Electroencephalographic detection of synesthesia

In this paper the research on a person declaring synesthetic abilities will be presented.According to the current state of knowledge synesthesia activates additional cortical fields in the brainwhich can be found in the EEG. The research was conducted using an EGI-EEG system (ElectricalGeodesic Inc., Eugene, Oregon, USA) with the GeoSource software. GeoSource is a tool that implementsthe algorithms LAURA, LORETA and sLORETA. Using these algorithms for EEG analysis wecan determine where in the brain the source of activity is. The authors will try to answer the questionwhether the use of these tools can prove the occurrence of synesthesia

Wine tasting: a neurophysiological measure of taste and olfaction interaction in the experience

In the last years have been provided evidences of sensory–sensory connectivity and influences of one modality over primary sensory cortex of another, a phenomena called crossmodality. Typically, for the wine tasting, sommeliers in addition to the use of the gustation, by the introduction of the wine into the mouth, employ the stimulation of the olfactory system both through a direct olfactory stimulation (by the nose) and a retro-nasal pathway (inhaling air while swirling the wine around in the mouth). Aim of the present study was to investigate the reaction to the wine gustation with and without the direct olfactory contribution, through an electroencephalographic index of approach or withdrawal (AW) motivation, and an autonomic index (Emotional Index – EI), deriving from the matching of heart rate and galvanic skin response activity and considered an indicator of emotional involvement. Results showed a statistically significant increase of the EI values in correspondence of wine tasting with the olfactory component (p<0.01) in comparison to the tasting without the direct olfactory contribution, and a trend of greater approach attitude was reported for the same condition. Data suggest an interaction of the two sensory modalities influencing the emotional and the cognitive aspects of wine tasting experience in a non-expert sampl

On the Nature of Synesthesia: A Learned Association or Something Different?

Synesthesia is a phenomenon that has captivated the interest of many researchers, as it is a unique experience of the blending of the senses. The following study was conducted in an effort to understand whether synesthetic experiences can be learned, as Bor, Rothen, Schwartzman, Clayton, & Seth (2014) claimed. While there has been much research demonstrating that synesthesia is more common in the population than previously thought, and likely to develop in young children as a learning mechanism (Watson et al., 2017a), there have not been as many event-related brain potential (ERP) studies conducted on synesthesia. ERP studies are important for synesthesia, since neural phenomena are often best measured through brain monitoring technologies, such as magneto/electroencephalography (MEG/EEG), ERP, functional Magnetic Resonance Imaging (fMRI). The current study utilizes the measurement of continuous neural data through a pre- and post-test ERP study monitoring changes occurring at the Pz electrode site for the visual N100, auditory N100, and the P300 ERP components in 15 neurotypical, non-synesthetic college-age adults. The goal of this study was to understand whether non-synesthetes can have a synesthetic experience or are merely forming a learned association after 4 weeks of grapheme-color task, and chromesthesia task training. The results show that while participants can be trained to form learned associations between letters and colors, and sounds and color as shown by a significantly reduced P300 amplitude, they do not seem to have synesthetic experiences as was previously indicated—as demonstrated by the nonsignificant change in both N100 components

The brain's response to pleasant touch: an EEG investigation of tactile caressing

Somatosensation as a proximal sense can have a strong impact on our attitude toward physical objects and other human beings. However, relatively little is known about how hedonic valence of touch is processed at the cortical level. Here we investigated the electrophysiological correlates of affective tactile sensation during caressing of the right forearm with pleasant and unpleasant textile fabrics. We show dissociation between more physically driven differential brain responses to the different fabrics in early somatosensory cortex - the well-known mu-suppression (10-20 Hz) - and a beta-band response (25-30 Hz) in presumably higher-order somatosensory areas in the right hemisphere that correlated well with the subjective valence of tactile caressing. Importantly, when using single trial classification techniques, beta-power significantly distinguished between pleasant and unpleasant stimulation on a single trial basis with high accuracy. Our results therefore suggest a dissociation of the sensory and affective aspects of touch in the somatosensory system and may provide features that may be used for single trial decoding of affective mental states from simple electroencephalographic measurements

Intrinsic functional brain networks in health and disease

6 Introduction   6  6.1   Imaging  cognitive  processes  with  functional  magnetic  resonance  imaging   7  6.2   Imaging  the  brain’s  resting  state   8  6.3   Intrinsic  connectivity  networks  in  the  resting  state   9  6.4   Investigating  modulations  and  plasticity  of  intrinsic  connectivity  networks   12 7 Paper  1:   Towards  discovery  science  of  human  brain  function  (PNAS  2010)   14 8 Paper  2:   Repeated  pain  induces  adaptations  of  intrinsic  brain  activity  to  reflect  past  and  predict future pain  (Neuroimage  2011)   30 9 Paper  3:   Intrinsic  network  connectivity  reflects  consistency  of  synesthetic  experience

General Anesthetic Conditions Induce Network Synchrony and Disrupt Sensory Processing in the Cortex

General anesthetics are commonly used in animal models to study how sensory signals are represented in the brain. Here, we used two-photon (2P) calcium activity imaging with cellular resolution to investigate how neuronal activity in layer 2/3 of the mouse barrel cortex is modified under the influence of different concentrations of chemically distinct general anesthetics. Our results show that a high isoflurane dose induces synchrony in local neuronal networks and these cortical activity patterns closely resemble those observed in EEG recordings under deep anesthesia. Moreover, ketamine and urethane also induced similar activity patterns. While investigating the effects of deep isoflurane anesthesia on whisker and auditory evoked responses in the barrel cortex, we found that dedicated spatial regions for sensory signal processing become disrupted. We propose that our isoflurane-2P imaging paradigm can serve as an attractive model system to dissect cellular and molecular mechanisms that induce the anesthetic state, and it might also provide important insight into sleep-like brain states and consciousness

Coordinated neural, behavioral, and phenomenological changes in perceptual plasticity through overtraining of synesthetic associations.

