Prominent activation of the intraparietal and somatosensory areas during angle discrimination by intra-active touch

Intra‐active touch (IAT) is a process that involves a body part doing the touching (active touch [AT]) and another body part being touched (passive touch [PT]) simultaneously. The brain representation related to IAT is still unclear. A total of 23 subjects carried out angle discrimination under PT, AT and IAT conditions with functional magnetic resonance imaging. All of the tasks were strictly dependent on cutaneous feedback from the finger(s). As the subjects were able to perceive the angle stimuli from the right (touching) and left (touched) sides during the IAT condition, we expected there would be greater brain activation with the IAT condition than for the AT or PT condition. Therefore, we hypothesized that the region within and/or around the intraparietal sulcus (IPS) and the part of the primary somatosensory cortex (SI) that is associated with high‐level tactile spatial processing would be more active during the IAT task than during the AT and PT tasks. Compared with the areas activated by the motor somatosensory control task, the most prominent activation areas evoked by the three‐angle discrimination tasks were in the SI and secondary somatosensory cortex areas in the bilateral parietal operculum, IPS, lateral occipital complex, insula and cerebellum. Finally, we directly compared IAT with AT and PT, and the results suggest that the contralateral part of IPS and part of the SI are more active under IAT conditions than under either AT or PT conditions. These results suggest that both hemispheres contribute to angle discrimination during IAT. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.     

Neural correlates of top‐down modulation of haptic shape versus roughness perception

Exploring an object's shape by touch also renders information about its surface roughness. It has been suggested that shape and roughness are processed distinctly in the brain, a result based on comparing brain activation when exploring objects that differed in one of these features. To investigate the neural mechanisms of top‐down control on haptic perception of shape and roughness, we presented the same multidimensional objects but varied the relevance of each feature. Specifically, participants explored two objects that varied in shape (oblongness of cuboids) and surface roughness. They either had to compare the shape or the roughness in an alternative‐forced‐choice‐task. Moreover, we examined whether the activation strength of the identified brain regions as measured by functional magnetic resonance imaging (fMRI) can predict the behavioral performance in the haptic discrimination task. We observed a widespread network of activation for shape and roughness perception comprising bilateral precentral and postcentral gyrus, cerebellum, and insula. Task‐relevance of the object's shape increased activation in the right supramarginal gyrus (SMG/BA 40) and the right precentral gyrus (PreCG/BA 44) suggesting that activation in these areas does not merely reflect stimulus‐driven processes, such as exploring shape, but also entails top‐down controlled processes driven by task‐relevance. Moreover, the strength of the SMG/PreCG activation predicted individual performance in the shape but not in the roughness discrimination task. No activation was found for the reversed contrast (roughness > shape). We conclude that macrogeometric properties, such as shape, can be modulated by top‐down mechanisms whereas roughness, a microgeometric feature, seems to be processed automatically.     

ALE meta‐analysis reveals dissociable networks for affective and discriminative aspects of touch

Emotionally‐laden tactile stimulation—such as a caress on the skin or the feel of velvet—may represent a functionally distinct domain of touch, underpinned by specific cortical pathways. In order to determine whether, and to what extent, cortical functional neuroanatomy supports a distinction between affective and discriminative touch, an activation likelihood estimate (ALE) meta‐analysis was performed. This meta‐analysis statistically mapped reported functional magnetic resonance imaging (fMRI) activations from 17 published affective touch studies in which tactile stimulation was associated with positive subjective evaluation (n = 291, 34 experimental contrasts). A separate ALE meta‐analysis mapped regions most likely to be activated by tactile stimulation during detection and discrimination tasks (n = 1,075, 91 experimental contrasts). These meta‐analyses revealed dissociable regions for affective and discriminative touch, with posterior insula (PI) more likely to be activated for affective touch, and primary somatosensory cortices (SI) more likely to be activated for discriminative touch. Secondary somatosensory cortex had a high likelihood of engagement by both affective and discriminative touch. Further, meta‐analytic connectivity (MCAM) analyses investigated network‐level co‐activation likelihoods independent of task or stimulus, across a range of domains and paradigms. Affective‐related PI and discriminative‐related SI regions co‐activated with different networks, implicated in dissociable functions, but sharing somatosensory co‐activations. Taken together, these meta‐analytic findings suggest that affective and discriminative touch are dissociable both on the regional and network levels. However, their degree of shared activation likelihood in somatosensory cortices indicates that this dissociation reflects functional biases within tactile processing networks, rather than functionally and anatomically distinct pathways. Hum Brain Mapp 37:1308‐1320, 2016. © 2016 Wiley Periodicals, Inc.     

