Direct Visual Stimulation Research Articles

True and apparent optogenetic BOLDfMRI signals

PurposeOptogenetic fMRI (ofMRI) is a novel tool in neurophysiology and neuroimaging. The method is prone to light‐induced artifacts, two of which were investigated in this study.MethodsofMRI was performed in rats using two excitatory opsins (ChR2 and C1V1TT) virally transduced in somatosensory cortex or thalamus. Heat‐induced apparent BOLD activation at the site of the optical fiber and stimulation light–induced activation of the visual pathways were investigated, and control experiments for these two artifacts were established.ResultsSpecific optogenetic BOLD activation was observed with both opsins, accompanied by BOLD in the visual pathways. Unspecific heat‐induced BOLD was ruled out by a control experiment employing low‐level constant illumination in addition to pulsed optogenetic stimulation. Activation of the visual pathways was confirmed to be physiological by direct visual stimulation of the eyes and was suppressed by additional low‐level constant light to the eyes. Light inside the brain was identified as one source of the BOLD signal observed in the visual pathways.ConclusionofMRI is a method of tremendous potential, but unspecific activations in fMRI not caused by the activation of opsins must be avoided or recognized as such. The control experiments presented here allow for validating the specificity of optogenetic stimulation. Magn Reson Med 77:126–136, 2017. © 2016 Wiley Periodicals, Inc.

True and apparent optogenetic BOLD fMRI signals.

Optogenetic fMRI (ofMRI) is a novel tool in neurophysiology and neuroimaging. The method is prone to light-induced artifacts, two of which were investigated in this study. ofMRI was performed in rats using two excitatory opsins (ChR2 and C1V1TT ) virally transduced in somatosensory cortex or thalamus. Heat-induced apparent BOLD activation at the site of the optical fiber and stimulation light-induced activation of the visual pathways were investigated, and control experiments for these two artifacts were established. Specific optogenetic BOLD activation was observed with both opsins, accompanied by BOLD in the visual pathways. Unspecific heat-induced BOLD was ruled out by a control experiment employing low-level constant illumination in addition to pulsed optogenetic stimulation. Activation of the visual pathways was confirmed to be physiological by direct visual stimulation of the eyes and was suppressed by additional low-level constant light to the eyes. Light inside the brain was identified as one source of the BOLD signal observed in the visual pathways. ofMRI is a method of tremendous potential, but unspecific activations in fMRI not caused by the activation of opsins must be avoided or recognized as such. The control experiments presented here allow for validating the specificity of optogenetic stimulation. Magn Reson Med 77:126-136, 2017. © 2016 Wiley Periodicals, Inc.

The Occipital Face Area Is Causally Involved in Facial Viewpoint Perception.

Faces are among the most salient objects we encounter during our everyday activities. Moreover, we are remarkably adept at identifying people at a glance, despite the diversity of viewpoints during our social encounters. Here, we investigate the cortical mechanisms underlying this ability by focusing on effects of viewpoint symmetry, i.e., the invariance of neural responses to mirror-symmetric facial viewpoints. We did this by temporarily disrupting neural processing in the occipital face area (OFA) using transcranial magnetic stimulation. Our results demonstrate that the OFA causally contributes to judgments facial viewpoints and suggest that effects of viewpoint symmetry, previously observed using fMRI, arise from an interhemispheric integration of visual information even when only one hemisphere receives direct visual stimulation.

Illusory Motion of the Motion Aftereffect Induces Postural Sway

It remains an open question, however, whether this perception-action cycle is the result of direct visual stimulation only, or whether postural adjustments also occur when the motion of the visual stimulus is illusory. Here, we show that the latter is the case. Prolonged viewing of visual motion results in neural adaptation, and subsequent viewing of a stationary stimulus normally results in illusory motion in the opposite direction, a famous phenomenon known as the motion aftereffect (MAE; Anstis, Verstraten, & Mather, 1998). Surprisingly, this sequence of stimulation also causes postural sway in the direction consistent with the perceived illusory motion. Control test patterns that do not generate an MAE after identical adaptation do not induce sway. This suggests that the visuo-vestibular interactions that govern postural control are not influenced by visual stimulation per se, but can be modulated by an illusory motion signal (e.g., the internal neural signal responsible for the MAE).

