Evolution amplified processing with temporally dispersed slow neuronal connectivity in primates

The corpus callosum (CC) provides the main route of communication between the 2 hemispheres of the brain. In monkeys, chimpanzees, and humans, callosal axons of distinct size interconnect functionally different cortical areas. Thinner axons in the genu and in the posterior body of the CC interconnect the prefrontal and parietal areas, respectively, and thicker axons in the midbody and in the splenium interconnect primary motor, somatosensory, and visual areas. At all locations, axon diameter, and hence its conduction velocity, increases slightly in the chimpanzee compared with the macaque because of an increased number of large axons but not between the chimpanzee and man. This, together with the longer connections in larger brains, doubles the expected conduction delays between the hemispheres, from macaque to man, and amplifies their range about 3-fold. These changes can have several consequences for cortical dynamics, particularly on the cycle of interhemispheric oscillators.

Visuo-vestibular mechanisms of bodily self-consciousness

Joachim Jean-Marie Forget

Bodily self-consciousness is linked to multisensory integration and is particularly dependent on vestibular perception providing the brain with the main sensory cues about body motion and location in space. Vestibular and visual inputs are permanently balanced and integrated to encode the most optimal representation of the external world and of the observer in the central nervous system. Vection, an illusory self-motion experience induced only by visual stimuli, illustrates the fact that the visual and the vestibular systems share common neural underpinnings and a similar phenomenology. Optokinetic stimulation inducing vection and direct vestibular stimulation induce whole-body motion sensations that can be used to explore multisensory interactions. A failure in visuo-vestibular integration, artificially induced by the methods of cognitive psychology or in pathological conditions, has also been reported to altered own body perception and bodily self-consciousness. The respective contributions of the vestibular and visual systems to bodily self-consciousness amongst other polymodal sensory mechanisms, and the neural correlates of visuo-vestibular convergence, should be better understood. We first performed a neuroimaging study of brain regions where optokinetic and vestibular stimuli converge, using 7T functional magnetic resonance imaging in individual subjects. We identified three main regions of convergence: (1) the depth of supramarginal gyrus or retroinsular cortex, (2) the surface of supramarginal gyrus at the temporo-parietal junction, (3) and the posterior part of middle temporal gyrus and superior temporal sulcus. Then, we aimed to induce the embodiment of an external fake rubber hand through visuo-tactile conflict - the so-called rubber hand illusion paradigm, and studied how this integration is modulated by vection. Subjects experiencing vection in the direction of the rubber hand mislocalised the position of their real hand towards the rubber hand indicating that visuo-vestibular stimuli can enhance visuo-tactile integration. We also investigated if visuo-proprioceptive and tactile integration in peripersonal space could be dynamically updated based on the congruency of visual and proprioceptive feedback. A pair of rubber hands or feet provided visual feedback. Fake and real limbs were crossed or uncrossed. We showed that sensory cues were integrated in peripersonal space, dynamically reshaped but only for hands. Finally, we investigated a rare case of an illusory own body perception in an epileptic patient suffering from multiple daily disembodiments during seizures. Seizures were associated to a focal cortical microdysplasia juxtaposed to a developmental venous anomaly in the left angular gyrus, a brain region known to be important for visuo-vestibular integration and bodily self-consciousness. Our results characterize the inferior parietal lobule as a crucial structure in merging visual, vestibular, tactile and proprioceptive inputs, allowing the emergence of the global and unified experience of being âI.â Multisensory body representation can be reshaped transiently using visual and vestibular signals or in relation to a medical condition affecting the temporo-parietal junction. The integration of visual and vestibular signals, aims to adapt dynamically our internal representations to constant changes occurring in our environment.

