Research

Selected papers

Layer-specific activation of sensory input and predictive feedback in the human primary somatosensory cortex

When humans perceive a sensation, their brains integrate inputs from sensory receptors and process them based on their expectations. The mechanisms of this predictive coding in the human somatosensory system are not fully understood. We fill a basic gap in our understanding of the predictive processing of somatosensation by examining the layer-specific activity in sensory input and predictive feedback in the human primary somatosensory cortex (S1). We acquired sub-millimeter fMRI data at 7T during a task of (a) perceived, (b) predictable, and (c) unpredictable touching sequences. We demonstrate that the sensory input from thalamic projects preferentially activate the middle layer, while the superficial and deep layers in S1 are more engaged for cortico-cortical predictive feedback input. These findings are pivotal to understanding the mechanisms of tactile prediction processing in the human somatosensory cortex.
Yu et al. (2019) Science Advances 5,eaav9053

Layer-specific activation in human primary somatosensory cortex during tactile temporal prediction error processing

The human brain continuously generates predictions of incoming sensory input and calculates corresponding prediction errors from the perceived inputs to update internal predictions. In human primary somatosensory cortex (area 3b), different cortical layers are involved in receiving the sensory input and generation of error signals. It remains unknown, however, how the layers in the human area 3b contribute to the temporal prediction error processing. To investigate prediction error representation in the area 3b across layers, we acquired layer-specific fMRI data at 7T from human area 3b during a task of index finger poking with no-delay, short-delay and long-delay touching sequences. We demonstrate that all three tasks increased activity in both superficial and deep layers of area 3b compared to the random sensory input. The fMRI signal was differentially modulated solely in the deep layers rather than the superficial layers of area 3b by the delay time. Compared with the no-delay stimuli, activity was greater in the deep layers of area 3b during the short-delay stimuli but lower during the long-delay stimuli. This difference activity features in the superficial and deep layers suggest distinct functional contributions of area 3b layers to tactile temporal prediction error processing. The functional segregation in area 3b across layers may reflect that the excitatory and inhibitory interplay in the sensory cortex contributions to flexible communication between cortical layers or between cortical areas.
Yu et al. (2022) NeuroImage 248,118867

Different activation signatures in the primary sensorimotor and higher-level regions for haptic three-dimensional curved surface exploration

Haptic object perception begins with continuous exploratory contact, and the human brain needs to accumulate sensory information continuously over time. However, it is still unclear how the primary sensorimotor cortex (PSC) interacts with these higher-level regions during haptic exploration over time. This fMRI study investigates time-dependent haptic object processing by examining brain activity during haptic 3D curve and roughness estimations. For this experiment, we designed sixteen haptic stimuli (4 kinds of curves × 4 varieties of roughness) for the haptic curve and roughness estimation tasks. Twenty participants were asked to move their right index and middle fingers along the surface twice and to estimate one of the two features—roughness or curvature—depending on the task instruction. We found that the brain activity in several higher-level regions (e.g., the bilateral posterior parietal cortex) linearly increased as the number of curves increased during the haptic exploration phase. Surprisingly, we found that the contralateral PSC was parametrically modulated by the number of curves only during the late exploration phase but not during the early exploration phase. In contrast, we found no similar parametric modulation activity patterns during the haptic roughness estimation task in either the contralateral PSC or in higher-level regions. Thus, our findings suggest that haptic 3D object perception is processed across the cortical hierarchy, whereas the contralateral PSC interacts with other higher-level regions across time in a manner that is dependent upon the features of the object.
Yang et al. (2021) NeuroImage 231,117754

Event-related potential evidence for tactile orientation processing in the human brain

