Somatosensory Activity Research Articles

Reduced somatosensory activations in swallowing with age.

Understanding the neural functional organization of swallowing in healthy elders is essential in diagnosing and treating older adults with swallowing difficulties. The primary aims of this investigation were to identify the neural activation sites of different components of deglutition in healthy elders using functional Magnetic Resonance Imaging (fMRI) and to investigate age differences in the neural control of swallowing. Ten young (age range 19-25 years of age) and nine older (age range 66-77 years of age) right-handed healthy individuals were scanned in a 3-Tesla MRI scanner. Subjects were visually cued for both a "Swallow" task and for component/control tasks ("Prepare to swallow," "Tap your tongue," and "Clear your throat"). Behavioral interleaved gradient (BIG) methodology was used to address movement related artifacts. Between-group comparisons revealed statistically stronger activations in the primary somatosensory cortex of young adults during the motor tasks examined. Both groups showed activations in the major motor areas involved in the initiation and execution of movement; however, areas involved in sensory processing, sensorimotor integration and/or motor coordination and control, showed reduced or limited activity in the elderly. Potential implications of these findings for clinical practice are discussed.

Coordination of Hand Shape

The neural control of hand movement involves coordination of the sensory, motor, and memory systems. Recent studies have documented the motor coordinates for hand shape, but less is known about the corresponding patterns of somatosensory activity. To initiate this line of investigation, the present study characterized the sense of hand shape by evaluating the influence of differences in the amount of grasping or twisting force, and differences in forearm orientation. Human subjects were asked to use the left hand to report the perceived shape of the right hand. In the first experiment, six commonly grasped items were arranged on the table in front of the subject: bottle, doorknob, egg, notebook, carton, and pan. With eyes closed, subjects used the right hand to lightly touch, forcefully support, or imagine holding each object, while 15 joint angles were measured in each hand with a pair of wired gloves. The forces introduced by supporting or twisting did not influence the perceptual report of hand shape, but for most objects, the report was distorted in a consistent manner by differences in forearm orientation. Subjects appeared to adjust the intrinsic joint angles of the left hand, as well as the left wrist posture, so as to maintain the imagined object in its proper spatial orientation. In a second experiment, this result was largely replicated with unfamiliar objects. Thus, somatosensory and motor information appear to be coordinated in an object-based, spatial-coordinate system, sensitive to orientation relative to gravitational forces, but invariant to grasp forcefulness.

Meta-analytic evidence for common and distinct neural networks associated with directly experienced pain and empathy for pain

A growing body of evidence suggests that empathy for pain is underpinned by neural structures that are also involved in the direct experience of pain. In order to assess the consistency of this finding, an image-based meta-analysis of nine independent functional magnetic resonance imaging (fMRI) investigations and a coordinate-based meta-analysis of 32 studies that had investigated empathy for pain using fMRI were conducted. The results indicate that a core network consisting of bilateral anterior insular cortex and medial/anterior cingulate cortex is associated with empathy for pain. Activation in these areas overlaps with activation during directly experienced pain, and we link their involvement to representing global feeling states and the guidance of adaptive behavior for both self- and other-related experiences. Moreover, the image-based analysis demonstrates that depending on the type of experimental paradigm this core network was co-activated with distinct brain regions: While viewing pictures of body parts in painful situations recruited areas underpinning action understanding (inferior parietal/ventral premotor cortices) to a stronger extent, eliciting empathy by means of abstract visual information about the other's affective state more strongly engaged areas associated with inferring and representing mental states of self and other (precuneus, ventral medial prefrontal cortex, superior temporal cortex, and temporo-parietal junction). In addition, only the picture-based paradigms activated somatosensory areas, indicating that previous discrepancies concerning somatosensory activity during empathy for pain might have resulted from differences in experimental paradigms. We conclude that social neuroscience paradigms provide reliable and accurate insights into complex social phenomena such as empathy and that meta-analyses of previous studies are a valuable tool in this endeavor.