Topography of Covert Visual Attention in Human Superior Colliculus

Experiments were performed to examine the topography of covert visual attention signals in human superior colliculus (SC), both across its surface and in its depth. We measured the retinotopic organization of SC to direct visual stimulation using a 90° wedge of moving dots that slowly rotated around fixation. Subjects (n = 5) were cued to perform a difficult speed-discrimination task in the rotating region. To measure the retinotopy of covert attention, we used a full-field array of similarly moving dots. Subjects were cued to perform the same speed-discrimination task within a 90° wedge-shaped region, and only the cue rotated around fixation. High-resolution functional magnetic resonance imaging (fMRI, 1.2 mm voxels) data were acquired throughout SC. These data were then aligned to a high-resolution T1-weighted reference volume. The SC was segmented in this volume so that the surface of the SC could be computationally modeled and to permit calculation of a depth map for laminar analysis. Retinotopic maps were obtained for both direct visual stimulation and covert attention. These maps showed a similar spatial distribution to visual stimulation maps observed in rhesus macaque and were in registration with each other. Within the depth of SC, both visual attention and stimulation produced activity primarily in the superficial and intermediate layers, but stimulation activity extended significantly more deeply than attention.

"Homeostatic and gain control mechanisms in a developmental model of orientation map formation in V1"

Event Abstract Back to Event "Homeostatic and gain control mechanisms in a developmental model of orientation map formation in V1" Numerous studies have shown that cortical neurons can self-regulate their response gain (i.e., their output in response to an input). Theoretical studies of such gain control have primarily considered single cells or small networks of neurons in the adult brain. However, gain control is likely to be particularly important during development, because the amount and distribution of input activity can change dramatically between neurogenesis and adulthood. For instance, the developing visual system at first receives intrinsically generated input, such as retinal waves or spontaneous cortical activity, and in later stages (after eye opening) receives direct visual stimulation from the environment. In this study we examine how gain control can interact with basic homeostatic mechanisms to reproduce the experimentally observed patterns of development in a large scale model of an orientation map in the primary visual cortex (V1). Using this model, we have identified a small set of mathematical rules that can reproduce the following experimentally observed phenomena: stable orientation map development (Chapman et al. J. Neurosci., 1996, 16:6443--6453), contrast independent orientation tuning (Alitto et al. J Neurophysiol., 2004 91:2797--2808), and orientation map development that is robust against changes in the levels or distributions of input activity over time (Crair et al. Science, 1998, 279:566--570). We show that the above constraints can be met by using a simple but plausible gain control mechanism at the level of the Lateral Geniculate Nucleus (LGN) or retina, plus a mechanism that maintains a constant ratio between the strength of different input types (afferent vs. feedback, and excitatory vs. inhibitory) to each individual neuron. By directly maintaining these specific interaction ratios, it is sufficient to use a simple threshold adjustment rule for each neuron, rather than the more complex intrinsic excitability adjustment rules previously designed for more abstract networks (Triesch ICANN, 2005, 65--70). This model thus highlights the benefit of studying these phenomena in neural models whose architecture is constrained by the known connectivity of neural structures (such as V1). Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). "Homeostatic and gain control mechanisms in a developmental model of orientation map formation in V1". Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.341 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 10 Feb 2009; Published Online: 10 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Feature-Based Attentional Modulations in the Absence of Direct Visual Stimulation

When faced with a crowded visual scene, observers must selectively attend to behaviorally relevant objects to avoid sensory overload. Often this selection process is guided by prior knowledge of a target-defining feature (e.g., the color red when looking for an apple), which enhances the firing rate of visual neurons that are selective for the attended feature. Here, we used functional magnetic resonance imaging and a pattern classification algorithm to predict the attentional state of human observers as they monitored a visual feature (one of two directions of motion). We find that feature-specific attention effects spread across the visual field-even to regions of the scene that do not contain a stimulus. This spread of feature-based attention to empty regions of space may facilitate the perception of behaviorally relevant stimuli by increasing sensitivity to attended features at all locations in the visual field.