Synesthesia is associated with additional perceptual experiences, which are automatically and consistently triggered by specific inducing stimuli. Synesthesia is also accompanied by more general sensory and cortical changes, including enhanced modality-specific cortical excitability. Extensive cognitive training has been shown to generate synesthesia-like phenomenology but whether these experiences are accompanied by neurophysiological changes characteristic of synesthesia remains unknown. Addressing this question provides a unique opportunity to elucidate the neural basis of perceptual plasticity relevant to conscious experiences. Here we investigate whether extensive training of letter-color associations leads not only to synesthetic experiences, but also to changes in cortical excitability. We confirm that overtraining synesthetic associations results in synesthetic phenomenology. Stroop tasks further reveal synesthesia-like performance following training. Electroencephalography and transcranial magnetic stimulation show, respectively, enhanced visual evoked potentials (in response to untrained patterns) and lower phosphene thresholds, demonstrating specific cortical changes. An active (using letter-symbol training) and a passive control confirmed these results were due to letter-color training and not simply to repeated testing. Summarizing, we demonstrate specific cortical changes, following training-induced acquisition of synesthetic phenomenology that are characteristic of genuine synesthesia. Collectively, our data reveal dramatic plasticity in human visual perception, expressed through a coordinated set of behavioral, neurophysiological, and phenomenological changes.This work was supported by the Dr. Mortimer and Theresa Sackler Foundation, which supports the Sackler Centre for Consciousness Science, by the Swiss National Science Foundation (Grant Number PZ00P1_154954), which supports Nicolas Rothen, and by the Daphne Jackson Trust and the Biotechnology and Biological Sciences Research Council (BBSRC), which supports Daniel Bor

When the Sun Prickles Your Nose: An EEG Study Identifying Neural Bases of Photic Sneezing

BACKGROUND: Exposure to bright light such as sunlight elicits a sneeze or prickling sensation in about one of every four individuals. This study presents the first scientific examination of this phenomenon, called 'the photic sneeze reflex'. METHODOLOGY AND PRINCIPAL FINDINGS: In the present experiment, 'photic sneezers' and controls were exposed to a standard checkerboard stimulus (block 1) and bright flashing lights (block 2) while their EEG (electro-encephalogram) was recorded. Remarkably, we found a generally enhanced excitability of the visual cortex (mainly in the cuneus) to visual stimuli in 'photic sneezers' compared with control subjects. In addition, a stronger prickling sensation in the nose of photic sneezers was found to be associated with activation in the insula and stronger activation in the secondary somatosensory cortex. CONCLUSION: We propose that the photic sneeze phenomenon might be the consequence of higher sensitivity to visual stimuli in the visual cortex and of co-activation of somatosensory areas. The 'photic sneeze reflex' is therefore not a classical reflex that occurs only at a brainstem or spinal cord level but, in stark contrast to many theories, involves also specific cortical areas

Investigating the Neural Mechanisms of Unconscious and Illusory Touch Perception

Despite our everyday reliance on touch, from manipulating tools to dressing ourselves, relatively little is known about the neural correlates of tactile perception. As with other modalities, our conscious, reportable experiences of touch can dissociate from the physical tactile stimulation processed by the skin. In unconscious touch perception, tactile stimuli can be processed and guide our behavior without an accompanying conscious percept. For example, we may swat away a mosquito without having consciously registered its presence on our skin. In tactile illusions, conscious tactile experiences occur without a corresponding tactile stimulus. Multisensory tactile illusions arise when stimulation of a different modality influences conscious tactile perception. Using converging neuroscientific methods, we characterized the neural mechanisms underlying these two types of dissociations in touch perception. In a first experiment, we assessed the role of primary somatosensory cortex (S1) in conscious and unconscious touch perception using transcranial magnetic stimulation (TMS). We demonstrated for the very first time the existence of TMS-induced numbsense, whereby the disruption of S1 suppressed tactile awareness but left unconscious localization of touch above-chance. In a second experiment, we assessed the role of early somatosensory activity in a visually induced tactile illusion. We recorded electroencephalographic (EEG) activity and fast-signal optical imaging over the somatosensory cortex and found activations in S1 and S2 starting 128 ms after visual stimulus presentation associated with this illusion. These findings imply the involvement of early somatosensory representations in a multisensory illusion of touch. In a follow-up experiment, we explored the roles of S1 and of the PPC, a multimodal structure known to participate in the integration of visual and tactile signals, in this visually induced tactile illusion. Unexpectedly, stimulating S1 did not reduce visually induced tactile illusions, suggesting that these may rely on other somatosensory processes that can compensate for S1 suppression. Stimulating the PPC 140 ms after visual stimulus presentation caused a significant decrease in the visual facilitation of tactile sensitivity, likely due to an increase in visually induced tactile illusions. This demonstrated the role of the PPC in improving tactile sensitivity during visual tactile multisensory integration, and suggests it may also influence visually induced tactile illusions. In our last experiment, we used a psychophysical approach to understanding the behavioral mappings between auditory and tactile perception in sound-touch synesthesia, in which individuals experience consistent and reliable sound-induced tactile illusions. We found that sound frequency was strongly correlated with the location of synesthetic tactile illusions on the body, suggesting the involvement of early, somatotopically-organized somatosensory areas. Together, our results support the critical importance of early somatosensory brain areas in both unconscious and illusory touch perception, as well as in multisensory integration. These results provide an important insight into the neural mechanisms supporting the subjective aspects of touch perception