Transfer of the curvature aftereffect in dynamic touch

A haptic curvature aftereffect is a phenomenon in which the perception of a curved shape is systematically altered by previous contact to curvature. In the present study, the existence and intermanual transfer of curvature aftereffects for dynamic touch were investigated. Dynamic touch is characterized by motion contact between a finger and a stimulus. A distinction was made between active and passive contact of the finger on the stimulus surface. We demonstrated the occurrence of a dynamic curvature aftereffect and found a complete intermanual transfer of this aftereffect, which suggests that dynamically obtained curvature information is represented at a high level. In contrast, statically perceived curvature information is mainly processed at a level that is connected to a single hand, as previous studies indicated. Similar transfer effects were found for active and passive dynamic touch, but a stronger aftereffect was obtained when the test surface was actively touched. We conclude that the representation of object information depends on the exploration mode that is used to acquire information.     

Attention to touch modulates activity in both primary and secondary somatosensory areas

We used fMRI to establish whether attention to touch enhances somatosensory cortical activity. Subjects received somatosensory and visual stimulation and were instructed to attend selectively to one modality during alternating stimulus detection periods interspersed with rest periods during which no stimulus was delivered. The maximum signal change for each task versus rest was measured in anatomically defined regions of interest for each subject. Attended touch produced greater signal change than unattended touch in primary (S1) and secondary (S2) somatosensory cortex. In contrast to the conclusions of some previous studies, we found that the enhancement of activation with attention was at least as great in S1 as in S2. The attentional effect was unilateral in S1 and bilateral in S2 and the somatosensory insula.     

Rough primes and rough conversations: evidence for a modality-specific basis to mental metaphors

How does our brain organize knowledge? Traditional theories assume that our knowledge is represented abstractly in an amodal conceptual network of formal logic symbols. The theory of embodied cognition challenges this view and argues that conceptual representations that constitute our knowledge are grounded in sensory and motor experiences. We tested this hypothesis by examining how the concept of social coordination is grounded metaphorically in the tactile sensation of roughness. Participants experienced rough or smooth touch before being asked to judge an ambiguous social interaction. Results revealed that rough touch made social interactions appear more difficult and adversarial, consistent with the rough metaphor. This impact of tactile cues on social impressions was accompanied by a network including primary and secondary somatosensory cortices, amygdala, hippocampus and inferior prefrontal cortex. Thus, the roughness of tactile stimulation affected metaphor-relevant (but not metaphor-irrelevant) behavioral and neural responses. Receiving touch from a rough object seems to trigger the application of associated ontological concepts (or scaffolds) even for unrelated people and situations (but not to unrelated or more general feelings). Since this priming was based on somatosensory brain areas, our results provide support for the theory that sensorimotor grounding is intrinsic to cognitive processes.     

A PET Study of Somatosensory Discrimination in Man. Microgeometry Versus Macrogeometry

