Beyond language: The unspoken sensory-motor representation of the tongue in non-primates, non-human and human primates

The English idiom “on the tip of my tongue” commonly acknowledges that something is known, but it cannot be immediately brought to mind. This phrase accurately describes sensorimotor functions of the tongue, which are fundamental for many tongue-related behaviors (e.g., speech), but often neglected by scientific research. Here, we review a wide range of studies conducted on non-primates, non-human and human primates with the aim of providing a comprehensive description of the cortical representation of the tongue's somatosensory inputs and motor outputs across different phylogenetic domains. First, we summarize how the properties of passive non-noxious mechanical stimuli are encoded in the putative somatosensory tongue area, which has a conserved location in the ventral portion of the somatosensory cortex across mammals. Second, we review how complex self-generated actions involving the tongue are represented in more anterior regions of the putative somato-motor tongue area. Finally, we describe multisensory response properties of the primate and non-primate tongue area by also defining how the cytoarchitecture of this area is affected by experience and deafferentation

Sensorimotor experience in virtual environments

The goal of rehabilitation is to reduce impairment and provide functional improvements resulting in quality participation in activities of life, Plasticity and motor learning principles provide inspiration for therapeutic interventions including movement repetition in a virtual reality environment, The objective of this research work was to investigate functional specific measurements (kinematic, behavioral) and neural correlates of motor experience of hand gesture activities in virtual environments stimulating sensory experience (VE) using a hand agent model. The fMRI compatible Virtual Environment Sign Language Instruction (VESLI) System was designed and developed to provide a number of rehabilitation and measurement features, to identify optimal learning conditions for individuals and to track changes in performance over time. Therapies and measurements incorporated into VESLI target and track specific impairments underlying dysfunction. The goal of improved measurement is to develop targeted interventions embedded in higher level tasks and to accurately track specific gains to understand the responses to treatment, and the impact the response may have upon higher level function such as participation in life. To further clarify the biological model of motor experiences and to understand the added value and role of virtual sensory stimulation and feedback which includes seeing one\u27s own hand movement, functional brain mapping was conducted with simultaneous kinematic analysis in healthy controls and in stroke subjects. It is believed that through the understanding of these neural activations, rehabilitation strategies advantaging the principles of plasticity and motor learning will become possible. The present research assessed successful practice conditions promoting gesture learning behavior in the individual. For the first time, functional imaging experiments mapped neural correlates of human interactions with complex virtual reality hands avatars moving synchronously with the subject\u27s own hands, Findings indicate that healthy control subjects learned intransitive gestures in virtual environments using the first and third person avatars, picture and text definitions, and while viewing visual feedback of their own hands, virtual hands avatars, and in the control condition, hidden hands. Moreover, exercise in a virtual environment with a first person avatar of hands recruited insular cortex activation over time, which might indicate that this activation has been associated with a sense of agency. Sensory augmentation in virtual environments modulated activations of important brain regions associated with action observation and action execution. Quality of the visual feedback was modulated and brain areas were identified where the amount of brain activation was positively or negatively correlated with the visual feedback, When subjects moved the right hand and saw unexpected response, the left virtual avatar hand moved, neural activation increased in the motor cortex ipsilateral to the moving hand This visual modulation might provide a helpful rehabilitation therapy for people with paralysis of the limb through visual augmentation of skills. A model was developed to study the effects of sensorimotor experience in virtual environments, and findings of the effect of sensorimotor experience in virtual environments upon brain activity and related behavioral measures. The research model represents a significant contribution to neuroscience research, and translational engineering practice, A model of neural activations correlated with kinematics and behavior can profoundly influence the delivery of rehabilitative services in the coming years by giving clinicians a framework for engaging patients in a sensorimotor environment that can optimally facilitate neural reorganization

