Figure 4 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
The motor-sensory homunculus redrawn. (A) The proportions of this first homunculus correspond to those of the original reproduced in Fig. 1. All other homunculi in B-D are derived from an average of the motor and somatosensory maps produced in Fig. 2 and Supplementary Fig. 1. (B) Homunculus generated from the surface maps. (C) Homunculus derived from the vertical length measurements. (D) Homunculus derived from the number of stimulation points. All measurements are from Penfield and Boldrey (1937).
Source publication
Eighty years ago, Penfield and Boldrey introduced the homunculus in a paper published in Brain. In a reappraisal of the iconic aide-mémoire, Marco Catani reanalyses the original data, and argues that through its extended network the homunculus holds the key to the precise coding that results in coordinated activation of peripheral muscles.
Context in source publication
Context 1
... tions of the homunculus started to appear in popular text- books, where its altered proportions were thought to reflect the extension of the area of each body part (Fig. 2B). To rectify this historical error, different versions of a modern motor-sensory homunculus have been generated using the data available in the original paper and presented in Fig. 4. A comparison of the different homunculi shows that the original version was not proportionally scaled accord- ing to the measures reported in the 1937 paper. For exam- ple, the size of the tongue was clearly exaggerated in the first homunculus, a misrepresentation that Penfield reme- died in a following publication (Penfield and ...
Citations
... The distal core is surrounded by a belt of cortex mediating distal and proximal forelimb movements, which in turn is surrounded by a belt of cortex on the central sulcus convexity mediating proximal (elbow and shoulder) movements. Third, epicortical stimulation of the human precentral gyrus shows a pattern of intermingled distal and proximal joint movements on the gyral surface (Catani, 2017;Penfield & Boldrey, 1937). ...
High‐resolution anterograde tracers and stereology were used to study the terminal organization of the corticospinal projection (CSP) from the rostral portion of the primary motor cortex (M1r) to spinal levels C5–T1. Most of this projection (90%) terminated contralaterally within laminae V–IX, with the densest distribution in lamina VII. Moderate bouton numbers occurred in laminae VI, VIII, and IX with few in lamina V. Within lamina VII, labeling occurred over the distal‐related dorsolateral subsectors and proximal‐related ventromedial subsectors. Within motoneuron lamina IX, most terminations occurred in the proximal‐related dorsomedial quadrant, followed by the distal‐related dorsolateral quadrant. Segmentally, the contralateral lamina VII CSP gradually declined from C5–T1 but was consistently distributed at C5–C7 in lamina IX. The ipsilateral CSP ended in axial‐related lamina VIII and adjacent ventromedial region of lamina VII. These findings demonstrate the M1r CSP influences distal and proximal/axial‐related spinal targets. Thus, the M1r CSP represents a transitional CSP, positioned between the caudal M1 (M1c) CSP, which is 98% contralateral and optimally organized to mediate distal upper extremity movements (Morecraft et al., 2013), and dorsolateral premotor (LPMCd) CSP being 79% contralateral and optimally organized to mediate proximal/axial movements (Morecraft et al., 2019). This distal to proximal CSP gradient corresponds to the clinical deficits accompanying caudal to rostral motor cortex injury. The lamina IX CSP is considered in the light of anatomical and neurophysiological evidence which suggests M1c gives rise to the major proportion of the cortico‐motoneuronal (CM) projection, while there is a limited M1r CM projection.
... The discrimination of the different movements is more precise as the body parts in the somatosensory map are relatively far apart. 6 In particular, the imagination/execution of the right or left hand movement mainly involves the areas of the primary motor cortex in the contralateral hemisphere and, in the same hemisphere, the imagination/execution of feet movements activates a different region of the motor cortex with respect to a hand movement. 37 By relying on spatial filtering, differences can be emphasized in the EEGs, and the imagined/executed movement can be decoded with good accuracy. ...