The regional cerebral blood flow (rCBF) was measured with ¹⁵O-butanol and positron emission tomography (PET) in 10 healthy subjects in order to compare cerebral activation involved in the somatosensory discrimination of microgeometric features with cerebral activation associated with the discrimination of macrogeometric features. Subjects performed two-alternative forced choice (2-AFC) discriminations of pairs of stimuli from a series of quantified standardized stimuli that differed in roughness (microgeometry), and a separate 2-AFC task of smooth tactile stimuli that differed in length (macrogeometry). Results are presented from three conditions: (1) a roughness discrimination task; (2) a length discrimination task; and (3) a control trial in which subjects were required to reproduce similar exploratory finger movements only, but without a specific stimulus to feel. Mean subtraction images were computed using the computerized adjustable brain atlas of Greitz et al. (1991, J. Comput. Assisted Tomogr., 15, 26–38) and areas of significant blood flow change were identified. Both the roughness and the length discrimination tasks activated overlapping cortical fields contralaterally in the anterior and posterior lip of the postcentral sulcus. However, in the length discrimination, activation of the posterior lip of the postcentral sulcus extended deeper into the sulcus and there was also a separate additional area of activation in the anterior part of the precentral gyrus. Furthermore, the length discrimination task activated fields in the overt part of the supramarginal gyrus bilaterally as well as fields in the angular gyrus bilaterally. Thus roughness discrimination uses only a subset of the cortical regions that are needed for the recovery of length information, which requires more extensive somatosensory processing. This finding may be partly explained in that length perception needs both edge detection of the stimuli used, as well as integrated information of surface length and velocity, which is not necessary for roughness perception. Specific differences in the acquisition of necessary tactile information between the two discrimination tasks was reflected in different sampling strategies.     

Changes in cortical negative DC shifts due to different motor task conditions.

The experiments were performed to study the relationship between motor performance and DC potential curves recorded by scalp electrodes. Accordingly, we studied the influence of different movements (e.g., unilateral versus bilateral, simple versus complex, active versus passive, phasic versus tonic muscle activity) on negative DC potentials. Our results confirm that spatial distributions of DC potential maxima can be used as an indicator of the activation of distinct cortical areas. Furthermore, evidence is presented that some motor tasks have a greater influence on the magnitude of surface electronegativity than others. (1) Phasic muscle activity revealed a significantly larger potential size than tonic. (2) Performance of a complex finger movement task elicited an increased surface electronegativity compared with performance of a simple task. (3) No significant differences in potential size were found between left (untrained) and right (skilled) hand use during the performance of the same complex motor task. (4) This was also true for the performance of an active and a passive finger movement task, indicating that, at least in simple motor tasks, somatosensory afferents significantly contribute to the recorded potential curve.     

Maternal sensitivity and infant neural response to touch: an fNIRS study

The mother’s attunement to her infant’s emotional needs influences her use of touching behaviors during mother–infant interactions. Moreover, maternal touch appears to modulate infants’ physiological responses to affective touch. However, little is known about the impact of maternal sensitivity on infants’ touch processing at a brain level. This study explored the association between maternal sensitivity when infants (N = 24) were 7 months old and their patterns of cortical activation to touch at 12 months. Brain activation was measured using functional near-infrared spectroscopy. Changes in oxy-hemoglobin (HbO₂) and deoxy-hemoglobin (HHb) concentrations were measured in the left somatosensory cortex and right temporal cortex while infants received two types of tactile stimulation—affective and discriminative touch. Results showed that a lower maternal sensitivity was associated with a higher HbO₂ response for discriminative touch over the temporal region. Additionally, infants of less sensitive mothers tended to present a higher response in HbO₂ for affective touch over the somatosensory region. These findings suggest that less sensitive interactions might result in a lower exposure to maternal touch, which can be further related to infants’ neural processing of touch.     

Neural correlates of gentle skin stroking in early infancy

Physical expressions of affection play a foundational role in early brain development, but the neural correlates of affective touch processing in infancy remain unclear. We examined brain responses to gentle skin stroking, a type of tactile stimulus associated with affectionate touch, in young infants. Thirteen term-born infants aged 11–36 days, recruited through the FinnBrain Birth Cohort Study, were included in the study. Soft brush strokes, which activate brain regions linked to somatosensory as well as socio-affective processing in children and adults, were applied to the skin of the right leg during functional magnetic resonance imaging. We examined infant brain responses in two regions-of-interest (ROIs) known to process gentle skin stroking – the postcentral gyrus and posterior insular cortex – and found significant responses in both ROIs. These results suggest that the neonate brain is responsive to gentle skin stroking within the first weeks of age, and that regions linked to primary somatosensory as well as socio-affective processing are activated. Our findings support the notion that social touch may play an important role in early life sensory processing. Future research will elucidate the significance of these findings for human brain development.     