EPFL2015

Optical sensory and motor mapping of mouse dorsal cortex

Matthieu Pierre Auffret

Throughout species, including mice and humans, we all have to make decisions to fulfill our fundamentals needs: eat, drink, explore, communicate, reproduce... To make those decisions, we have to collect informations from the surrounding world and to process them with our nervous system. The neocortex is the most distinctive feature of the brain as it is the substrate of high cognitive functions. One commonly used model to study the brain is the mouse. Mice can be genetically modified to express fluorescent reporters, or optogenetic actuators in their neurons. The questions I ask in this thesis are where and when specific sensory information is processed in the mouse cortex, and where and when these signals are integrated to generate to a motor command. First, I developed a protocol to get reliable sensory maps from wide-field optical intrinsic signal imaging. Mice undergo a surgical procedure to get a relatively transparent view of the left dorsal cortex. Then I sequentially repetitively stimulated different parts of the body of anesthetized mice to map the cortical sensory representation of each stimulated organ. I also successfully imaged optogenetically evoked responses by combining optogenetic experiment with wide-field optical intrinsic signal imaging. Second, I found the coordinates of the tongue/jaw primary sensory cortex tjS1 and of the tongue/jaw primary motor cortex tjM1. While I was mechanically stimulating tongue and jaw in anesthetized Thy1-GCaMP6f mice, I imaged the calcium signals evoked in the left cortical hemisphere with a wide-field fluorescence macroscope. Third, I recorded cortical activity of behaving mice performing a 2-whisker discrimination task with the wide-field calcium imaging technique. There was a large difference between hit and miss trials. The amplitude of the responses in S1, S2, M1 and M2 were decreasing over the days of training. The earliest difference between hit and miss response occurred in S1 and S2 after 100 ms. Then the signals converged toward M2 where the amplitude of the response was amplified to lead to a lick command. Finally, I optogenetically stimulated the cortex of awake mice and I measured the evoked whisker movements to obtain whisker motor maps. I found that almost the entire cortex can evoke whisker movement. The earliest evoked movement occurred when S1 was stimulated, the contralateral whisker had a prolonged retraction. Then the ipsilateral whisker started large rhythmic protractions. When M1 was stimulated, it triggered the most protracted whisker movement of rhythmic protractions. The largest oscillating protraction was observed when the parietal association area (PtA) was stimulated. These data suggest that neuronal information needed to perform even simple tasks requires distributed cortical areas to process sensory inputs, like passive whisker deflection or optogenetic stimulation, and in return generate motor outputs, like licking or whisking. Future experiments must investigate the complex neuronal circuits connecting specific cell- types in various cortical regions using wide-field calcium imaging and combine it with optogenetic manipulations of this network at specific times and brain regions.

EPFL2018

(Un)crowding modulates recurrent connectivity in the visual cortex

Vitaly Chicherov, Michael Herzog, Maya Anna Jastrzebowska

Introduction: In crowding, neighboring elements impede the perception of a target. Surprisingly, increasing the number of neighboring elements can decrease crowding, i.e., lead to uncrowding (Manassi et al., 2015). Few neuroimaging studies have explored the neural correlates of crowding (Bi et al., 2009; Anderson et al., 2012; Millin et al., 2013; Chen et al., 2014; Chicherov et al., 2014; Ronconi et al., 2016). The resulting evidence about the neural locus of crowding has been equivocal, but crowding is consistently found to attenuate the BOLD response. Here, we used fMRI to investigate the effects of uncrowding on the BOLD response and effective connectivity in the visual cortex. We expected that the percent BOLD signal change (PSC) would best reflect behavioral differences related to (un)crowding in the brain areas driving the crowding effect. We used dynamic causal modelling (DCM; Friston, 2003) to investigate whether (un)crowding is rather a top-down, bottom-up or recurrent processing phenomenon. In accordance with the notion that crowding depends on grouping, we hypothesized that PSC in higher visual areas would better reflect (un)crowding and that effective connectivity would reflect the involvement of top-down processing in uncrowding. Methods: The fMRI experiment consisted of seven conditions: (1) target only (eight circular oblique target gratings surrounding a central fixation dot, tilted either clockwise (CW) or counterclockwise (CCW), (2) 2-flanker (each of the 8 targets was flanked by an inside and outside vertical grating), (3) 4-flanker (one inside and three outside flanker gratings), (4) annulus-flanker (inside and outside flankers connected into annuli), and (5-7) control conditions corresponding to conditions (2-4) with targets removed. Ten participants were asked to indicate whether target gratings were tilted CW or CCW by pushing one of two buttons or to push a button randomly if targets were not present. We calculated the PSC for each participant, each target region of interest (tg-ROI; target-activated areas in V1–V4 and LOC) and each of the conditions of interest and then correlated PSC with response accuracy. We estimated the effective connectivity between tg-ROIs using bilinear DCM and constructed a group-level parametric empirical Bayesian (PEB) model (Friston et al., 2016) over all the participants. After conducting a search over nested models and computing a Bayesian model average (BMA), we compared input-modulatory connectivity (DCM.B matrix) between crowding conditions in terms of excitatory and inhibitory bottom-up and top-down connectivity. Results: Target discrimination (accuracy) was highest in the single target condition, followed by annulus-flanker, 4-flanker and 2-flanker, respectively. A linear mixed model of PSC revealed significant main effects of condition (F(3,171) = 100.06, p

2019