... The neural mechanism underlying the observed ipsilateral transfer of proprioceptive and motor learning is not fully elucidated. However, it is well known that neural representations of elbow and wrist are located closely to each other and partially overlap in the somatosensory and motor cortical areas [26,27], Moreover, the same motor cortical neurons may respond to loads experienced at the shoulder and the elbow during reaching [28]. It has been suggested that a certain amount of overlap in cortical representations aids the formation and control of functional muscle synergies [29]. ...
Background
Learning of a visuomotor task not only leads to changes in motor performance but also improves proprioceptive function of the trained joint/limb system. Such sensorimotor learning may show intra-joint transfer that is observable at a previously untrained degrees of freedom of the trained joint.
Objective
Here, we examined if and to what extent such learning transfers to neighboring joints of the same limb and whether such transfer is observable in the motor as well as in the proprioceptive domain. Documenting such intra-limb transfer of sensorimotor learning holds promise for the neurorehabilitation of an impaired joint by training the neighboring joints.
Methods
Using a robotic exoskeleton, 15 healthy young adults (18–35 years) underwent a visuomotor training that required them to make continuous, increasingly precise, small amplitude wrist movements. Wrist and elbow position sense just-noticeable‐difference (JND) thresholds and spatial movement accuracy error (MAE) at wrist and elbow in an untrained pointing task were assessed before and immediately after, as well as 24 h after training.
Results
First, all participants showed evidence of proprioceptive and motor learning in both trained and untrained joints. The mean JND threshold decreased significantly by 30% in trained wrist (M: 1.26° to 0.88°) and by 35% in untrained elbow (M: 1.96° to 1.28°). Second, mean MAE in untrained pointing task reduced by 20% in trained wrist and the untrained elbow. Third, after 24 h the gains in proprioceptive learning persisted at both joints, while transferred motor learning gains had decayed to such extent that they were no longer significant at the group level.
Conclusion
Our findings document that a one-time sensorimotor training induces rapid learning gains in proprioceptive acuity and untrained sensorimotor performance at the practiced joint. Importantly, these gains transfer almost fully to the neighboring, proximal joint/limb system.
... Наличие изменений K αа в отведениях F3/F4 при перемене положения тела возможно объяснить следующим образом. Отведения F3 и F4 приблизительно находятся над дорсолатеральной префронтальной корой, которая связана с пространственной обработкой афферентной информации, приходящей по ассоциативным волокнам из различных участков коры, в т. ч. и из задней теменной, последовательно моделирует план действий или готовность к действию, а также корректирует осанку [12,14,15]. Соответственно, при переходе тела в другое положение, особенно в такие «напряженные» положения, как сидя и антиортостатический наклон, эта зона коры головного мозга должна быть активной слева или справа (в зависимости от доминантного полушария) для регуляции положения тела в пространстве. ...
Hemispheric asymmetry has been intensively studied by psycho- and neurophysiology mostly using electroencephalography (EEG) and functional magnetic resonance imaging. However, there is little data available on the characteristics of bioelectrical and haemodynamic asymmetry of the human brain during postural changes. This pilot study introduces a combined technique of simultaneous recording of brain haemodynamic and bioelectric asymmetry in different body positions. The aim of the paper was to compare asymmetry coefficients in three different body positions and to establish cortex areas with the most active shift in blood flow and alpha power in response to postural changes. The research involved 12 healthy volunteers aged between 20 and 25 years (mean age 21.4 ± 1.5 years) evenly distributed by sex. Materials and methods. Bioelectric and haemodynamic activity of the brain was assessed by means of rheoencephalography and EEG, respectively. Rheographic index and spectral power of alpha waves were recorded in three body positions (sitting, supine and 45° head-down tilt), followed by the calculation of haemodynamic asymmetry (Khda) and alpha asymmetry (Kαa) coefficients. Results. Statistical analysis of Khda showed no sex differences or significant differences in this parameter between the body positions, which can be explained by direct effects of baroreflex and cerebrovascular autoregulation. Statistical comparison of Kαa of EEG signals from all electrode leads with each other and in each position demonstrated significant changes in Kαa of P3/P4, T5/T6 and F3/F4 pairs in male subjects. These findings can indicate that posterior parietal cortex of both hemispheres and left parietotemporal region, which play an important role in spatial perception, as well as dorsolateral prefrontal cortex, which participates in muscle tone regulation for posture correction, are actively involved in bioelectrical response to postural changes.