Interactions between adenosine and K+channel-related pathways in the coupling of somatosensory activation and pial arteriolar dilation

Multiple, perhaps interactive, mechanisms participate in the linkage between increased neural activity and cerebral vasodilation. In the present study, we assessed whether neural activation-related pial arteriolar dilation (PAD) involved interactions among adenosine (Ado) A(2) receptors (A(2)Rs), large-conductance Ca(2+)-operated K(+) (BK(Ca)) channels, and inward rectifier K(+) (K(ir)) channels. In rats with closed cranial windows, we monitored sciatic nerve stimulation (SNS)-induced PAD in the absence or presence of pharmacological blockade of A(2)Rs (ZM-241385), ecto-5'-nucleotidase (α,β-methylene-adenosine diphosphate), BK(Ca) channels (paxilline), and K(ir) channels (BaCl(2)). Individually, these interventions led to 53-66% reductions in SNS-induced PADs. Combined applications of these blockers led to little or no further repression of SNS-induced PADs, suggesting interactions among A(2)Rs and K(+) channels. In the absence of SNS, BaCl(2) blockade of K(ir) channels produced 52-80% reductions in Ado and NS-1619 (BK(Ca) channel activator)-induced PADs. In contrast, paxilline blockade of BK(Ca) channels was without effect on dilations elicited by KCl (K(ir) channel activator) and Ado suffusions, indicating that Ado- and NS-1619-associated PADs involved K(ir) channels. In addition, targeted ablation of the superficial glia limitans was associated with a selective 60-80% loss of NS-1619 responses, suggesting that the BK(Ca) channel participation (and paxilline sensitivity) derived largely from channels within the glia limitans. Additionally, blockade of either PKA or adenylyl cyclase caused markedly attenuated pial arteriolar responses to SNS and, in the absence of SNS, responses to Ado, KCl, and NS-1619. These findings suggested a key, possibly permissive, role for A(2)R-linked cAMP generation and PKA-induced K(+) channel phosphorylation in somatosensory activation-evoked PAD.

Attenuation of beta and gamma oscillations in schizophrenia spectrum patients following hand posture perturbation

Several electroencephalographic (EEG) studies in schizophrenia report that the patients have reduced evoked gamma activity following visual and auditory stimulation. Somatosensory gamma activity has not previously been examined. It has been suggested that a dysfunction basic to schizophrenia spectrum traits would involve proprioceptive information processing and this has recently been supported by the finding of diminished latency of early proprioceptive evoked potentials in a sample of chronic schizophrenia patients. The proprioceptive stimulus used previously, and presently, consisted of an abrupt increase of weight on a hand-held load. Eighteen first-time admitted schizophrenia spectrum patients and 18 healthy matched comparison subjects were included. Proprioceptive evoked potentials were recorded as 64-channels EEG for 120 trials in two runs differing in sequence. Contra-lateral evoked beta (latency 90 ms, frequency 21 Hz) and gamma (latency 70 ms, frequency 32 Hz) oscillations were attenuated in the patient group. The healthy comparison subjects had increased gamma amplitude in the left hemisphere in the regular sequence, a phenomenon not seen in the patients. The deviant findings were unexpectedly more circumscribed in the schizophrenia than in the schizotypal personality disorder (SPD) patients. Future studies should include several concurrent psychophysiological measures.

Effect of mitochondrial toxins on evoked somatosensory activity in rats

AbstractMitochondrial toxins represent an interesting group of neurotoxicants related both to causation and modelling of central nervous damage. 3-nitropropionic acid (3NP), a neurotoxin of herbal and microfungal origin, inhibits succinate dehydrogenase leading thereby to various biochemical and morphological alterations in the brain. Experimental animals treated by 3NP are used to model Huntington’s disease. Manganese, often present in occupational settings and as environmental pollutant, inhibits complex II and III of the mitochondria and is known to cause Parkinson-like CNS damage. In this work, rats were administered a single acute dose of Mn (50 mg Mn2+/kg body weight) or 3-NP (20 mg/kg b.w.) and the alterations of the somatosensory cortical evoked potential elicited by stimulation of the whisker pad and the tail base were observed, together with the changes of the action potential in the tail nerve. Latency and amplitude of the two cortical responses changed in parallel, while those of the tail nerve response remained more or less unaltered. The two mitochondrial toxins studied seem to exert their action centrally, primarily on synaptic transmission, rather than peripherally. Recording of evoked activity could be used to follow-up the nervous system effects of mitochondrial toxins, but it requires further investigation.

