Esther Kuehn

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 ones 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 anothers 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.

Body Topography Parcellates Human Sensory and Motor Cortex

Abstract The cytoarchitectonic map as proposed by Brodmann currently dominates models of human sensorimotor cortical structure, function, and plasticity. According to this model, primary motor cortex, area 4, and primary somatosensory cortex, area 3b, are homogenous areas, with the major division lying between the two. Accumulating empirical and theoretical evidence, however, has begun to question the validity of the Brodmann map for various cortical areas. Here, we combined in vivo cortical myelin mapping with functional connectivity analyses and topographic mapping techniques to reassess the validity of the Brodmann map in human primary sensorimotor cortex. We provide empirical evidence that area 4 and area 3b are not homogenous, but are subdivided into distinct cortical fields, each representing a major body part (the hand and the face). Myelin reductions at the hand–face borders are cortical layer-specific, and coincide with intrinsic functional connectivity borders as defined using large-scale resting state analyses. Our data extend the Brodmann model in human sensorimotor cortex and suggest that body parts are an important organizing principle, similar to the distinction between sensory and motor processing.

On the bimanual integration of proprioceptive information.

Proprioception can be defined as the sense for body movement and position. While most sensory information can be successfully integrated across hemispheres, little is known about the bilateral integration of proprioceptive information. In two behavioural experiments, we investigated whether estimates of the position of one hand are influenced by simultaneous proprioceptive information from the other hand. We further investigated whether such putative bimanual proprioceptive integration would differ between expert dancers and non-dancer controls. Either one hand or both hands were passively moved to novel positions, and participants indicated the perceived location of the index finger tip of the designated target hand, by orienting a visible laser beam mounted on a cap. Synchronized bimanual movements compared to unimanual movements significantly improved proprioceptive position sense. In particular, we found a bias reduction to perceive the target hand’s index finger tip as shifted away from the midline in the bimanual condition, compared to the unimanual condition. Expert dancers, in contrast, did not show this change in proprioceptive position sense after bimanual movements. We suggest that bimanual movements may improve proprioception due to interhemispheric integration in controls, but not in expert dancers.

Embodiment in the aging mind

HighlightsInternal model degradation in the elderly impairs cognitive and social abilities.Sensory impairments affect age‐specific deficits in motor control and bodily attention.Spatial navigation deficits in the elderly arise from body‐related impairments.Impaired embodiment influences empathic capabilities in the elderly. &NA; Bodily awareness is a central component of human sensation, action, and cognition. The human body is subject to profound changes over the adult lifespan. We live in an aging society: the mean age of people living in industrialized countries is currently over 40 years, and further increases are expected. Nevertheless, there is a lack of comprehensive knowledge that links changes in embodiment that occur with age to neuronal mechanisms and associated sensorimotor and cognitive deficits in older adults. Here, we synthesize existing evidence and introduce the NFL Framework of Embodied Aging, which links basic neuronal (N) mechanisms of age‐related sensorimotor decline to changes in functional (F) bodily impairments, including deficits in higher‐level cognitive functions, and impairments in daily life (L). We argue that cognitive and daily life impairments associated with old age are often due to deficits in embodiment, which can partly be linked to neuronal degradation at the sensorimotor level. The framework may encourage the development of novel approaches to improve autonomous living for older adults.

Visually-Driven Maps in Area 3b

Sensory perception relies on the precise neuronal encoding of modality-specific environmental features in primary sensory cortices. Some studies have reported the penetration of signals from other modalities even into early sensory areas. So far, no comprehensive account of maps induced by “foreign sources” exists. We addressed this question using surface-based topographic mapping techniques applied to ultra-high resolution fMRI neuroimaging data, measured in female participants. We show that fine-grained finger maps in human primary somatosensory cortex, area 3b, are somatotopically activated not only during tactile mechanical stimulation, but also when viewing the same fingers being touched. Visually-induced maps were weak in amplitude, but overlapped with the stronger tactile maps tangential to the cortical sheet when finger touches were observed in both first- and third-person perspectives. However, visually-induced maps did not overlap tactile maps when the observed fingers were only approached by an object but not actually touched. Our data provide evidence that “foreign source maps” in early sensory cortices are present in the healthy human brain, that their arrangement is precise, and that their induction is feature-selective. The computations required to generate such specific responses suggest that counterflow (feedback) processing may be much more spatially specific than has been often assumed. SIGNIFICANCE STATEMENT Using ultra-high field fMRI, we provide empirical evidence that viewing touches activates topographically aligned single finger maps in human primary somatosensory cortical area 3b. This shows that “foreign source maps” in early sensory cortices are topographic, precise, and feature-selective in healthy human participants with intact sensory pathways.