... Motor homunculus of the brain was first described by Wilder Penfield and Edwin Boldrey on 1 December 1937, illustrated in a 55-page article entitled Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation [7]. The illustrated map indicated the special localization and area of the motor and somatosensory cortex of each part of the body; however, it was declared that the noted areas of each part of the body show overlapped areas [8]. ...
... It receives direct inputs from the postcentral somatosensory cortex, developing a mechanism of crosstalk between the two regions, in which the connection is elaborated through U-shaped fibers [9]. This coordination between these pre-and postcentral regions is showed to be necessary for learning and doing some actions which need fine motor movements [8]. ...
Background:
Several etiologies are responsible for presentation of a twitching tongue in clinical practice. Some of these etiologies cause an isolated hyperkinetic tongue muscle, and some others cause it along with other signs and symptoms.
Objectives:
The present paper aims to review the causes, pathology, and presentations reported with twitchy tongue. An anatomical basis of the etiologies responsible for presentation of a twitchy tongue and hyperkinetic movement disorders of this muscle is pursued.
Method:
The reporting of this systematic review was guided by the standards of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) Statement. All of the research papers conducted with keywords described in the method section between 2000 and 2022 were used, and review articles and articles without any human subject and without any described hyperkinetic movement disorders of the tongue were excluded.
Results:
All of the etiologies responsible for hyperkinetic movement disorders of tongue were listed in the basis of their anatomical site of effect; cortical region, basal ganglia, cerebellum, brain stem, nucleus and nerve, and neuromuscular junction. One last remained part is the "not classified" section, which contains the etiologies with no particular anatomical origin.
Conclusion:
There are a variety of responsible etiologies for presentation of a twitchy tongue, and in the matter of a complaint of hyperkinetic tongue presentation, physicians should consider anatomical, functional, and psychological etiologies and other signs and symptoms must be participated in the diagnosis process to achieve a proper medical decision.
... Ltd., Tokyo, Japan) were compared with the Penfield's homunculus on cerebral cartography (Catani, 2017;Schott, 1993). After automatically calculating the precentral gyrus SUVs in slices 6-30 (identified by the software as the slices containing the primary motor cortex), these slices were divided into four equal parts (slice numbers 7-12; slice numbers 13-18; slice numbers 19-24; slice numbers 25-30). ...
Confirmation of the exact voluntary movements of patients with disorder of consciousness following severe traumatic brain injury (TBI) is difficult because of the associated communication disturbances. In this pilot study, we investigated whether regional brain glucose metabolism assessed by 18 F-fluorodeoxyglucose positron emission tomography (FDG-PET) at rest could predict voluntary movement in severe TBI patients, particularly those with sufficient upper limb capacity to use communication devices. We visually and verbally instructed patients to clasp or open their hands. After video capture, three independent rehabilitation therapists determined whether the patients' movements were voluntary or involuntary. The results were compared with the standardized uptake value in the primary motor cortex, referring to the Penfield's homunculus, by resting state by FDG-PET imaged 1 year prior. Results showed that glucose uptake in the left (p = 0.0015) and right (p = 0.0121) proximal limb of the primary motor cortex, based on Penfield's homunculus on cerebral cartography, may reflect contralateral voluntary movement. Receiver operating characteristic curve analysis showed that a mean cutoff standardized uptake value of 5.47 ± 0.08 provided the best sensitivity and specificity for differentiating between voluntary and involuntary movements in each area. FDG-PET may be a useful and robust biomarker for predicting long-term recovery of motor function in severe TBI patients with disorders of consciousness.
