the alert animal in area 3b, where activation widths were found to overlap with even non-adjacent digits. This may suggest that in the alert animal, there is less inhibition across the somatotopic map within area 3b.

Topographical Organization of the Pyramidal Fiber System - Diffusion Tensor MRI of the Human and Rhesus Monkey Brain

The fibers of the pyramidal tract (PT) that connect the precentral and postcentral gyrus with the spinal cord are organized in a topological manner. However, their exact arrangement and orientation in the internal capsule is still a mat- ter of debate. Here, we applied magnetic resonance diffusion tensor imaging and tract tracing techniques to determine and compare the pyramidal fibers from the primary motor and somatosensory system in humans and rhesus monkeys in vivo. The results demonstrate that the pyramidal systems of the human and monkey brain differ in their orientation at the level of the internal capsule, whereas track orientations in the gyrus and brainstem appear similar. In the monkey internal cap- sule the somatotopic arrangement of PT fibers from the upper and lower extremities form an angle with the left-right axis of 146° ± 23° (n=4). Thus, fibers from lateral areas of the gyrus are located more anterior-medial to fibers from medial cortical areas. In contrast, in humans the angle is only 50° ± 16° (n=9) yielding a more anterior-lateral orientation of PT fibers along the short axis of the internal capsule. These species dependencies may possibly be due to structural con- straints of the smaller and differently shaped monkey brain.

Nocturnal orientation and object recognition through active electrolocation in weakly electric fish

Event Abstract Back to Event Nocturnal orientation and object recognition through active electrolocation in weakly electric fish Gerhard V. Emde1* 1 Universität Bonn, Institut für Zoologie, Germany Weakly electric fish orient at night by employing active electrolocation. The African mormyridae emit brief electric pulse-type signals and perceive the consequences of these emissions with more than 2500 epidermal electroreceptor organs, which are distributed over almost their entire skin surface. Electroreceptors project to three somatotopic maps in the lateral line lobe in the brainstem, where primary processing of electrosensory information takes place. Fish can detect and recognize nearby objects by analyzing the electric images, which objects project onto the animal's skin surface. Electric images depend on size, distance, shape, and material of objects and on the morphology of the electric organ and the fish’s body. Behavioural experiments have shown that the mormyrid Gnathonemus petersii can determine the resistive and capacitive components of an object's complex impedance in order to identify living prey items during foraging. In addition, fish can measure the distance and three-dimensional shape of objects. In order to perceive object properties during active electrolocation, the fish have to measure at least four parameters of the local signal within an object's electric image: peak amplitude, maximal slope, image width, and waveform distortions. Fish have certain behavioural strategies in order to optimize object recognition. It is proposed that G. petersii possesses two electroreceptive "foveae" at its elongated chin (Schnauzenorgan) and at its nasal region, both of which resemble the visual fovea in the retina of the eye in design, function and behavioural use. Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Oral Presentation Topic: Symposium 20 – Mormyrid fishes in myth, membranes and molecules Citation: Emde GV (2009). Nocturnal orientation and object recognition through active electrolocation in weakly electric fish. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.069 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 20 Nov 2009; Published Online: 20 Nov 2009. * Correspondence: Gerhard V Emde, Universität Bonn, Institut für Zoologie, Bonn, Germany, vonderemde@uni-bonn.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Gerhard V Emde Google Gerhard V Emde Google Scholar Gerhard V Emde PubMed Gerhard V Emde Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Cortically Evoked Long-Lasting Inhibition of Pallidal Neurons in a Transgenic Mouse Model of Dystonia

Dystonia is a neurological disorder characterized by sustained or repetitive involuntary muscle contractions and abnormal postures. To understand the pathophysiology of dystonia, neurophysiological analyses were performed on hyperkinetic transgenic mice generated as a model of DYT1 dystonia. Abnormal muscle activity, such as coactivation of agonist and antagonist muscles and sustained muscle activation, was frequently observed in these mice. Recording of neuronal activity in the awake state revealed reduced spontaneous activity with bursts and pauses in both the external and internal segments of the globus pallidus. Motor cortical stimulation evoked responses composed of excitation and subsequent long-lasting inhibition in both pallidal segments, which were never observed in the normal mice. In addition, the somatotopic arrangements in both pallidal segments were disorganized. Long-lasting inhibition induced by cortical inputs in the internal pallidal segment may disinhibit thalamic and cortical activity, resulting in the motor hyperactivity observed in the transgenic mice.