The interaction between human vision and eye movements in health and disease

Human motor behaviour depends on the successful integration of vision and eye movements. Many studies have investigated neural correlates of visual processing in humans, but typically with the eyes stationary and fixated centrally. Similarly, many studies have sought to characterise which brain areas are responsible for oculomotor control, but generally in the absence of visual stimulation. The few studies to explicitly study the interaction between visual perception and eye movements suggest strong influences of both static and dynamic eye position on visual processing and modulation of oculomotor structures by properties of visual stimuli. However, the neural mechanisms underlying these interactions are poorly understood. This thesis uses a range of fMRI methodologies such as retinotopic mapping, multivariate analsyis techniques, dynamic causal modelling and ultra high resolution imaging to examine the interactions between the oculomotor and visual systems in the normal human brain. The results of the experiments presented in this thesis demonstrate that oculomotor behaviour has complex effects on activity in visual areas, while spatial properites of visual stimuli modify activity in oculomotor areas. Specifically, responses in the lateral geniculate nucleus and early cortical visual areas are modulated by saccadic eye movements (a process potentially mediated by the frontal eye fields) and by changes in static eye position. Additionally, responses in oculomotor structures such as the superior colliculus are biased for visual stimuli presented in the temporal rather than nasal hemifield. These findings reveal that although the visual and oculomotor systems are spatially segregated in the brain, they show a high degree of integration at the neural level. This is consistent with our everyday experience of the visual world where frequent eye movements do not lead to disruption of visual continuity and visual information is seamlessly transformed into motor behaviour

Complex Movements for Voluntary Actions Evoked by Electrical Stimulation in the Motor Cortex of Rats

Electrical intracortical microstimulation (ICMS) has been widely used to study the functional organization of the motor cortex. The ICMS with longer stimulus trains of about 500 ms (long-duration ICMS) evoked complex and coordinated movement, similar to those of natural behaviour. A recent paper (Ramanathan et al., 2006) have reported that long-duration ICMS in rat motor cortex can result in complex, multijoint forelimb movements organized in a roughly topography. We pose the question if different features of motor control (e.g. body map, movement patterns, target location in space) can develop overlapping maps in the forelimb region of the rat’s M1. We performed long-duration ICMS to evoke complex, multijoint forelimb movements and we used 3D motion analysis tools to measure kinematic variables of electrically-evoked movements. The analysis was aimed to define the classes of movement and their topography across the cortical surface. Then, the following kinematic parameters, related to the limb and the paw component, were determined from the analysis: maximal displacement in XYZ, latency, duration, peak velocity, mean velocity, number of peak velocity , trajectory, vector, path index. According to our methode, the repertoire of the limb movement included: abduction, adduction, extension, retraction and elevation while paw movements included: opening, closure, opening/closure sequence and supination. To analyze our data, multivariate test for difference in means (MANOVA), one-way ANOVA and Tukey’s test were performed

Investigating the cortical oscillatory correlates of smooth pursuit eye movements : a magnetoencephalographic study

Models of motion perception propose that eye movement estimates are integrated into middle temporal cortex (MT+) as a mechanism that disambiguates world motion from retinal motion induced by ego movement. Little is known about the relationship between eye movement signals in this area and cortical oscillations, a phenomenon linked to perceptual and motor processing. Magnetoencephalography was used to examine the significance of oscillations in this area during pursuit. Results from Experiment 1 suggest low-frequency suppression in MT+ reflects eye position during sinusoidal tracking. A control study (Experiment 2) examining activity in response to retinal slip suggests this was not due to pursuit error when the stimulus changed direction. Experiment 3 examined oscillations during pursuit at various head-centred eye eccentricities. No difference was found in the magnitude of activity as a function of eye position during pursuit, suggesting modulations in these rhythms was related to another aspect of the eye movement. Experiment 4 found no specific effects of eye velocity on alpha or beta, but there was a consistent effect of eye speed on beta activity. Additionally, there was no such effect found between alpha and eye speed, suggesting some functional distinction in the role of these rhythms in pursuit behaviour. In Chapter 4, two experiments examined cortical changes during pursuit (Experiment 5) and retinal motion adaptation (Experiment 6), and the subsequent motion aftereffect. Beta suppression in MT+ during oculomotor adaptation was a significant predictor of the motion aftereffect duration, perhaps indicating that beta changes index the efficacy with which the visual motion system is able to recalibrate itself in the presence of a stationary stimulus following adaptation. Taken together, these results suggest a role for beta suppression in MT+ during pursuit, which seems to reflect the processing of extraretinal signals for oculomotor control and the estimation of head-centred motion.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Investigating the cortical oscillatory correlates of smooth pursuit eye movements: a magnetoencephalographic study