... Interestingly, such segregation is consistent with previous data gained via functional and structural imaging of the precentral gyrus, which showed a dorso-ventral gradient of four components, each one being responsible of different aspects of hand and upper limb control [59]. These findings challenge the classical view of the motor homunculus, in favor of a more action driven organization, or ethological map of action [15,60,61]. Even if NMR can be elicited on the medial wall of the hemisphere, no precise areas have yet been identified [53]. ...
Improving the onco-functional balance has always been a challenge in glioma surgery, especially regarding motor function. Given the importance of conation (i.e., the willingness which leads to action) in patient’s quality of life, we propose here to review the evolution of its intraoperative assessment through a reminder of the increasing knowledge of its neural foundations—based upon a meta-networking organization at three levels. Historical preservation of the primary motor cortex and pyramidal pathway (first level), which was mostly dedicated to avoid hemiplegia, has nonetheless shown its limits to prevent the occurrence of long-term deficits regarding complex movement. Then, preservation of the movement control network (second level) has permitted to prevent such more subtle (but possibly disabling) deficits thanks to intraoperative mapping with direct electrostimulations in awake conditions. Finally, integrating movement control in a multitasking evaluation during awake surgery (third level) enabled to preserve movement volition in its highest and finest level according to patients’ specific demands (e.g., to play instrument or to perform sports). Understanding these three levels of conation and its underlying cortico-subcortical neural basis is therefore critical to propose an individualized surgical strategy centered on patient’s choice: this implies an increasingly use of awake mapping and cognitive monitoring regardless of the involved hemisphere. Moreover, this also pleads for a finer and systematic assessment of conation before, during and after glioma surgery as well as for a stronger integration of fundamental neurosciences into clinical practice.
... cortex [16]. To take the most from the spatial localization of EEG activity related to movement imagination, spatial filtering can be of great help and some methods were proposed in the literature, CSP is one of the most powerful and popular ones [4]. ...
The present paper introduces a novel method, named AutoEncoder-Filter Bank Common Spatial Patterns (AE-FBCSP), to decode imagined movements from electroencephalography (EEG). AE-FBCSP is an extension of the well-established FBCSP and is based on a global (cross-subject) and subsequent transfer learning subject-specific (intra-subject) approach. A multi-way extension of AE-FBCSP is also introduced in this paper. Features are extracted from high-density EEG (64 electrodes), by means of FBCSP, and used to train a custom AE, in an unsupervised way, to project the features into a compressed latent space. Latent features are used to train a supervised classifier (feed forward neural network) to decode the imagined movement. The proposed method was tested using a public dataset of EEGs collected from 109 subjects. The dataset consists of right-hand, left-hand, both hands, both feet motor imagery and resting EEGs. AE-FBCSP was extensively tested in the 3-way classification (right hand vs left hand vs resting) and also in the 2-way, 4-way and 5-way ones, both in cross- and intra-subject analysis. AE-FBCSP outperformed standard FBCSP in a statistically significant way (p > 0.05) and achieved a subject-specific average accuracy of 89.09% in the 3-way classification. The proposed methodology performed subject-specific classification better than other comparable methods in the literature, applied to the same dataset, also in the 2-way, 4-way and 5-way tasks. One of the most interesting outcomes is that AE-FBCSP remarkably increased the number of subjects that responded with a very high accuracy, which is a fundamental requirement for BCI systems to be applied in practice.
... But even if we restrict our attention to the motor functions of the CST, it is hard to come up with a good argument in favour of strict somatotopy. There is now wealth of evidence in both humans and non-human primates that M1, for example, is not organized along the lines of a detailed 'homunculus' [49][50][51] or 'simunculus', 52-55 respectively. In M1, the evidence instead suggests that particular muscles and movements have multiple representations which overlap heavily with those of other muscles and movements. ...
We review the spatial organisation of corticospinal outputs from different cortical areas and how this reflects the varied functions mediated by the corticospinal tract. A long-standing question is whether the primate corticospinal tract shows somatotopical organisation. Although this has been clearly demonstrated for corticofugal outputs passing through the internal capsule and cerebral peduncle, there is accumulating evidence against somatotopy in the pyramidal tract in the lower brainstem and in the spinal course of the corticospinal tract. Answering the question on somatotopy has important consequences for understanding the effects of incomplete spinal cord injury.