Excitation and Inhibition Jointly Regulate Cortical Reorganization in Adult Rats

The primary somatosensory cortex (SI) retains its capability for cortical reorganization after injury or differential use into adulthood. The plastic response of SI cells to peripheral stimulation is characterized by extension of cortical representations accompanied by changes of the receptive field size of neurons. We used intracortical microstimulation that is known to enforce local, intracortical synchronous activity, to induce cortical reorganization and applied immunohistochemical methods in the same individual animals to investigate how plasticity in the cortical topographic maps is linked to changes in the spatial layout of the inhibitory and excitatory neurotransmitter systems. The results reveal a differential spatiotemporal pattern of upregulation and downregulation of specific factors for an excitatory (glutamatergic) and an inhibitory (GABAergic) system, associated with changes of receptive field size and reorganization of the somatotopic map in the rat SI. Predominantly local mechanisms are the specific reduction of the calcium-binding protein parvalbumin in inhibitory neurons and the low expression of the activity marker c-Fos. Reorganization in the hindpaw representation and in the adjacent SI cortical areas (motor cortex and parietal cortex) is accompanied by a major increase of the excitatory transmitter glutamate and c-Fos. The spatial extent of the reorganization appears to be limited by an increase of glutamic acid decarboxylase and the inhibitory transmitter GABA. The local and medium-range net effects are excitatory and can facilitate receptive field enlargements and cortical map expansion. The longer-range increase of inhibition appears suited to limit these effects and to prevent neurons from pathological hyperexcitability.

Cerebral columnar organization of the first nociceptive component induced by CO2 laser on the tail of the rat

The somatotopic map of the first nociceptive component in the primary somatosensory cortex (S1) is still unclear. In this study, a CO2 laser was applied to the tail of the rat to induce nociception without the interference from large myelinated (Aβ) fibers. Thus, only noxious fibers could be activated. Two-dimensional current-source-density analysis was used to analyze the evoked field potentials. Using this method, the nociceptive responses of Aδ-fibers in S1 were verified, and the somatotopic map of the first nociceptive component in S1 was identified. We found that whether light touch or laser-induced nociception was applied to the tail of the rat, the responsive topography in S1 was consistent. Discrimination of these two modalities was achieved vertically in the same column; the deeper layer represented the nociceptive response while the superficial layer encoded the response to light touch. This is quite different from that of a primate brain.

Complex Organization of Human Primary Motor Cortex: A High-Resolution fMRI Study

A traditional view of the human motor cortex is that it contains an overlapping sequence of body part representations from the tongue in a ventral location to the foot in a dorsal location. In this study, high-resolution functional MRI (1.5x1.5x2 mm) was used to examine the somatotopic map in the lateral motor cortex of humans, to determine whether it followed the traditional somatotopic order or whether it contained any violations of that somatotopic order. The arm and hand representation had a complex organization in which the arm was relatively emphasized in two areas: one dorsal and the other ventral to a region that emphasized the fingers. This violation of a traditional somatotopic order suggests that the motor cortex is not merely a map of the body but is topographically shaped by other influences, perhaps including correlations in the use of body parts in the motor repertoire.

Thin-film epidural microelectrode arrays for somatosensory and motor cortex mapping in rat

Assessments of somatosensory and motor cortical somatotopy in vivo can provide important information on sensorimotor physiology. Here, novel polyimide-based thin-film microelectrode arrays (72 contacts) implanted epidurally, were used for recording of somatosensory evoked potentials (SEPs) and somatosensory cortex somatotopic maps of the rat. The objective was to evaluate this method with respect to precision and reliability. SEPs and somatosensory maps were measured twice within one session and again after 8 days of rest. Additionally, motor cortex maps were acquired once to assess the spatial relationship between somatosensory and motor representations of fore- and hindlimb within one individual. Somatosensory maps were well reproduced within and between sessions. SEP amplitudes and latencies were highly reliable within one recording session (combined intraclass correlation 90.5%), but less so between sessions (21.0%). Somatosensory map geometry was stable within and between sessions. For the forelimb the somatosensory representation had a 30% overlap with the corresponding motor area. No significant overlap was found for the hindlimb. No evidence for cortical injury was found on histology (Nissl). Thin-film epidural electrode array technology enables a detailed assessment of sensorimotor cortex physiology in vivo and can be used in longitudinal designs enabling studies of learning and plasticity processes.