Hand or spoon? Exploring the neural basis of affective touch in 5-month-old infants

In adults, affective touch leads to widespread activation of cortical areas including posterior Superior Temporal Sulcus (pSTS) and Inferior Frontal Gyrus (IFG). Using functional Near Infrared Spectroscopy (fNIRS), we asked whether similar areas are activated in 5-month-old infants, by comparing affective to non-affective touch. We contrasted a human touch stroke to strokes performed with a cold metallic spoon. The hypothesis that adult-like activation of cortical areas would be seen only in response to the human touch stroke was not confirmed. Similar patterns of activation were seen in both conditions. We conclude that either the posterior STS and IFG have not yet developed selective responses to affective touch, or that additional social cues are needed to be able to identify this type of touch.     

Judging roughness by sight—A 7‐tesla fMRI study on responsivity of the primary somatosensory cortex during observed touch of self and others

Observing another person being touched activates our own somatosensory system. Whether the primary somatosensory cortex (S1) is also activated during the observation of passive touch, and which subregions of S1 are responsible for self‐ and other‐related observed touch is currently unclear. In our study, we first aimed to clarify whether observing passive touch without any action component can robustly increase activity in S1. Secondly, we investigated whether S1 activity only increases when touch of others is observed, or also when touch of one's own body is observed. We were particularly interested in which subregions of S1 are responsible for either process. We used functional magnetic resonance imaging at 7 Tesla to measure S1 activity changes when participants observed videos of their own or another's hand in either egocentric or allocentric perspective being touched by different pieces of sandpaper. Participants were required to judge the roughness of the different sandpaper surfaces. Our results clearly show that S1 activity does increase in response to observing passive touch, and that activity changes are localized in posterior but not in anterior parts of S1. Importantly, activity increases in S1 were particularly related to observing another person being touched. Self‐related observed touch, in contrast, caused no significant activity changes within S1. We therefore assume that posterior but not anterior S1 is part of a system for sharing tactile experiences with others. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.     

功能MRI和弥散张量纤维束示踪成像联合应用是评估脑出血患者躯体感觉功能恢复的有用工具？1例报告

研究背景：目前对中风之后的身体感觉机能障碍了解很少。 研究目的：我们试图证明应用功能性磁共振成像(fMRI)和扩散张量纤维束示踪(DTT)能使颅内出血(ICH)患者的身体感觉机能障碍康复。 研究设计,时间和地点：从2008年6月到11月在理疗与康复教研室进行病例研究。 参与人员：55岁的女患者,她起先右侧皮质和辐射冠自发性的颅内出血,造成左身严重的身体感觉机能障碍。 研究方法：应用PHILIPS公司Gyroscan Intera 1 .5 T扩散张量纤维束示踪系统和磁共振成像系统从开始之后的3-7周进行两个纵向评估。扩散张量纤维束示踪以分次的各向异性<0.2作为最终标准,磁共振成像通过手的触摸和被动运动来完成. 主要成果: 我们发现扩散张量纤维束示踪过程和磁共振成像上的皮质激活是伴随着身体感觉功能的恢复一起的. 研究结果: 受作用的一边在开始之后的第7周身体感觉功能会恢复到接近于正常的状态.从第3到7周的功能性磁共振成像上我们发现, 位于另一侧初级感觉皮质中心的皮质被活化.然而,在第3周的磁共振成像上却没有发生皮质激活功能而被动运动的激活功能在第7周比第3周显示的有所增强.在第3周对受创一侧(右侧)扩散张量纤维束示踪中我们没能发现内侧丘系.第7周的内侧丘系示踪, 一个内侧丘系沿着丘系内侧从辐射冠上升到初级感觉皮质. 结论: 我们证明了在这位患者的身体感觉机能恢复中应用到了功能性磁共振成像(fMRI)和扩散张量纤维束示踪(DTT). 我们推断在研究中风病人的身体感觉机能障碍的康复中功能性磁共振成像(fMRI)和扩散张量纤维束示踪(DTT)是有效的方法.     