Our recent study in the macaque monkey, using high-resolution dextran tracers, demonstrated a great deal of intermingling of fibres originating from primary motor cortex arm/hand, shoulder and leg areas. We quantified the distribution of fibres belonging to these different projections, and showed no significant difference in their distribution across different subsectors of the pyramidal tract or lateral corticospinal tract, arguing against somatotopy. We further demonstrated intermingling with corticospinal outputs derived from premotor and supplementary motor areas upper limb areas.
We present new evidence against somatotopy from corticospinal projections from rostral and caudal cingulate motor areas and from somatosensory areas of the parietal cortex. In the pyramidal tract and lateral corticospinal tract fibres from the cingulate motor areas overlap with each other. Fibres from primary somatosensory cortex arm area completely overlap those from the leg area. There is also substantial overlap of both these outputs with those from posterior parietal sensorimotor areas.
We argue that the extensive intermingling of corticospinal outputs from so many different cortical regions must represent an organisational principle, closely related to its mediation of many different functions and its large range of fibre diameters.
The motor sequelae of incomplete spinal injury, such as Central Cord Syndrome and ‘cruciate paralysis’, include much greater deficits in upper than in lower limb movement. Current teaching and text book explanations of these symptoms are still based on a supposed corticospinal somatotopy or ‘lamination’, with greater vulnerability of arm and hand vs leg fibres. We suggest that such explanations should now be finally abandoned. Instead, the clinical and neurobiological implications of the complex organisation of the corticospinal tract need now to be taken into consideration. This leads us to consider the evidence for a greater relative influence of the corticospinal tract on upper vs lower limb movements, the latter best characterised by skilled hand and digit movements.
... The neural mechanism underlying the observed ipsilateral transfer of proprioceptive and motor learning is not fully elucidated. However, it is well known that neural representations of elbow and wrist are located closely to each other and partially overlap in the somatosensory and motor cortical areas (25,26), Moreover, the same motor cortical neurons may respond to loads experienced at the shoulder and the elbow during reaching (27). It has been suggested that a certain amount of overlap in cortical representations aids the formation and control of functional muscle synergies (28). ...
Background
Learning of a visuomotor task not only leads to changes in motor performance but also improves proprioceptive function of the trained joint/limb system. Such sensorimotor learning may show intra-joint transfer that is observable at a previously untrained degrees of freedom of the trained joint. In addition, it may transfer to the homologous joint of contralateral side.
Objective
Here, we examined if and to what extent such learning transfers to neighboring joints of the same limb and whether such transfer is observable in the motor as well as in the proprioceptive domain. Documenting such intra-limb transfer of sensorimotor learning holds promise for the neurorehabilitation of an impaired joint by training the neighboring joints.
Methods
Using a robotic exoskeleton, 15 healthy young adults (18–35 years) underwent a visuomotor training that required them to make continuous, increasingly precise, small amplitude wrist movements. Wrist and elbow position sense just-noticeable‐difference (JND) thresholds and spatial movement accuracy error (MAE) at wrist and elbow in an untrained pointing task were assessed before and immediately after, as well as 24 hours after training.
Results
First, all participants showed evidence of proprioceptive and motor learning in both trained and untrained joints. The mean JND threshold decreased significantly by 30% in trained wrist (M: 1.26° to 0.88°) and by 35% in untrained elbow (M: 1.96° to 1.28°). Second, mean MAE in untrained pointing task reduced by 20% in trained wrist and the untrained elbow. Third, after 24 hours the gains in proprioceptive learning persisted at both joint, while motor learning gains had decayed to such extent that they were no longer significant at the group level.
Conclusion
Our findings document that a one-time sensorimotor training induces rapid learning gains in proprioceptive acuity and untrained motor performance at the practiced joint. Importantly, these gains transfer almost fully to the neighboring, proximal joint/limb system.
