Biology subjects

Khademi, F.

Publications and source records attributed to Khademi, F..

5 recordsLinked to original sources

bioRxiv2023

Visual feature tuning properties of short-latency stimulus-driven ocular position drift responses during gaze fixation

Ocular position drifts during gaze fixation are generally considered to be random walks. However, we recently identified a short-latency ocular position drift response, of approximately 1 min arc amplitude, that is triggered within <100 ms by visual onsets. This systematic eye movement response is feature-tuned and seems to be coordinated with a simultaneous resetting of the saccadic system by visual stimuli. However, much remains to be learned about the drift response, especially for designing better-informed neurophysiological experiments unraveling its mechanistic substrates. Here we systematically tested multiple new feature tuning properties of drift responses. Using highly precise eye tracking in three male rhesus macaque monkeys, we found that drift responses still occur for tiny foveal visual stimuli. Moreover, the responses exhibit size tuning, scaling their amplitude as a function of stimulus size, and they also possess a monotonically increasing contrast sensitivity curve. Importantly, short-latency drift responses still occur for small peripheral visual targets, which additionally introduce spatially-directed modulations in drift trajectories towards the appearing peripheral stimuli. Drift responses also remain predominantly upward even for stimuli exclusively located in the lower visual field, and even when starting gaze position is upward. When we checked the timing of drift responses, we found that it was better synchronized to stimulus-induced saccadic inhibition timing than to stimulus onset. These results, along with a suppression of drift response amplitudes by peri-stimulus saccades, suggest that drift responses reflect the rapid impacts of short-latency and feature-tuned visual neural activity on final oculomotor control circuitry in the brain. SignificanceDuring gaze fixation, the eye drifts slowly in between microsaccades. While eye position drifts are generally considered to be random eye movements, we recently found that they are modulated with very short latencies by some stimulus onsets. Here we characterized the feature-tuning properties of such stimulus-driven drift responses. Our results demonstrate that drift eye movements are not random, and that visual stimuli can impact them in a manner similar to how such stimuli impact microsaccades.

neuroscience↗

bioRxiv2023

Visual feature tuning properties of stimulus-driven saccadic inhibition in macaque monkeys

Saccadic inhibition refers to a short-latency transient cessation of saccade generation after visual sensory transients. This oculomotor phenomenon occurs with a latency that is consistent with a rapid influence of sensory responses, such as stimulus-induced visual bursts, on oculomotor control circuitry. However, the neural mechanisms underlying saccadic inhibition are not well understood. Here, we exploited the fact that macaque monkeys experience robust saccadic inhibition to test the hypothesis that inhibition time and strength exhibit systematic visual feature tuning properties to a multitude of visual feature dimensions commonly used in vision science. We measured saccades in three monkeys actively controlling their gaze on a target, and we presented visual onset events at random times. Across six experiments, the visual onsets tested size, spatial frequency, contrast, motion direction, and motion speed dependencies of saccadic inhibition. We also investigated how inhibition might depend on the behavioral relevance of the appearing stimuli. We found that saccadic inhibition starts earlier, and is stronger, for large stimuli of low spatial frequencies and high contrasts. Moreover, saccadic inhibition timing depends on motion direction, with earlier inhibition systematically occurring for horizontally than for vertically drifting gratings. On the other hand, saccadic inhibition is stronger for faster motions, and when the appearing stimuli are subsequently foveated. Besides documenting a range of feature tuning dimensions of saccadic inhibition on the properties of exogenous visual stimuli, our results establish macaque monkeys as an ideal model system for unraveling the neural mechanisms underlying a highly ubiquitous oculomotor phenomenon in visual neuroscience. New and noteworthyVisual onsets dramatically reduce saccade generation likelihood with very short latencies. Such latencies suggest that stimulus-induced visual responses, normally jumpstarting perceptual and scene analysis processes, can also directly impact the decision of whether to generate saccades or not, causing saccadic inhibition. Consistent with this, we found that changing the appearance of the visual onsets systematically alters the properties of saccadic inhibition. These results constrain neurally-inspired models of coordination between saccade generation and exogenous sensory stimulation.

neuroscience↗

bioRxiv2022

Superior colliculus visual neural sensitivity at the lower limit of natural self-induced image displacements