Social targets improve body-based and environment-based strategies during spatial navigation

Encoding the position of another person in space is vital for everyday life. Nevertheless, little is known about the specific navigational strategies associated with encoding the position of another person in the wider spatial environment. We asked two groups of participants to learn the location of a target (person or object) during active navigation, while optic flow information, a landmark, or both optic flow information and a landmark were available in a virtual environment. Whereas optic flow information is used for body-based encoding, such as the simulation of motor movements, landmarks are used to form an abstract, disembodied representation of the environment. During testing, we passively moved participants through virtual space, and compared their abilities to correctly decide whether the non-visible target was before or behind them. Using psychometric functions and the Bayes Theorem, we show that both groups assigned similar weights to body-based and environment-based cues in the condition, where both cue types were available. However, the group who was provided with a person as target showed generally reduced position errors compared to the group who was provided with an object as target. We replicated this effect in a second study with novel participants. This indicates a social advantage in spatial encoding, with facilitated processing of both body-based and environment-based cues during spatial navigation when the position of a person is encoded. This may underlie our critical ability to make accurate distance judgments during social interactions, for example, during fight or flight responses.

The influence of vision on tactile Hebbian learning

NMDA-dependent Hebbian learning drives neuronal plasticity in different cortical areas, and across species. In the primary somatosensory cortex (S-I), Hebbian learning is induced via the persistent low-rate afferent stimulation of a small area of skin. In particular, plasticity is induced in superficial cortical layers II/III of the S-I cortex that represents the stimulated area of skin. Here, we used the model system of NMDA-dependent Hebbian learning to investigate the influence of non-afferent (visual) input on Hebbian plasticity in S-I. We induced Hebbian learning in 48 participants by applying 3 hours of tactile coactivation to the right index fingertip via small loudspeaker membranes. During coactivation, different groups viewed either touches to individual fingers, which is known to activate S-I receptive fields, touches to an object, which should not activate S-I receptive fields, or no touch at all. Our results show that coactivation significantly lowers tactile spatial discrimination thresholds at the stimulated finger post- versus pre-training across groups. However, we did not find evidence for a significant modulatory effect of visual condition on tactile spatial discrimination performance. This suggests that non-afferent (visual) signals do not interact with Hebbian learning in superficial cortical layers of S-I, but may integrate into deeper cortical layers instead.

Modelling the human cortex in three dimensions

In cognitive neuroscience, brain-behaviour relationships are usually mapped onto a 2D cortical sheet. Cortical layers are a critical but often ignored third dimension of human cortical function. Improved resolution has put us on the threshold of beginning to image human cognition in three dimensions.

How Visual Body Perception Influences Somatosensory Plasticity

The study of somatosensory plasticity offers unique insights into the neuronal mechanisms that underlie human adaptive and maladaptive plasticity. So far, little attention has been paid on the specific influence of visual body perception on somatosensory plasticity and learning in humans. Here, we review evidence on how visual body perception induces changes in the functional architecture of the somatosensory system and discuss the specific influence the social environment has on tactile plasticity and learning. We focus on studies that have been published in the areas of human cognitive and clinical neuroscience and refer to animal studies when appropriate. We discuss the therapeutic potential of socially mediated modulations of somatosensory plasticity and introduce specific paradigms to induce plastic changes under controlled conditions. This review offers a contribution to understanding the complex interactions between social perception and somatosensory learning by focusing on a novel research field: socially mediated sensory plasticity.

LISA improves statistical analysis for fMRI

One of the principal goals in functional magnetic resonance imaging (fMRI) is the detection of local activation in the human brain. However, lack of statistical power and inflated false positive rates have recently been identified as major problems in this regard. Here, we propose a non-parametric and threshold-free framework called LISA to address this demand. It uses a non-linear filter for incorporating spatial context without sacrificing spatial precision. Multiple comparison correction is achieved by controlling the false discovery rate in the filtered maps. Compared to widely used other methods, it shows a boost in statistical power and allows to find small activation areas that have previously evaded detection. The spatial sensitivity of LISA makes it especially suitable for the analysis of high-resolution fMRI data acquired at ultrahigh field (≥7 Tesla).Functional magnetic resonance imaging (fMRI) is a powerful technique for measuring human brain activity, but the statistical analysis of fMRI data can be difficult. Here, the authors introduce a new fMRI analysis tool, LISA, which provides increased statistical power compared to existing techniques.