Cortical brain responses during passive nonpainful median nerve stimulation at low frequencies (0.5-4 Hz): an fMRI study

Previous findings have shown that the human somatosensory cortical systems that are activated by passive nonpainful electrical stimulation include the contralateral primary somatosensory area (SI), bilateral secondary somatosensory area (SII), and bilateral insula. The present study tested the hypothesis that these areas have different sensitivities to stimulation frequency in the condition of passive stimulation. Functional MRI (fMRI) was recorded in 24 normal volunteers during nonpainful electrical median nerve stimulations at 0.5, 1, 2, and 4 Hz repetition rates in separate recording blocks in pseudorandom order. Results of the blood oxygen level-dependent (BOLD) effect showed that the contralateral SI, the bilateral SII, and the bilateral insula were active during these stimulations. As a major finding, only the contralateral SI increased its activation with the increase of the stimulus frequency at the mentioned range. The fact that nonpainful median-nerve electrical stimuli at 4 Hz induces a larger BOLD response is of interest both for basic research and clinical applications in subjects unable to perform cognitive tasks in the fMRI scanner.     

Spatiotemporal dynamics of bimanual integration in human somatosensory cortex and their relevance to bimanual object manipulation

Little is known about the spatiotemporal dynamics of cortical responses that integrate slightly asynchronous somatosensory inputs from both hands. This study aimed to clarify the timing and magnitude of interhemispheric interactions during early integration of bimanual somatosensory information in different somatosensory regions and their relevance for bimanual object manipulation and exploration. Using multi-fiber probabilistic diffusion tractography and MEG source analysis of conditioning-test (C-T) median nerve somatosensory evoked fields in healthy human subjects, we sought to extract measures of structural and effective callosal connectivity between different somatosensory cortical regions and correlated them with bimanual tactile task performance. Neuromagnetic responses were found in major somatosensory regions, i.e., primary somatosensory cortex SI, secondary somatosensory cortex SII, posterior parietal cortex, and premotor cortex. Contralateral to the test stimulus, SII activity was maximally suppressed by 51% at C-T intervals of 40 and 60 ms. This interhemispheric inhibition of the contralateral SII source activity correlated directly and topographically specifically with the fractional anisotropy of callosal fibers interconnecting SII. Thus, the putative pathway that mediated inhibitory interhemispheric interactions in SII was a transcallosal route from ipsilateral to contralateral SII. Moreover, interhemispheric inhibition of SII source activity correlated directly with bimanual tactile task performance. These findings were exclusive to SII. Our data suggest that early interhemispheric somatosensory integration primarily occurs in SII, is mediated by callosal fibers that interconnect homologous SII areas, and has behavioral importance for bimanual object manipulation and exploration.     

Eye muscle proprioception is represented bilaterally in the sensorimotor cortex

The cortical representation of eye position is still uncertain. In the monkey a proprioceptive representation of the extraocular muscles (EOM) of an eye were recently found within the contralateral central sulcus. In humans, we have previously shown a change in the perceived position of the right eye after a virtual lesion with rTMS over the left somatosensory area. However, it is possible that the proprioceptive representation of the EOM extends to other brain sites, which were not examined in these previous studies. The aim of this fMRI study was to sample the whole brain to identify the proprioceptive representation for the left and the right eye separately. Data were acquired while passive eye movement was used to stimulate EOM proprioceptors in the absence of a motor command. We also controlled for the tactile stimulation of the eyelid by removing from the analysis voxels activated by eyelid touch alone. For either eye, the brain area commonly activated by passive and active eye movement was located bilaterally in the somatosensory area extending into the motor and premotor cytoarchitectonic areas. We suggest this is where EOM proprioception is processed. The bilateral representation for either eye contrasts with the contralateral representation of hand proprioception. We suggest that the proprioceptive representation of the two eyes next to each other in either somatosensory cortex and extending into the premotor cortex reflects the integrative nature of the eye position sense, which combines proprioceptive information across the two eyes with the efference copy of the oculomotor command.     

