Limits of Cross-modal Plasticity? Short-term Visual Deprivation Does Not Enhance Cardiac Interoception, Thermosensation, or Tactile Spatial Acuity

In the present study, we investigated the effect of short-term visual deprivation on discriminative touch, cardiac interoception, and thermosensation by asking 64 healthy volunteers to perform four behavioral tasks. The experimental group contained 32 subjects who were blindfolded and kept in complete darkness for 110minutes, while the control group consisted of 32 volunteers who were not blindfolded but were otherwise kept under identical experimental conditions. Both groups performed the required tasks three times: before and directly after deprivation (or control) and after an additional washout period of 40minutes, in which all participants were exposed to normal light conditions. Our results showed that short-term visual deprivation had no effect on any of the senses tested. This finding suggests that short-term visual deprivation does not modulate basic bodily senses and extends this principle beyond tactile processing to the interoceptive modalities of cardiac and thermal sensations.

Study of rapid reorganization of visual neurofunctions with the resting-state functional MRI in pituitary adenoma patients with vision improvement after transsphenoidal surgery

INTRODUCTION

To investigate changes of vision-related resting-state activity in pituitary adenoma (PA) patients with visual improvement after transsphenoidal surgery.

METHODS

14 PA patients with visual improvement after surgery were enrolled. The resting-state functional MRI and neuro-ophthalmologic evaluation were performed before and after the operation. The functional connectivity (FC) of 8 seeds (the primary visual cortex (V1), the secondary visual cortex (V2), the middle temporal visual cortex (MT+), and fusiform gyrus(FG)) was evaluated. A paired t test was conducted to identify the differences between the two groups.

RESULTS

Compared with the preoperation counterparts, the PA patients with improved vision exhibited decreased FC with the V1, V2, MT+, FG in the left paracentral lobule, bilateral lingual gyrus, precentral gyrus(BA 4), right superior temporal gyrus(BA 22), left fusiform gyrus, bilateral middle occipital gyrus (BA 19), left cuneus, right inferior occipital gyrus, left superior frontal gyrus, right cuneus, left superior parietal lobule(BA 7),the medulla, right postcentral gyrus, and increased FC in the right middle frontal gyrus, left inferior parietal lobule (BA 40), left declive, right lentiform nucleus, inferior frontal gyrus, right superior frontal gyrus(BA 11), cingulate gyrus(BA 32), right putamen, right thalamus, left medial frontal gyrus, left claustrum, left superior frontal Medial, right rectal gyrus(BA 25) and right parahippocampal gyrus.

CONCLUSIONS

The results show most subareas within the visual cortex exhibit decreased functional connectivity. The functional changes in subareas within default mode network (DMN), action observation network (AON) and the multisensory system in PAs propose that vision improvement may lead to function remodeling in higher-order cortex.

Multisensory stimulation for the rehabilitation of unilateral spatial neglect

Unilateral spatial neglect (USN) is a neuropsychological syndrome, typically caused by lesions of the right hemisphere, whose features are the defective report of events occurring in the left (contralesional) side of space and the inability to orient and set up actions leftwards. Multisensory integration mechanisms, largely spared in USN patients, may temporally modulate spatial orienting. In this pilot study, the effects of an intensive audio-visual Multisensory Stimulation (MS) on USN were assessed, and compared with those of a treatment that ameliorates USN, Prismatic Adaptation (PA). Twenty USN stroke patients received a 2-week treatment (20 sessions, twice per day) of MS or PA. The effects of MS and PA were assessed by a set of neuropsychological clinical tests (target cancellation, line bisection, sentence reading, personal neglect, complex drawing) and the Catherine Bergego Scale for functional disability. Results showed that MS brought about an amelioration of USN deficits overall comparable to that induced by PA; personal neglect was improved only by MS, not by PA. The clinical gains of the MS treatment were not influenced by duration of disease and lesion volume, and they persisted up to one month post-treatment. In conclusion, MS represents a novel and promising rehabilitation procedure for USN.