Elevating intracranial pressure reverses the decrease in deoxygenated hemoglobin and abolishes the post-stimulus overshoot upon somatosensory activation in rats

BOLD fMRI localizes activated brain areas by measuring decreases of deoxygenated hemoglobin (deoxy-Hb) caused by neurovascular coupling. To date, it is unclear whether intracranial pressure (ICP) modifies deoxy-Hb signaling for brain mapping. In addition, ICP elevation can test whether the BOLD post-stimulus undershoot, a transient hypo-oxygenation following functional activation, is due to vascular compliance rather than elevated cerebral metabolic rate of oxygen (CMRO 2). We addressed these questions by studying the effect of ICP elevation on neurovascular coupling. In anesthetized rats, a cranial window was implanted over the somatosensory cortex. Using laser Doppler flowmetry and optical spectroscopy, changes in cerebral blood flow (CBF), cerebral blood volume (CBV) and deoxy-Hb were measured during electrical forepaw stimulation. Neuronal activity was monitored by somatosensory evoked potentials. ICP was elevated by subarachnoideal and intracisternal infusion of artificial cerebrospinal fluid. ICP elevation did not abrogate neurovascular coupling. However, the concomitant deoxy-Hb decrease was reduced (ICP = 14 mmHg) and reversed (ICP = 28 mmHg). Therefore, the validity of BOLD fMRI has to be questioned during increased ICP. Moreover, the amplitude of the deoxy-Hb post-stimulus overshoot was reduced with ICP elevation. CMRO 2 was not elevated during the post-stimulus response. Therefore, these data provide experimental evidence that the BOLD post-stimulus undershoot is a passive vascular phenomenon.

Dynamical activities of primary somatosensory cortices studied by magnetoencephalography

A blind identification method of transfer functions in feedback systems is introduced for examination of dynamical activities of cortices by magnetoencephalography study. Somatosensory activities are examined in 5 Hz periodical median nerve stimulus. In the present paper, we will try two careful preprocessing procedures for the identification method to obtain impulse responses between primary somatosensory cortices. Time series data of the somatosensory evoked field are obtained by using a blind source separation of the T/k type (fractional) decorrelation method. Time series data of current dipoles of primary somatosensory cortices are transformed from the time series data of the somatosensory evoked field by the inverse problem. Fluctuations of current dipoles of them are obtained after elimination of deterministic periodical evoked waveforms. An identification method based on feedback system theory is used for estimation of transfer functions in a feedback model from obtained fluctuations of currents dipoles of primary somatosensory cortices. Dynamical activities between them are presented by Bode diagrams of transfer functions and their impulse responses: the time delay of about 30 ms via corpus callosum is found in the impulse response of identified transfer function.

When seeing outweighs feeling: a role for prefrontal cortex in passive control of negative affect in blindsight