Models of motion perception propose that eye movement estimates are integrated into middle temporal cortex (MT+) as a mechanism that disambiguates world motion from retinal motion induced by ego movement. Little is known about the relationship between eye movement signals in this area and cortical oscillations, a phenomenon linked to perceptual and motor processing. Magnetoencephalography was used to examine the significance of oscillations in this area during pursuit. Results from Experiment 1 suggest low-frequency suppression in MT+ reflects eye position during sinusoidal tracking. A control study (Experiment 2) examining activity in response to retinal slip suggests this was not due to pursuit error when the stimulus changed direction. Experiment 3 examined oscillations during pursuit at various head-centred eye eccentricities. No difference was found in the magnitude of activity as a function of eye position during pursuit, suggesting modulations in these rhythms was related to another aspect of the eye movement. Experiment 4 found no specific effects of eye velocity on alpha or beta, but there was a consistent effect of eye speed on beta activity. Additionally, there was no such effect found between alpha and eye speed, suggesting some functional distinction in the role of these rhythms in pursuit behaviour. In Chapter 4, two experiments examined cortical changes during pursuit (Experiment 5) and retinal motion adaptation (Experiment 6), and the subsequent motion aftereffect. Beta suppression in MT+ during oculomotor adaptation was a significant predictor of the motion aftereffect duration, perhaps indicating that beta changes index the efficacy with which the visual motion system is able to recalibrate itself in the presence of a stationary stimulus following adaptation. Taken together, these results suggest a role for beta suppression in MT+ during pursuit, which seems to reflect the processing of extraretinal signals for oculomotor control and the estimation of head-centred motion

Adults imitate to send a social signal

Humans are prolific imitators, even when copying may not be efficient. A variety of explanations have been advanced for this phenomenon, including that it is a side-effect of learning, that it arises from a lack of understanding of causality, to imitation being a mechanism to boost affiliation. This thesis systematically outlines the hypothesis that imitation is a social signal sent between interacting partners, which rests on testing whether our propensity to imitate is modulated by the social availability of the interaction partner (i.e., whether our interaction partner is watching us or not). I developed a dyadic block-moving paradigm that allowed us to test this hypothesis in a naturalistic manner in four behavioural and neuroimaging studies using functional near-infrared spectroscopy (fNIRS). I found that imitative fidelity was modulated by whether the interaction partner was watching the participant make their move or not, and this effect replicated across all four studies, in both neurotypicals and autistic participants. I also examined the neural correlates of responding to irrational actions, and of being watched. I found that being watched led to a robust deactivation in the right parietal cortex across both neurotypicals (in two studies) and autistic participants (one study). Among autistic participants we also found strong engagement in the left superior temporal sulcus (STS) when being watched. For responding to irrational actions, in one study of neurotypicals we found greater deactivation in the right superior parietal lobule (SPL) when making more irrational responses. In another study of autistic and neurotypical participants we found deactivation in the bilateral inferior parietal cortex (IPL) in neurotypicals when responding to irrational actions, while this deactivation appeared confined to the left IPL for autistic participants. Autistic participants also showed differentially higher engagement in the left occipitotemporal regions when responding to irrational actions. This thesis supports the social-signalling hypothesis of imitation and is accompanied by suggestions for future directions to explore this theory in more detail

Sensorimotor Modulations by Cognitive Processes During Accurate Speech Discrimination: An EEG Investigation of Dorsal Stream Processing