Shaping the visual system: cortical and subcortical plasticity in the intact and the lesioned brain

Visual system is endowed with an incredibly complex organization composed of multiple visual pathway affording both hierarchical and parallel processing. Even if most of the visual information is conveyed by the retina to the lateral geniculate nucleus of the thalamus and then to primary visual cortex, a wealth of alternative subcortical pathways is present. This complex organization is experience dependent and retains plastic properties throughout the lifespan enabling the system with a continuous update of its functions in response to variable external needs. Changes can be induced by several factors including learning and experience but can also be promoted by the use non-invasive brain stimulation techniques. Furthermore, besides the astonishing ability of our visual system to spontaneously reorganize after injuries, we now know that the exposure to specific rehabilitative training can produce not only important functional modifications but also long-lasting changes within cortical and subcortical structures. The present review aims to update and address the current state of the art on these topics gathering studies that reported relevant modifications of visual functioning together with plastic changes within cortical and subcortical structures both in the healthy and in the lesioned visual system.

Single trial prestimulus oscillations predict perception of the sound-induced flash illusion

In the sound-induced flash illusion, auditory input affects the perception of visual stimuli with a large inter- and intraindividual variability. Crossmodal influence in this illusion has been shown to be associated with activity in visual and temporal areas. In this electroencephalography study, we investigated the relationship between oscillatory brain activity prior to stimulus presentation and subsequent perception of the illusion on the level of single trials. Using logistic regression, we modeled the perceptual outcome dependent on oscillatory power. We found that 25 Hz to 41 Hz activity over occipital electrodes from 0.17 s to 0.05 s prior to stimulus onset predicted the perception of the illusion. A t-test of power values, averaged over the significant cluster, between illusion and no-illusion trials showed higher power in illusion trials, corroborating the modeling result. We conclude that the observed power modulation predisposes the integration of audiovisual signals, providing further evidence for the governing role of prestimulus brain oscillations in multisensory perception.

Brain networks require a network-conscious psychopathological approach

In experimental psychology and neuroscience, technological advances and multisensory research have contributed to gradually dismiss a version of reductionism. Empirical results no longer support a brain model in which distinct "modules" perform discrete functions, but rather, a brain of partially overlapping networks. A similarly changed brain model is extending to psychopathology and clinical psychology, and partly accounts for the problems of reductionism.

Multisensory and Modality-Specific Influences on Adaptation to Optical Prisms

Visuo-motor adaptation to optical prisms displacing the visual scene (prism adaptation, PA) is a method used for investigating visuo-motor plasticity in healthy individuals and, in clinical settings, for the rehabilitation of unilateral spatial neglect. In the standard paradigm, the adaptation phase involves repeated pointings to visual targets, while wearing optical prisms displacing the visual scene laterally. Here we explored differences in PA, and its aftereffects (AEs), as related to the sensory modality of the target. Visual, auditory, and multisensory - audio-visual - targets in the adaptation phase were used, while participants wore prisms displacing the visual field rightward by 10°. Proprioceptive, visual, visual-proprioceptive, auditory-proprioceptive straight-ahead shifts were measured. Pointing to auditory and to audio-visual targets in the adaptation phase produces proprioceptive, visual-proprioceptive, and auditory-proprioceptive AEs, as the typical visual targets did. This finding reveals that cross-modal plasticity effects involve both the auditory and the visual modality, and their interactions (Experiment 1). Even a shortened PA phase, requiring only 24 pointings to visual and audio-visual targets (Experiment 2), is sufficient to bring about AEs, as compared to the standard 92-pointings procedure. Finally, pointings to auditory targets cause AEs, although PA with a reduced number of pointings (24) to auditory targets brings about smaller AEs, as compared to the 92-pointings procedure (Experiment 3). Together, results from the three experiments extend to the auditory modality the sensorimotor plasticity underlying the typical AEs produced by PA to visual targets. Importantly, PA to auditory targets appears characterized by less accurate pointings and error correction, suggesting that the auditory component of the PA process may be less central to the building up of the AEs, than the sensorimotor pointing activity per se. These findings highlight both the effectiveness of a reduced number of pointings for bringing about AEs, and the possibility of inducing PA with auditory targets, which may be used as a compensatory route in patients with visual deficits.