Affective neuroscience has been strongly influenced by the view that a ‘feeling’ is the perception of somatic changes and has consequently often neglected the neural mechanisms that underlie the integration of somatic and other information in affective experience. Here, we investigate affective processing by means of functional magnetic resonance imaging in nine cortically blind patients. In these patients, unilateral postgeniculate lesions prevent primary cortical visual processing in part of the visual field which, as a result, becomes subjectively blind. Residual subcortical processing of visual information, however, is assumed to occur in the entire visual field. As we have reported earlier, these patients show significant startle reflex potentiation when a threat-related visual stimulus is shown in their blind visual field. Critically, this was associated with an increase of brain activity in somatosensory-related areas, and an increase in experienced negative affect. Here, we investigated the patients’ response when the visual stimulus was shown in the sighted visual field, that is, when it was visible and cortically processed. Despite the fact that startle reflex potentiation was similar in the blind and sighted visual field, patients reported significantly less negative affect during stimulation of the sighted visual field. In other words, when the visual stimulus was visible and received full cortical processing, the patients’ phenomenal experience of affect did not closely reflect somatic changes. This decoupling of phenomenal affective experience and somatic changes was associated with an increase of activity in the left ventrolateral prefrontal cortex and a decrease of affect-related somatosensory activity. Moreover, patients who showed stronger left ventrolateral prefrontal cortex activity tended to show a stronger decrease of affect-related somatosensory activity. Our findings show that similar affective somatic changes can be associated with different phenomenal experiences of affect, depending on the depth of cortical processing. They are in line with a model in which the left ventrolateral prefrontal cortex is a relay station that integrates information about subcortically triggered somatic responses and information resulting from in-depth cortical stimulus processing. Tentatively, we suggest that the observed decoupling of somatic responses and experienced affect, and the reduction of negative phenomenal experience, can be explained by a left ventrolateral prefrontal cortex-mediated inhibition of affect-related somatosensory activity.

Influence of Dopaminergically Mediated Reward on Somatosensory Decision-Making

Author SummaryThe rewards one receives during decision-making has a profound impact on learning. Much recent interest has focused on the role of the neurotransmitter dopamine in the basal ganglia for influencing learning and behaviour. Here, we ask whether reward can influence low-level sensory processing, for instance in primary sensory cortex, and how dopamine mediates this process. We show in humans that dopamine level, as manipulated with a dopamine agonist and antagonist in a double-blind placebo-controlled design, is involved in reward modulation of primary somatosensory cortex. Higher anticipated reward improved tactile decisions, and receipt of visual reward signals reactivated primary somatosensory cortex for the judged hand as measured using functional neuroimaging. After receiving a higher reward on one trial, somatosensory activations and decisions were enhanced on the next trial, suggesting that reward outcome provides a form of teaching signal that may be fed back to task-relevant sensory cortex. All these behavioural and neural effects of reward on somatosensory decision-making were strongly modulated by the availability of dopamine as the mediating neurotransmitter. These findings raise the tantalising new possibility that reward manipulations in conjunction with dopaminergic drugs might be used to enhance pathologically deficient or lapsed sensory processes, analogous to how rewards can be used to shape or correct behaviour.

Design, construction, and validation of an MRI-compatible vibrotactile stimulator intended for clinical use

Vibrotactile stimulation has been used successfully to activate the human somatosensory pathway in functional magnetic resonance imaging (fMRI) experiments. The design and characterization of these devices are of particular interest in frequency discrimination tasks and investigations of the somatopic organization of sensory areas. However, few have investigated the utility of vibrotactile stimulation in a clinical context. We have previously demonstrated that vibrotactile stimulation can provide robust activations in areas targeted in stereotactic functional neurosurgical procedures used for tumour resection (i.e.: primary and secondary somatosensory areas) and subcortical targets for thalamic pain and movement disorders (i.e.: sensory thalamus). The main contribution of this manuscript is the presentation of the design, materials, construction, and validation of a novel vibrotactile stimulator intended for clinical use. The thalamic activations are also compared to a digital atlas in order to evaluate anatomical localization. The proposed stimulator was constructed entirely from non-ferromagnetic parts, uses compressed air to deliver stimulation using computer control, and stimulates the entirety of the hand and fingers to ensure robust somatosensory activations. In addition, this stimulator is constructed entirely from “off-the-shelf” parts and would be easily replicated due to the simplicity of design and the relatively small expense of the parts required. The device was tested by stimulating the right hand of 10 normal controls (5 females, 5 males, all right handed; age range: 25–42 years, mean: 30.9 years, standard deviation: 5.2 years) during an fMRI experiment. The results demonstrate significant single subject activations of primary and secondary somatosensory cortices and of the sensory thalamus.