A multiarray electrode mapping method for percutaneous thermocoagulation as treatment of trigeminal neuralgia. Technical note on a series of 178 consecutive procedures

Background We describe our method and mapping technique of the trigeminal nerve using a quadripolar electrode to minimize morbidity of percutaneous thermocoagulation as treatment of trigeminal neuralgia. Method Of 381 patients selected for postgasserian thermocoagulation, 178 consecutive procedures were carried out using, in most cases, our painless and ambulatory method and technique. All patients were preoperatively subjected to 3-dimensional constructive interference in steady-state magnetic resonance and magnetic resonance angiography. Transgasserian introduction of our quadripolar multiarray electrode under constant fluoroscopic monitoring is used with systematic recording of radiologic angles at, in front of, and behind the clivus profile, always below the selar floor. The individual's somatotopic map based on the verbal responses of 34 facial subsegments in lieu of the usual 3 is carefully established. Lesions are aimed at the trigger of pain and restricted to fibers with the lowest thresholds. Maximal lesions are one third the size used in conventional thermocoagulation. Lesions attempt to avoid damage to the first division, uninvolved fibers, and the motor division. Results Pre- and postoperatory thresholds demonstrate that trigger-aimed small lesions do not extend to unwanted subsegments. The described technique can minimize unnecessary complications from percutaneous thermocoagulation.

Western Medicine and Auriculotherapy: a comparative analysis of two paradigmatic approaches to the external ear

The external ear is an often overlooked structure that serves several important functions in humans and in other species. Western Medicine conceives of the external ear in terms of its function, embryology, innervation and clinical syndromes with auricular manifestations. Non‐western traditions, however, perceive the external ear in a way that challenges the paradigm accepted in Western Medicine. The purpose of this study was to assess the different approaches to auricular morphology and function, and to see whether or not there is something to be gained, in terms of Western Medicine's understanding of anatomy and function, by looking at non‐Western traditions. A review of Western and Chinese literature was conducted. Results show that a general understanding of the external ear in Chinese Medicine is based upon a “somatotopic map” (i.e., different regions of the auricle are believed to correspond to different areas of the body). This map provides the basis by which general medical conditions can be both diagnosed and treated using the modality known as “auriculotherapy” which includes, but is not limited to, auricular acupuncture. While this model appears to be outside of accepted Western Medical dogma, auriculotherapy is in fact closely related to such familiar entities as referred otalgia, as well as well‐documented, neurally‐mediated reflexes involving the external ear.

Experience‐dependent changes in spatiotemporal properties of cutaneous inputs remodel somatosensory cortical maps following skin flap rotation

Contiguous skin surfaces that tend to be synchronously stimulated are represented in neighbouring sectors of primary somatosensory maps. Moreover, neuronal receptive fields (RFs) are reshaped through ongoing competitive/cooperative interactions that segregate/desegregate inputs converging onto cortical neuronal targets. The present study was designed to evaluate the influence of spatio-temporal constraints on somatotopic map organization. A vascularized and innervated pedicle flap of the ventrum skin bearing nipples was rotated by 180 degrees . Electrophysiological maps of ventrum skin were elaborated in the same rats at 24 h after surgery and 2 weeks after parturition. Neurones with split RFs resulting from the surgical separation of formerly adjoining skin surfaces were more numerous in non-nursing than nursing rats. RFs that included newly adjacent skin surfaces on both sides of the scar line emerged in nursing rats, suggesting that the spatial contiguity of formerly separated skin surfaces induced a fusion of their cortical representations through nursing-induced stimulation. In addition, nursing-dependent inputs were found to reincorporate the rotated skin flap representation in an updated topographical organization of the cortical map. A skin territory including recipient and translocated skin areas was costimulated for 7 h, using a brushing device. Neural responses evoked by a piezoelectric-induced skin indentation before and after skin brushing confirmed the emergence of RFs crossing the scar line and contraction of non-brushed components of split RFs. Our findings provide further evidence that the spatiotemporal structure of sensory inputs changing rapidly or evolving in a natural context is critical for experience-dependent reorganization of cortical map topography.

