Biology subjects

Weisz, N.

Publications and source records attributed to Weisz, N..

6 recordsLinked to original sources

bioRxiv2018

Pre-stimulus feedback connectivity biases the content of visual experiences

Ongoing, spontaneous fluctuations in neural excitability and in network-wide activity patterns before stimulus onset have been proposed to underlie variability in near-threshold stimulus detection paradigms, i.e. whether an object is perceived or not. Here, we investigated the impact of pre-stimulus neural fluctuations on the content of perception, i.e. whether one or another object is perceived. We recorded neural activity with magnetoencephalography before and while participants briefly viewed a bi-stable image, the Rubin face/vase illusion, and required them to report their perceived interpretation on each trial. Using multi-variate pattern analysis, we showed robust decoding of the perceptual report during the post-stimulus period. Applying source localization to the classifier weights suggested early recruitment of V1 and ~160 ms recruitment of category-sensitive FFA. These post-stimulus effects were driven by stronger oscillatory power in the gamma frequency band for face vs vase reports. In pre-stimulus intervals, we found no differences in oscillatory power between face vs. vase reports in V1 nor in FFA, indicating similar levels of neural excitability. Despite this, we found stronger connectivity between V1 and FFA prior to face reports for low-frequency oscillations. Specifically, the strength of pre-stimulus feedback connectivity (i.e. Granger causality) from FFA to V1 predicted not only the category of the upcoming percept, but also the strength of post-stimulus neural activity associated with the percept. Our work identifies pre-stimulus network states that shape future processing in category-sensitive brain regions and in this way determine the content of visual experiences.

neuroscience↗

bioRxiv2018

Prediction-related neural activity during silent periods is sharply tuned

Prior experience shapes sensory perception by enabling the formation of expectations with regards to the occurrence of upcoming sensory events. Especially in the visual modality, an increasing number of studies show that prediction-related neural signals carry feature-specific information about the stimulus. This is less established in the auditory modality, in particular without bottom-up signals driving neural activity. We studied whether auditory predictions are sharply tuned to even carry tonotopic specific information. For this purpose, we conducted a Magnetoencephalography (MEG) experiment in which participants passively listened to sound sequences that varied in their regularity (i.e. entropy). Sound presentations were temporally predictable (3 Hz rate), but were occasionally omitted. Training classifiers on the random (high entropy) sound sequence and applying them to all conditions in a time-generalized manner, allowed us to assess whether and how carrier frequency specific information in the MEG signal is modulated according to the entropy level. We show that especially in an ordered (most predictable) sensory context neural activity during the anticipatory and omission periods contains carrier-frequency specific information. Overall our results illustrate in the human auditory system that prediction-related neural activity can be tuned in a tonotopically specific manner.

neuroscience↗

bioRxiv2018

Visual cortical entrainment to unheard acoustic speech reflects intelligibility of lip movements and is mediated by dorsal stream regions

Successful lip reading requires a mapping from visual to phonological information [1]. Recently, visual and motor cortices have been implicated in tracking lip movements (e.g. [2]). It remains unclear, however, whether visuo-phonological mapping occurs already at the level of the visual cortex, that is, whether this structure tracks the acoustic signal in a functionally relevant manner. In order to elucidate this, we investigated how the cortex tracks (i.e. entrains) absent acoustic speech signals carried by silent lip movements. Crucially, we contrasted the entrainment to unheard forward (intelligible) and backward (unintelligible) acoustic speech. We observed that the visual cortex exhibited stronger entrainment to the unheard forward acoustic speech envelope compared to the unheard backward acoustic speech envelope. Supporting the notion of a visuo-phonological mapping process, this forward-backward difference of occipital entrainment was not present for actually observed lip movements. Importantly, the respective occipital region received more top-down input especially from left premotor, primary motor, somatosensory regions and, to a lesser extent, also from posterior temporal cortex. Strikingly, across participants, the extent of top-down modulation of visual cortex stemming from these regions partially correlates with the strength of entrainment to absent acoustic forward speech envelope but not to present forward lip movements. Our findings demonstrate that a distributed cortical network, including key dorsal stream auditory regions [3-5], influence how the visual cortex shows sensitivity to the intelligibility of speech while tracking silent lip movements.\n\nHighlightsO_LIVisual cortex tracks better forward than backward unheard acoustic speech envelope\nC_LIO_LIEffects not \"trivially\" caused by correlation of visual with acoustic signal\nC_LIO_LIStronger top-down control of visual cortex during forward display of lip movements\nC_LIO_LITop-down influence correlates with visual cortical entrainment effect\nC_LIO_LIResults seem to reflect visuo-phonological mapping processes\nC_LI

neuroscience↗

bioRxiv2017

Local network-level integration mediates effects of transcranial Alternating Current Stimulation