Internal models mediate the transmission of information between anterior and posterior regions of the dorsal stream in support of speech perception, though it remains unclear how this mechanism responds to cognitive processes in service of task demands. The purpose of the current study was to identify the influences of attention and working memory on sensorimotor activity across the dorsal stream during speech discrimination, with set size and signal clarity employed to modulate stimulus predictability and the time course of increased task demands, respectively. Independent Component Analysis of 64–channel EEG data identified bilateral sensorimotor mu and auditory alpha components from a cohort of 42 participants, indexing activity from anterior (mu) and posterior (auditory) aspects of the dorsal stream. Time frequency (ERSP) analysis evaluated task-related changes in focal activation patterns with phase coherence measures employed to track patterns of information flow across the dorsal stream. ERSP decomposition of mu clusters revealed event-related desynchronization (ERD) in beta and alpha bands, which were interpreted as evidence of forward (beta) and inverse (alpha) internal modeling across the time course of perception events. Stronger pre-stimulus mu alpha ERD in small set discrimination tasks was interpreted as more efficient attentional allocation due to the reduced sensory search space enabled by predictable stimuli. Mu-alpha and mu-beta ERD in peri- and post-stimulus periods were interpreted within the framework of Analysis by Synthesis as evidence of working memory activity for stimulus processing and maintenance, with weaker activity in degraded conditions suggesting that covert rehearsal mechanisms are sensitive to the quality of the stimulus being retained in working memory. Similar ERSP patterns across conditions despite the differences in stimulus predictability and clarity, suggest that subjects may have adapted to tasks. In light of this, future studies of sensorimotor processing should consider the ecological validity of the tasks employed, as well as the larger cognitive environment in which tasks are performed. The absence of interpretable patterns of mu-auditory coherence modulation across the time course of speech discrimination highlights the need for more sensitive analyses to probe dorsal stream connectivity

Clinical measures of the neurophysiological mechanisms of rehabilitation-induced improvements in chronic stroke

Stroke is a leading cause of disability with up to 83% of survivors suffering persistent hemiparesis. The only means to improve motor-function in the post-acute phase is with rehabilitation. The first study of this thesis investigated changes in proprioception at the elbow and wrist in comparison to healthy age- and sex-matched people. Differences in the magnitude and direction of perception varied with joint and motor-function status. This study emphasises the specificity of proprioception deficits and the need for quantitative testing for this input to motor control that may be independent of the reduced descending drive from the lesioned hemisphere. The subsequent studies investigated the physiological mechanisms of post-stroke recovery during Wii-based Movement Therapy (WMT) using wireless telemetry to record joint goniometry, lower-limb muscle activation and heart rate. Joint kinematics measured during therapy is the most direct measure of movement ability. Faster acceleration and peak deceleration reflected better movement control. Kinematic data were correlated with functional assessments measured pre- and post-therapy but not with active or passive range-of-motion, suggesting that range-of-motion is not a good test of functional improvements in chronic stroke. Lower-limb muscle activation was recorded bilaterally from tibialis anterior. Muscle symmetry and peak activation improved differently both within and between patients and WMT activities, and these correlated with improvements in lower-limb functional assessments. Finally, a post-hoc comparison between the cardiovascular responses with WMT and modified Constraint-Induced Movement Therapy (mCIMT) revealed a significant increase in peak heart rate and faster heart rate recovery time by late-therapy for WMT indicating increased cardiovascular fitness. Peak heart rate was always higher and heart rate recovery faster during mCIMT but neither changed by late-therapy, suggesting a sympathetic stress response to mCIMT activities that emphasise movement speed and high repetition rates. This thesis highlights the need for sensitive quantitative measures of post-stroke function. It is the first to report functional progress during an upper-limb therapy program. Finally, the results show that the functional capacity to improve post-stroke can be extended into the chronic period and that a targeted upper-limb protocol such as WMT can be multifactorial with ancillary lower-limb and cardiovascular benefits