Neural time-course of the observation of human and non-human object touch

Recent functional magnetic resonance imaging studies have reported activation of primary and secondary somatosensory cortices when participants observe another person or object being touched. In this study, we used event-related potentials to examine the nature and time-course of the neural mechanisms associated with the observation of humans and non-human objects being touched. Participants were presented with short video clips of a human arm or a non-human cylindrical object being touched by an object, compared with an object moving in front of the arms or cylinders without touching them. Touch vs non-touch effects were observed in the amplitudes of the N100 and N250 components, as well as a late slow wave component (500–600 ms), measured from electrodes over primary somatosensory cortex. Human vs non-human stimulus effects were reflected in the latencies of the N100, P170 and N250 components recorded over somatosensory cortex, as well as the temporal–parietal visual-perceptual N170 and N250 components. These findings suggest that human and non-human touch observation are associated with somatosensory processing at both an early sensory-perceptual stage and a relatively late cognitive stage, both preceding and following the perceptual encoding of the humanness of stimuli that typically occurs in extrastriate visual areas.     

The neural substrate for working memory of tactile surface texture

Fine surface texture is best discriminated by touch, in contrast to macro geometric features like shape. We used functional magnetic resonance imaging and a delayed match‐to‐sample task to investigate the neural substrate for working memory of tactile surface texture. Blindfolded right‐handed males encoded the texture or location of up to four sandpaper stimuli using the dominant or non‐dominant hand. They maintained the information for 10–12 s and then answered whether a probe stimulus matched the memory array. Analyses of variance with the factors Hand, Task, and Load were performed on the estimated percent signal change for the encoding and delay phase. During encoding, contralateral effects of Hand were found in sensorimotor regions, whereas Load effects were observed in bilateral postcentral sulcus (BA2), secondary somatosensory cortex (S2), pre‐SMA, dorsolateral prefrontal cortex (dlPFC), and superior parietal lobule (SPL). During encoding and delay, Task effects (texture > location) were found in central sulcus, S2, pre‐SMA, dlPFC, and SPL. The Task and Load effects found in hand‐ and modality‐specific regions BA2 and S2 indicate involvement of these regions in the tactile encoding and maintenance of fine surface textures. Similar effects in hand‐ and modality‐unspecific areas dlPFC, pre‐SMA and SPL suggest that these regions contribute to the cognitive monitoring required to encode and maintain multiple items. Our findings stress both the particular importance of S2 for the encoding and maintenance of tactile surface texture, as well as the supramodal nature of parieto‐frontal networks involved in cognitive control. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.     

The Right Hemisphere’s Role in Action Word Processing: a Double Case Study.

Word category-specific deficits were investigated in two patients with right hemispheric lesions and hemiparesis affecting the left extremities. Words from three categories, action verbs, nouns with strong visual associations and nouns with both strong action and visual associations, were presented in a lexical decision task. The stimulus categories were matched for word length and frequency. In both patients, responses to action verbs were slowed and/or less accurate compared with the other word categories. This was so even in the patient with a minor lesion in the motor, pre-motor and somatosensory areas of the hand representation. Control subjects did not show category differences when tested with the same stimulus materials. These results are consistent with the view that the cortical areas involved in the programming of body movements, even those in the hemisphere not dominant for language, specifically contribute to and are necessary for the processing of words referring to such movements. As an alternative, the affected brain areas may be of particular relevance for the processing of words from the lexical category of verbs. The results are consistent with a brain model of language based on Hebb’s cell assembly concept.     

The right hemisphere's role in action word processing: a double case study

Word category-specific deficits were investigated in two patients with right hemispheric lesions and hemiparesis affecting the left extremities. Words from three categories, action verbs, nouns with strong visual associations and nouns with both strong action and visual associations, were presented in a lexical decision task. The stimulus categories were matched for word length and frequency. In both patients, responses to action verbs were slowed and/or less accurate compared with the other word categories. This was so even in the patient with a minor lesion in the motor, pre-motor and somatosensory areas of the hand representation. Control subjects did not show category differences when tested with the same stimulus materials. These results are consistent with the view that the cortical areas involved in the programming of body movements, even those in the hemisphere not dominant for language, specifically contribute to and are necessary for the processing of words referring to such movements. As an alternative, the affected brain areas may be of particular relevance for the processing of words from the lexical category of verbs. The results are consistent with a brain model of language based on Hebb's cell assembly concept.