Visual pattern analysis relies on computations from neurons possessing spatially confined receptive fields. Often, such receptive fields are orders of magnitude larger than the visual pattern components being processed, as well as these components minute displacements on the retina, whether due to small object or self motions. Yet, perception effortlessly handles such visual conditions. Here, we show that in the primate superior colliculus, a brain structure long associated with oculomotor control, neurons with relatively large receptive fields are still sensitive to visual pattern displacements as small as 1 min arc. We used real-time gaze-contingent retinal image stabilization to control the instantaneous spatio-temporal luminance modulation of detailed patterns experienced by neurons, probing sensitivity to the lower limit of natural self-induced image displacements. Despite a large difference between pattern displacement amplitudes and receptive field sizes, collicular neurons were strongly sensitive to the visual pattern consequences of the smallest possible image-shifting eye movements.

neuroscience↗

bioRxiv2021

Enhancement of the immunogenicity of a Mycobacterium tuberculosis fusion protein using ISCOMATRIX and PLUSCOM nano-adjuvants after nasal administration in mice

BackgroundTuberculosis (TB), a contagious disease caused by Mycobacterium tuberculosis (M. tuberculosis), remains a health problem worldwide and this infection has the highest mortality rate among bacterial infections. Current studies suggest that intranasal administration of new tuberculosis vaccines could enhance the immunogenicity of M. tuberculosis antigens. Hence, we aim to evaluate the protective efficacy and immunogenicity of HspX/EsxS fusion protein of M. tuberculosis along with ISCOMATRIX and PLUSCOM nano-adjuvants and MPLA through the intranasal administration in mice model. MethodsIn present study, the recombinant fusion protein was expressed in Escherichia coli and purified and used to prepare different nanoparticle formulations in combination with ISCOMATRIX and PLUSCOM nano-adjuvants and MPLA. Mice were intranasally vaccinated with each formulation three times at an interval of 2 weeks. Finally, IFN-{gamma}, IL-4. IL-17 and TGF-{beta} concentration in supernatant of cultured splenocytes of vaccinated mice as well as serum titers of IgG1 and IgG2a and sIgA titers in nasal lavage were determined. ResultsAccording to obtained results, intranasally vaccinated mice with formulations containing ISCOMATRIX and PLUSCOM nano-adjuvants and MPLA could effectively induced IFN-{gamma} and sIgA responses. Moreover, both HspX/EsxS/ISCOMATRIX/MPLA and HspX/EsxS/PLUSCOM/MPLA and their BCG booster formulation could strongly stimulate the immune system and enhance the immunogenicity of M. tuberculosis antigens. ConclusionThe results demonstrate the potential of HspX/EsxS-fused protein in combination with ISCOMATRIX, PLUSCOM and MPLA after nasal administration in enhancing immune response against of M. tuberculosis antigens. So, nasal immunization with these formulations, could induce immune responses and considered as new TB vaccine or as BCG booster.

microbiology↗

bioRxiv2019

Visual feature tuning of superior colliculus neural reafferent responses after fixational microsaccades

The primate superior colliculus (SC) is causally involved in microsaccade generation. Moreover, visually-responsive SC neurons across this structures topographic map, even at peripheral eccentricities much larger than the tiny microsaccade amplitudes, exhibit significant modulations of evoked response sensitivity when stimuli appear peri-microsaccadically. However, during natural viewing, visual stimuli are normally stably present in the environment and are only shifted on the retina by eye movements. Here we investigated this scenario for the case of microsaccades, asking whether and how SC neurons respond to microsaccade-induced image jitter. We recorded neural activity from two male rhesus macaque monkeys. Within the response field (RF) of a neuron, there was a stable stimulus consisting of a grating of one of three possible spatial frequencies. The grating was stable on the display, but microsaccades periodically jittered the retinotopic RF location over it. We observed clear short-latency visual reafferent responses after microsaccades. These responses were weaker, but earlier (relative to new fixation onset after microsaccade end), than responses to sudden stimulus onsets without microsaccades. The reafferent responses clearly depended on microsaccade amplitude, as well as microsaccade direction relative to grating orientation. Our results indicate that one way for microsaccades to influence vision is through modulating how the spatio-temporal landscape of SC visual neural activity represents stable stimuli in the environment. Such representation strongly depends on the specific pattern of temporal luminance modulations expected from the relative relationship between eye movement vector (size and direction), on the one hand, and spatial visual pattern layout, on the other. Significance statementDespite being diminutive, microsaccades still jitter retinal images. We investigated how such jitter affects superior colliculus (SC) activity. We found that SC neurons exhibit short-latency visual reafferent bursts after microsaccades. These bursts reflect not only the spatial luminance profiles of visual patterns, but also how such profiles are shifted by eye movement size and direction. These results indicate that the SC continuously represents visual patterns, even as they are jittered by the smallest possible saccades.

neuroscience↗