Somatosensory Cortex Activation by a Visual Stimulus that Signals Shock

Somatosensory Cortex Activation by a Visual Stimulus that Signals Shock

Effect of cyclooxygenase-2 on the regulation of cerebral blood flow during neuronal activation in the rat

The present study was designed to clarify the precision of the main approach for investigating the regulation of local cerebral blood flow (CBF) response to neuronal activation in the brain (neurovascular coupling). In this study, we examined the effects of NS-398, a highly selective cyclooxygenase-2 inhibitor, on the physiological variables, baseline CBF, and local CBF response during rat somatosensory neuronal activation by laser-Doppler flowmetry. Blood pressure and heart rate were significantly decreased 3 h after i.v. infusion of NS-398. Baseline CBF and local CBF during somatosensory activation gradually decreased with an increase in time of NS-398 infusion up to 3 h, although neuronal activity in the somatosensory area was almost constant during the infusion. The results suggest that cyclooxygenase-2 participates in the regulation of local CBF during neuronal activation in rats. The present study also revealed the potential side-effects of dimethylsulfoxide, a solvent of NS-398, on neurovascular coupling.

Abnormal cerebral metabolism during menstrual pain in primary dysmenorrhea

Primary dysmenorrhea (PDM, menstrual pain without pelvic abnormality) is the most common gynecological disorder for women in the reproductive age. It is characterized by cramping pain and enhanced pain sensitivity during the menstruation period. PDM has been associated with peripheral and central sensitization. Abnormal brain mechanisms may further contribute to development and maintenance of the state. Using fluoro-deoxyglucose positron emission tomography, increased activity was observed in prefrontal/orbitofrontal regions and left ventral posterior thalamus while decreased activity mainly was observed in sensorimotor regions of the left hemisphere at onset compared to offset of PDM. These results were specific to menstrual pain and were not found in menstrual matched controls. Orbitofrontal activities were positively related to while somatosensory activities where negatively related to subjective pain ratings. These results show that ongoing menstrual pain in PDM is accompanied by abnormal brain metabolism. Disinhibition of thalamo-orbitofrontal-prefrontal networks may contribute to the generation of pain and hyperalgesia in PDM possibly by maintaining spinal and thalamic sensitization while increasing negative affect. Excessive excitatory input during menstrual pain may induce compensatory inhibitory mechanism in several somatic sensorimotor regions.

Empathic neural responses to others' pain are modulated by emotional contexts

Recent brain imaging studies indicate that empathy for pain relies upon both the affective and/or the sensorimotor nodes of the pain matrix, and empathic neural responses are modulated by stimulus reality, personal experience, and affective link with others. The current work investigated whether and how empathic neural responses are modulated by emotional contexts in which painful stimulations are perceived. Using functional magnetic resonance imaging (fMRI), we first showed that perceiving a painful stimulation (needle penetration) applied to a face with neutral expression induced activation in the anterior cingulate cortex (ACC) relative to nonpainful stimulation (Q-tip touch). However, when observation of the painful stimuli delivered to a neutral face was intermixed with observation of painful or happy faces, the ACC activity decreased while the activity in the face area of the secondary somatosensory cortex increased to the painful stimulation. Moreover, the secondary somatosensory activity associated with the painful stimulation decreased when the painful stimulation was applied to faces with happy and painful expressions. The findings suggest that observing painful stimuli in an emotional context weakens affective responses but increases sensory responses to perceived pain and implies possible interactions between the affective and sensory components of the pain matrix during empathy for pain.