Digit Somatotopy within Cortical Areas of the Postcentral Gyrus in Humans

Characterizing the cortical representation of the body surface is fundamental to understanding the neural basis of human somatic sensation. Monkey studies benefited from the detailed somatotopic maps obtained from electrophysiology methods. Advances in noninvasive neuroimaging techniques now permit such questions to be probed in humans. The present study characterizes the detailed somatotopic representation of individual digits within subregions of the postcentral gyrus in humans using high-spatial resolution functional magnetic resonance imaging and surface-based mapping. Four areas of consistent activation included area 3b, area 2, and 2 discrete foci within area 1. Area 3b and the superior area 1 foci demonstrated an orderly somatotopic distribution for all digits of the hand, whereby the thumb was represented most lateral, anterior, and inferior and the fifth digit was most medial, posterior, and superior. Compared with area 3b, somatotopic variability was greater in area 1 and the digits spanned less cortical territory. This study additionally identified the specific digit pairs that are separable in areas 3b and 1 using current imaging methods. Somatotopy was not resolved in area 2 or in the inferior area 1 foci.

Sorting food from stones: the vagal taste system in Goldfish, Carassius auratus

The sense of taste, although a relatively undistinguished sensory modality in most mammals, is a highly developed sense in many fishes, e.g., catfish, gadids, and carps including goldfish. In these species, the amount of neural tissue devoted to this modality may approach 20% of the entire brain mass, reflecting an enormous number of taste buds scattered across the external surface of the animal as well as within the oral cavity. The primary sensory nuclei for taste form a longitudinal column of nuclei along the dorsomedial surface of the medulla. Within this column of gustatory nuclei, the sensory system is represented as a fine-grain somatotopic map, with external body parts being represented rostrally within the column, and oropharyngeal surfaces being represented caudally. Goldfish have a specialization of the oral cavity, the palatal organ, which enables them to sort food particles from particulate substrate material such as gravel. The palatal organ taste information reaches the large, vagal lobe with a complex laminar and columnar organization. This lobe also supports a radially-organized reflex system which activates the musculature of the palatal organ to effect the sorting operation. The stereotyped, laminated structure of this system in goldfish has facilitated studies of the circuitry and neurotransmitter systems underlying the goldfish's ability to sort food from stones.

Organization of pERK‐immunoreactive cells in trigeminal spinal nucleus caudalis and upper cervical cord following capsaicin injection into oral and craniofacial regions in rats

To define the somatotopic arrangement of neurons in the trigeminal spinal subnucleus caudalis and upper cervical cord activated by acute noxious stimulation of various orofacial sites, pERK expression was analyzed in these neurons. After capsaicin injection into the tongue, lower gum, upper and lower lips, or mental region, pERK-like immunoreactive (pERK-LI) cells were distributed mainly in the dorsal half of the trigeminal spinal nucleus interporalis (Vi) and caudalis (Vc) transition zone (Vi/Vc zone), middle Vc, and Vc and upper cervical cord transition zone (Vc/C2 zone). pERK-LI cells were distributed throughout the dorsal to ventral portion of the Vi/Vc zone, middle Vc, and Vc/C2 zone following capsaicin injection into the anterior hard palate, upper gum, buccal mucosa, or vibrissal pad and in the ventral portion of the Vi/Vc zone, middle Vc, and Vc/C2 zone following snout, ophthalmic, or ocular injection of capsaicin. The rostrocaudal distribution area of pERK-LI cells was more extensive from the Vi/Vc zone to the Vc/C2 zone after intraoral injection than that after facial injection, and the rostrocaudal distribution of pERK-LI cells from the Vi/Vc zone to the Vc/C2 zone had a somatotopic arrangement, with the snout being represented most rostrally and ophthalmic, ocular, or mental regions represented most caudally. These findings suggest that the pERK-LI cells expressed from the Vi/Vc zone to the Vc/C2 zone following injection of capsaicin in facial and intraoral structures may be differentially involved in pain perception in facial and intraoral sites.