Early Cross-modal Plasticity in Adults

It is known that, after a prolonged period of visual deprivation, the adult visual cortex can be recruited for nonvisual processing, reflecting cross-modal plasticity. Here, we investigated whether cross-modal plasticity can occur at short timescales in the typical adult brain by comparing the interaction between vision and touch during binocular rivalry before and after a brief period of monocular deprivation, which strongly alters ocular balance favoring the deprived eye. While viewing dichoptically two gratings of orthogonal orientation, participants were asked to actively explore a haptic grating congruent in orientation to one of the two rivalrous stimuli. We repeated this procedure before and after 150 min of monocular deprivation. We first confirmed that haptic stimulation interacted with vision during rivalry promoting dominance of the congruent visuo-haptic stimulus and that monocular deprivation increased the deprived eye and decreased the nondeprived eye dominance. Interestingly, after deprivation, we found that the effect of touch did not change for the nondeprived eye, whereas it disappeared for the deprived eye, which was potentiated after deprivation. The absence of visuo-haptic interaction for the deprived eye lasted for over 1 hr and was not attributable to a masking induced by the stronger response of the deprived eye as confirmed by a control experiment. Taken together, our results demonstrate that the adult human visual cortex retains a high degree of cross-modal plasticity, which can occur even at very short timescales.

Dissecting neural circuits for multisensory integration and crossmodal processing

We rely on rich and complex sensory information to perceive and understand our environment. Our multisensory experience of the world depends on the brain's remarkable ability to combine signals across sensory systems. Behavioural, neurophysiological and neuroimaging experiments have established principles of multisensory integration and candidate neural mechanisms. Here we review how targeted manipulation of neural activity using invasive and non-invasive neuromodulation techniques have advanced our understanding of multisensory processing. Neuromodulation studies have provided detailed characterizations of brain networks causally involved in multisensory integration. Despite substantial progress, important questions regarding multisensory networks remain unanswered. Critically, experimental approaches will need to be combined with theory in order to understand how distributed activity across multisensory networks collectively supports perception.

Changes in the Vision-related Resting-state Network in Pituitary Adenoma Patients After Vision Improvement

Background:

The aim of this research was to investigate the changes in the vision-related resting-state network (V-RSN) in pituitary adenoma (PA) patients after vision improvement, which was induced by operative treatment.

Methods:

Ten PA patients with an improved visual acuity or/and visual field after transsphenoidal pituitary tumor resection were recruited and underwent a complete neuro-ophthalmologic evaluation, as well as an magnetic resonance imaging (MRI) protocol, including structural and resting-state functional MRI sequences before and after the operation. The regional homogeneity (ReHo) of the V-RSN was evaluated. Two sample t-test was performed to identify the significant differences in the V-RSN in the PA patients before and after transsphenoidal pituitary tumor resection.

Results:

Compared with the preoperation counterparts, the PA patients with improved vision after the operation exhibited reduced ReHo in the bilateral thalamus, globus pallidus, caudate nucleus, putamen nucleus, supplementary motor area, and left hippocampal formation, and increased ReHo in the bilateral cuneus gyrus, calcarine gyrus, right lingual gyrus, and fusiform gyrus.

Conclusions:

PA patients with improved vision exhibit increased neural activity within the visual cortex, but decreased neural activity in subareas of the multisensory and multimodal systems beyond the vision cortex.