Effects of different viewing perspectives on somatosensory activations during observation of touch

Previous studies showed that neurons in the monkey premotor cortex became active when performing a particular action and also when observing the same action performed by others. These findings suggest a mirror system for action observation. Recently, bimodal neurons, sensitive both to visual and tactile stimulation, were reported in the parietal cortex, suggesting a potential mirror neuron system for observing and experiencing tactile stimulation. Subsequently, a mirror neuron system for observed touch has been suggested. The current study was designed to determine whether the activation of a sensory mirror system during touch observation is affected by possible attributions of the observed touch to oneself (subjective view) or to somebody else (objective view). In the study, healthy volunteers observed video clips of a touched or nontouched hand either in an egocentric or in an allocentric perspective during functional magnetic resonance imaging. Results showed activation of somatosensory cortices when observing the hand being touched in egocentric as well as in the allocentric perspectives. Moreover, somatosensory responses differed depending on the perspective of the observed touch. We discuss the results in terms of a possible mirror neuron system for observed and experienced touch.

Effects of COX-2 inhibitor on CBF regulation during somatosensory activation in rats

Effects of COX-2 inhibitor on CBF regulation during somatosensory activation in rats

Expansion of somatosensory activity onto visual structures in the congenital anophthalmic mouse

Expansion of somatosensory activity onto visual structures in the congenital anophthalmic mouse

Progressive changes in sleep electroencephalogram dynamics in the rat barrel cortex associated with long-term alternation of sensory input activities

Sleep is suggested to be involved in the development and maintenance of neural networks. We investigated how long-term alternation of somatosensory input activities affects electroencephalogram (EEG) dynamics of adult rats during non-REM sleep (NREM). Power spectral densities of NREM EEG activity were analyzed for 10 days under the alternation of sensory input activities caused by unilateral whisker clipping. The progressive reduction of the delta power of the inactivated side of the barrel cortex relative to the activated side was found in terms of the daily mean. This extends our previous study in which only the initial 4-h data in every light period was analyzed. In addition, the circadian variation in power spectral densities of NREM EEG activities in the barrel and visual cortices was found to consist of a common background component and fractional regional difference. Averaging out the background circadian variations and canceling the day-to-day variations and inter-individual differences revealed the progressive monotonic increase and decrease in the delta-band spectral powers in the activated side and inactivated side of barrel cortex, respectively. This concurrent and mutually opposite progressive change in the delta power in NREM might reflect the reorganization process of the cortical circuit, especially inhibitory synaptic transmission, rather than the short-term usage-dependent regional regulation of sleep.

Functional topography in the human cerebellum: A meta-analysis of neuroimaging studies

Clinical, experimental and neuroimaging studies indicate that the cerebellum is involved in neural processes beyond the motor domain. Cerebellar somatotopy has been shown for motor control, but topographic organization of higher-order functions has not yet been established. To determine whether existing literature supports the hypothesis of functional topography in the human cerebellum, we conducted an activation likelihood estimate (ALE) meta-analysis of neuroimaging studies reporting cerebellar activation in selected task categories: motor ( n = 7 studies), somatosensory ( n = 2), language ( n = 11), verbal working memory ( n = 8), spatial ( n = 8), executive function ( n = 8) and emotional processing ( n = 9). In agreement with previous investigations, sensorimotor tasks activated anterior lobe (lobule V) and adjacent lobule VI, with additional foci in lobule VIII. Motor activation was in VIIIA/B; somatosensory activation was confined to VIIIB. The posterior lobe was involved in higher-level tasks. ALE peaks were identified in lobule VI and Crus I for language and verbal working memory; lobule VI for spatial tasks; lobules VI, Crus I and VIIB for executive functions; and lobules VI, Crus I and medial VII for emotional processing. Language was heavily right-lateralized and spatial peaks left-lateralized, reflecting crossed cerebro-cerebellar projections. Language and executive tasks activated regions of Crus I and lobule VII proposed to be involved in prefrontal-cerebellar loops. Emotional processing involved vermal lobule VII, implicated in cerebellar-limbic circuitry. These data provide support for an anterior sensorimotor vs. posterior cognitive/emotional dichotomy in the human cerebellum. Prospective studies of multiple domains within single individuals are necessary to better elucidate neurobehavioral structure–function correlations in the cerebellar posterior lobe.