The effects of fixational eye movements on population responses in V1.: Keynote at the 20th European Conference on Eye Movements in Alicante, September 22, 2019

Video stream: https://vimeo.com/362367119 During visual fixation, the eyes make small and fast movements known as microsaccades (MSs). The effects of MSs on neural activity in the visual cortex are not well understood. Utilizing voltage-sensitive dye imaging, we imaged the spatiotemporal patterns of neuronal responses induced by MSs in early visual cortices of behaving monkeys. Our results reveal a continuous “visual instability” during fixation: while the visual stimulus moves over the retina with each MS, the neuronal activity in V1 ‘hops’ within the retinotopic map, as dictated by the MS parameters. Neuronal modulations induced by MSs are characterized by neural suppression followed by neural enhancement and increased synchronization. The suppressed activity may underlie the suppressed perception during MSs whereas the late enhancement may facilitate the processing of new incoming image information. Moreover, the instability induced by MSs applies also to neural correlates of visual perception processes such as figure-ground (FG) segregation, which appear to develop faster after fixational saccades

Spatio-temporal activation patterns of neuronal population evoked by optostimulation and the comparison to electrical microstimulation

Abstract Optostimulation and electrical microstimulation are well-established techniques that enable to artificially stimulate the brain. While the activation patterns evoked by microstimulation in cortical network are well characterized, much less is known for optostimulation. Specifically, the activation maps of neuronal population at the membrane potential level and direct measurements of these maps were barely reported. In addition, only a few studies compared the activation patterns evoked by microstimulation and optostimulation. In this study we addressed these issues by applying optostimulation in the barrel cortex of anesthetized rats after a short (ShortExp) or a long (LongExp) opsin expression time and compared it to microstimulation. We measured the membrane potential of neuronal populations at high spatial (meso-scale) and temporal resolution using voltage-sensitive dye imaging. Longer optostimulation pulses evoked higher neural responses spreading over larger region relative to short pulses. Interestingly, similar optostimulation pulses evoked stronger and more prolonged population response in the LongExp vs. the ShortExp condition. Finally, the spatial activation patterns evoked in the LongExp condition showed an intermediate state, with higher resemblance to the microstimulation at the stimulation site. Therefore, short microstimulation and optostimulation can induce wide spread activation, however the effects of optostimulation depend on the opsin expression time

Computational modeling of color perception with biologically plausible spiking neural networks.

Biologically plausible computational modeling of visual perception has the potential to link high-level visual experiences to their underlying neurons' spiking dynamic. In this work, we propose a neuromorphic (brain-inspired) Spiking Neural Network (SNN)-driven model for the reconstruction of colorful images from retinal inputs. We compared our results to experimentally obtained V1 neuronal activity maps in a macaque monkey using voltage-sensitive dye imaging and used the model to demonstrate and critically explore color constancy, color assimilation, and ambiguous color perception. Our parametric implementation allows critical evaluation of visual phenomena in a single biologically plausible computational framework. It uses a parametrized combination of high and low pass image filtering and SNN-based filling-in Poisson processes to provide adequate color image perception while accounting for differences in individual perception

Scalable Classification in Large Scale Spatiotemporal Domains Applied to Voltage-Sensitive Dye Imaging

We present an approach for learning models that obtain accurate classification of large scale data objects, collected in spatiotemporal domains. The model generation is structured in three phases: pixel selection (spatial dimension reduction), spatiotemporal features extraction and feature selection. Novel techniques for the first two phases are presented, with two alternatives for the middle phase. Model generation based on the combinations of techniques from each phase is explored. The introduced methodology is applied on datasets from the Voltage-Sensitive Dye Imaging (VSDI) domain, where the generated classification models successfully decode neuronal population responses in the visual cortex of behaving animals. VSDI currently is the best technique enabling simultaneous high spatial (10,000 points) and temporal (10 ms or less) resolution imaging from neuronal population in the cortex. We demonstrate that not only our approach is scalable enough to handle computationally challenging data, but it also contributes to the neuroimaging field of study with its decoding abilities

Collinear stimuli induce local and cross-areal coherence in the visual cortex of behaving monkeys.

BACKGROUND: Collinear patterns of local visual stimuli are used to study contextual effects in the visual system. Previous studies have shown that proximal collinear flankers, unlike orthogonal, can enhance the detection of a low contrast central element. However, the direct neural interactions between cortical populations processing the individual flanker elements and the central element are largely unknown. METHODOLOGY/PRINCIPAL FINDINGS: Using voltage-sensitive dye imaging (VSDI) we imaged neural population responses in V1 and V2 areas in fixating monkeys while they were presented with collinear or orthogonal arrays of Gabor patches. We then studied the spatio-temporal interactions between neuronal populations processing individual Gabor patches in the two conditions. Time-frequency analysis of the stimulus-evoked VSDI signal showed power increase mainly in low frequencies, i.e., the alpha band (α; 7-14 Hz). Power in the α-band was more discriminative at a single trial level than other neuronal population measures. Importantly, the collinear condition showed an increased intra-areal (V1-V1 and V2-V2) and inter-areal (V1-V2) α-coherence with shorter latencies than the orthogonal condition, both before and after the removal of the stimulus contribution. α-coherence appeared between discrete neural populations processing the individual Gabor patches: the central element and the flankers. CONCLUSIONS/SIGNIFICANCE: Our findings suggest that collinear effects are mediated by synchronization in a distributed network of proximal and distant neuronal populations within and across V1 and V2