Transcranial direct current stimulation as a tool in the study of sensory-perceptual processing

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique with increasing popularity in the fields of basic research and rehabilitation. It is an affordable and safe procedure that is beginning to be used in the clinic, and is a tool with potential to contribute to the understanding of neural mechanisms in the fields of psychology, neuroscience, and medical research. This review presents examples of investigations in the fields of perception, basic sensory processes, and sensory rehabilitation that employed tDCS. We highlight some of the most relevant efforts in this area and discuss possible limitations and gaps in contemporary tDCS research. Topics include the five senses, pain, and multimodal integration. The present work aims to present the state of the art of this field of research and to inspire future investigations of perception using tDCS.

When audiovisual correspondence disturbs visual processing

Multisensory integration is known to create a more robust and reliable perceptual representation of one's environment. Specifically, a congruent auditory input can make a visual stimulus more salient, consequently enhancing the visibility and detection of the visual target. However, it remains largely unknown whether a congruent auditory input can also impair visual processing. In the current study, we demonstrate that temporally congruent auditory input disrupts visual processing, consequently slowing down visual target detection. More importantly, this cross-modal inhibition occurs only when the contrast of visual targets is high. When the contrast of visual targets is low, enhancement of visual target detection is observed, consistent with the prediction based on the principle of inverse effectiveness (PIE) in cross-modal integration. The switch of the behavioral effect of audiovisual interaction from benefit to cost further extends the PIE to encompass the suppressive cross-modal interaction.

Tuning and disrupting the brain-modulating the McGurk illusion with electrical stimulation

In the so-called McGurk illusion, when the synchronized presentation of the visual stimulus /ga/ is paired with the auditory stimulus /ba/, people in general hear it as /da/. Multisensory integration processing underlying this illusion seems to occur within the Superior Temporal Sulcus (STS). Herein, we present evidence demonstrating that bilateral cathodal transcranial direct current stimulation (tDCS) of this area can decrease the McGurk illusion-type responses. Additionally, we show that the manipulation of this audio-visual integrated output occurs irrespective of the number of eye-fixations on the mouth of the speaker. Bilateral anodal tDCS of the Parietal Cortex also modulates the illusion, but in the opposite manner, inducing more illusion-type responses. This is the first demonstration of using non-invasive brain stimulation to modulate multisensory speech perception in an illusory context (i.e., both increasing and decreasing illusion-type responses to a verbal audio-visual integration task). These findings provide clear evidence that both the superior temporal and parietal areas contribute to multisensory integration processing related to speech perception. Specifically, STS seems fundamental for the temporal synchronization and integration of auditory and visual inputs. For its part, posterior parietal cortex (PPC) may adjust the arrival of incoming audio and visual information to STS thereby enhancing their interaction in this latter area.

Bridging the divide between sensory integration and binding theory: Using a binding-like neural synchronization mechanism to model sensory enhancements during multisensory interactions

Neural information combination problems are ubiquitous in cognitive neuroscience. Two important disciplines, although conceptually similar, take radically different approaches to these problems. Sensory binding theory is largely grounded in synchronization of neurons responding to different aspects of a stimulus, resulting in a coherent percept. Sensory integration focuses more on the influences of the senses on each other and is largely grounded in the study of neurons that respond to more than one sense. It would be desirable to bridge these disciplines, so that insights gleaned from either could be harnessed by the other. To link these two fields, we used a binding-like oscillatory synchronization mechanism to simulate neurons in rattlesnake that are driven by one sense but modulated by another. Mutual excitatory coupling produces synchronized trains of action potentials with enhanced firing rates. The same neural synchronization mechanism models the behavior of a population of cells in cat visual cortex that are modulated by auditory activation. The coupling strength of the synchronizing neurons is crucial to the outcome; a criterion of strong coupling (kept weak enough to avoid seriously distorting action potential amplitude) results in intensity-dependent sensory enhancement-the principle of inverse effectiveness-a key property of sensory integration.