Transcranial alternating current stimulation (tACS) has been proposed as a tool to draw causal inferences on the role of oscillatory activity in cognitive functioning and has the potential to induce long-term changes in cerebral networks. However, the mechanisms of action of tACS are not yet clear, though previous modeling works have suggested that variability may be mediated by local and network-level brain states. We used magnetoencephalography (MEG) to record brain activity from 17 healthy participants as they kept their eyes open (EO) or closed (EC) while being stimulated either with sham, weak, or strong alpha-tACS using a montage commonly assumed to target occipital areas. We reconstructed the activity of sources in all stimulation conditions by means of beamforming. The analysis of resting-state data revealed an interaction of the external stimulation with the endogenous alpha power difference between EO and EC in the posterior cingulate. This region is remote from occipital cortex, which showed strongest EC vs. EO alpha modulation, thus suggesting state-dependency long-range effects of tACS. In a follow-up analysis of this online-tACS effect, we find evidence that this dependency effect could be mediated by functional network changes: connection strength from the precuneus, a region adjusting for a measure of network integration in the two states (EC vs. EO during no-tACS), was significantly correlated with the state-dependency effect in the posterior cingulate (during tACS). No analogous correlation could be found for alpha power modulations in occipital cortex. Altogether, this is the first strong evidence to illustrate how functional network architectures can shape tACS effects.

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bioRxiv2017

Decoding across sensory modalities reveals common supramodal signatures of conscious perception

An increasing number of studies highlight common brain regions and processes in mediating conscious sensory experience. While most studies have been performed in the visual modality, it is implicitly assumed that similar processes are involved in other sensory modalities. However, the existence of supramodal neural processes related to conscious perception has not been convincingly shown so far. Here, we aim to directly address this issue by investigating whether neural correlates of conscious perception in one modality can predict conscious perception in a different modality. In two separate experiments, we presented participants with successive blocks of near-threshold tasks involving tactile, visual or auditory stimuli during the same magnetoencephalography (MEG) acquisition. Using decoding analysis in the post-stimulus period between sensory modalities, our first experiment uncovered supramodal spatio-temporal neural activity patterns predicting conscious perception of the feeble stimulation. Strikingly, these supramodal patterns included activity in primary sensory regions not directly relevant to the task (e.g. neural activity in visual cortex predicting conscious perception of auditory near-threshold stimulation). We carefully replicate our results in a control experiment that furthermore show that the relevant patterns are independent of the type of report (i.e. whether conscious perception was reported by pressing or withholding a button-press). Using standard paradigms for probing neural correlates of conscious perception, our findings reveal a common signature of conscious access across sensory modalities and illustrate the temporally late and widespread broadcasting of neural representations, even into task-unrelated primary sensory processing regions.

neuroscience↗

bioRxiv2017

Rubin-vase percept is predicted by prestimulus coupling of category-sensitive occipital regions with frontal cortex

Fluctuations in what an observer perceives can be demonstrated in images that give rise to competing percepts, examples include binocular rivalry, figure-ground illusions, and other phenomena. These stimuli are an important and well-studied stimulus set in studying human conscious perception.\n\nOne such stimulus is the Rubins vase illusion, a bistable stimulus that gives rise to the perception of a vase, or the profile of two faces (hereafter referred to as the facevase stimulus). Research using this stimulus has predominately focused on the neural response whilst viewing it (Andrews et al., 2002; Hasson et al., 2001; Kleinschmidt et al., 1998). An explanation for the phenomenological switch could exist in distinct features of the on-going brain activity, Hesselmann, Kell, Eger, & Kleinschmidt (2008) showed that fluctuating BOLD levels in Fusiform Face Area (FFA) prior to presentation of the face-va ...

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