It is well known that information on stimulus orientation play an important role in sensory processing. However, the neural mechanisms underlying somatosensory orientation perception are poorly understood. Adaptation has been widely used as a tool to study examine sensitivity to specific feature of sensory stimulus. Using the adaptation paradigm, we measured event-related potentials (ERPs) in response to tactile orientation stimuli presented pseudo-randomly to the right-hand palm in trials with all the same or different orientations. Twenty subjects were asked to count the tactile orientation stimuli. The results showed that the early ERP component (N60) was abated at the 9th repetition, whilst this effect was absent in different orientation session. The subsequent N120 amplitudes showed strong adaptation with a steady amplitude decrease from the first repetition, but not different orientation session. Finally, P300 amplitude was also decreased from the first stimulation in the same and different orientation sessions. Based on these findings, we propose the possible program of tactile orientation processing in the brain, which may provide a new perspective for future research. These findings would help us to understanding the mechanisms of tactile orientation processing in the human brain.
Yang et al. (2024) Experimental Brain Research 242:809–817

Tactile angle discriminability improvement: contributions of working memory training and continuous attended sensory input

Perceptual learning is commonly assumed to enhance perception through continuous attended sensory input. However, learning is generalizable to performance in untrained stimuli and tasks. Although previous studies have observed a possible generalization effect across tasks as a result of working memory (WM) training, comparisons of the contributions of WM training and continuous attended sensory input to perceptual learning generalization are still rare. Therefore, we compared which factors contributed most to perceptual generalization and investigated which skills acquired during WM training led to tactile generalization across tasks. Here, a Braille-like dot pattern matching N-back WM task was used as the WM training task, with four workload levels (0, 1, 2, and 3-back levels). A tactile angle discrimination (TAD) task was used as a pre- and posttest to assess improvements in tactile perception. Between tests, four subject groups were randomly assigned to 4 different workload N-back tasks to consecutively complete three sessions of training. The results showed that tactile N-back WM training could enhance TAD performance, with the 3-back training group having the highest TAD threshold improvement rate. Furthermore, the rate of WM capacity improvement on the 3-back level across training sessions was correlated with the rate of TAD threshold improvement. These findings suggest that continuous attended sensory input and enhanced WM capacity can lead to improvements in TAD ability, and that greater improvements in WM capacity can predict greater improvements in TAD performance.
Wang et al. (2022) Journal of Neurophysiology 127(5),1398-1406

A New Method for Haptic Shape Discriminability Detection

Touch shape discrimination has been widely used in the measurement of spatial acuity and cognition. However, few devices can well improve the efficiency of the test and reduce its time. To solve this problem, we develop an automatic haptic angle sorting device. In the device, the microcomputer integrated in the hardware of the device greatly enhances the automation, the designed appearance structure improves the automation of the device, and the developed software is more userfriendly for nonprofessionals. Instead of using timeconsuming and inefficient staircase procedures and 2AFC (two-alternative forced choice), the device was tested using the angle sorting method. To verify the effectiveness of the method, angle sorting and two angle discrimination experiments were designed, and it is found that the former takes significantly less time than the latter. In addition, there is a strong correlation between the angle sort error score and the two angle discrimination threshold, which indicates the effectiveness of the experimental results. The high efficiency and reliability of the device test also provide a convenient means to assess the haptic spatial acuity, which may have potential application value in the early diagnosis and assessment of peripheral neuropathy.
Liu et al. (2021) Applied Sciences 11(15),7049

Development of a Piezoelectric Actuated Tactile Stimulation Device for Population Receptive Field Mapping in Human Somatosensory Cortex with fMRI

We designed a multichannel piezoelectric actuated tactile stimulation device consisting of an execution unit and a control unit to generate and deliver tactile stimulation that had 2.64 mm displacement with a frequency range of 1-30 Hz. Through an output performance test and MR compatibility test, our device design could play a part in finger pRF representation characteristics in the primary somatosensory cortex. Comparing the along-digits paradigm and cross-digits paradigm designs, the activation representation showed the same order in within-dimension and between-dimension analyses. The thumb (D1) expressed larger relative volumes in the cross-digits paradigm, and in both paradigms, the index finger (D2) expressed a larger receptive field that contributed to information integration.
Wu et al. (2022) Journal of Magnetic Resonance Imaging 56,1055–1065