Visual Topography of Human Intraparietal Sulcus

Human parietal cortex is implicated in a wide variety of sensory and cognitive functions, yet its precise organization remains unclear. Visual field maps provide a potential structural basis for descriptions of functional organization. Here, we detail the topography of a series of five maps of the contralateral visual hemifield within human posterior parietal cortex. These maps are located along the medial bank of the intraparietal sulcus (IPS) and are revealed by direct visual stimulation during functional magnetic resonance imaging, allowing these parietal regions to be routinely and reliably identified simultaneously with occipital visual areas. Two of these maps (IPS3 and IPS4) are novel, whereas two others (IPS1 and IPS2) have previously been revealed only by higher-order cognitive tasks. Area V7, a previously identified visual map, is observed to lie within posterior IPS and to share a foveal representation with IPS1. These parietal maps are reliably observed across scan sessions; however, their precise topography varies between individuals. The multimodal organization of posterior IPS mirrors this variability in visual topography, with complementary tactile activations found immediately adjacent to the visual maps both medially and laterally. These visual maps may provide a practical framework in which to characterize the functional organization of human IPS.

Correlates of motor planning and postsaccadic fixation in the macaque monkey lateral geniculate nucleus

There is significant controversy regarding the ability of the primate visual system to construct stable percepts from a never-ending stream of brief fixations and rapid saccadic eye movements. In this study, we examined the timing and occurrence of perisaccadic modulation of LGN single-unit activity in awake-behaving macaque monkeys while they made spontaneous saccades in the dark and made visually guided saccades to discrete stimuli located outside the receptive field. Our hypothesis was that the activity of LGN cells is modulated by efference copies of motor plans to produce saccadic eye movements and that this modulation depends neither on the presence of feedforward visual information nor on a corollary discharge of signals directing saccadic eye movements. On average, 25% of LGN cells demonstrated significant perisaccadic modulation. This modulation consisted of a moderate suppression of activity that began more than 100 ms prior to the initiation of a saccadic eye movement and continued beyond the termination of the saccadic eye movement. This suppression was followed by a large enhancement of activity after the eyes arrived at the next fixation. Although members of all three LGN relay cell classes (magnocellular, parvocellular, and koniocellular) demonstrated significant saccade-related suppression and enhancement of activity, more cells demonstrated postsaccadic enhancement (25%) than perisaccadic suppression (17%). In no case did the timing of the modulation coincide directly with saccade duration. The degree of modulation observed did not vary with LGN cell class, LGN receptive field center location, center sign (ON-center or OFF-center), or saccade latency or velocity. The time course of modulation did, however, vary with saccade size such that suppression was longer for longer saccades. The fact that activity from a percentage of LGN cells from all cell classes was modulated in relationship to saccadic eye movements in the absence of direct visual stimulation suggests that this modulation is a general phenomenon not tied to specific types of visual stimuli. Similarly, because the onset of the modulation preceded eye movements by more than 100 ms, it is likely that this modulation reflects higher order motor-planning rather than a corollary of mechanisms in direct control of eye movements themselves. Finally, the fact that the largest modulation is a postsaccadic enhancement of activity may suggest that perisaccadic modulations are designed more for the facilitation of visual information processing once the eyes land at a new location than for filtering unwanted visual stimuli.

Activation of striate cortex in the absence of visual stimulation: an fMRI study of synesthesia.

It has been suggested that internally generated visual perception involves the primary visual cortex V1. To test this hypothesis, a functional MRI study was conducted with a female subject with orthographic color-word synesthesia. This subject was selected as she reported clear involuntary visualization of auditorily presented verbal material. Hearing a word resulted in seeing the word in a particular color. fMRI scans were acquired while the subject performed two verbal tasks (passive listening to words and verbal fluency). Significant activity was detected in primary visual cortex, in the absence of external visual stimulation. This finding provides evidence for a role of modulatory feedback connections between associative and primary visual areas in visual experience without direct visual stimulation.

Gestures Maintain Spatial Imagery

Recent theories suggest alternatives to the commonly held belief that the sole role of gestures is to communicate meaning directly to listeners. Evidence suggests that gestures may serve a cognitive function for speakers, possibly acting as lexical primes. We observed that participants gestured more often when describing a picture from memory than when the picture was present and that gestures were not influenced by manipulating eye contact of a listener. We argue that spatial imagery serves a short-term memory function during lexical search and that gestures may help maintain spatial images. When spatial imagery is not necessary, as in conditions of direct visual stimulation, reliance on gestures is reduced or eliminated.

New methods in the diagnosis of impotence: RigiScan� penile tumescence and rigidity monitoring and diagnostic papaverine hydrochloride injection

In 26 patients with erectile impotence and 8 healthy volunteers the value of continuous monitoring of penile tumescence and rigidity by means of the RigiScan was tested. Based on history and routine screening tests the patients were divided into 3 groups of preliminary diagnosis: psychogenic (5 patients), organic (10 patients), mixed (11 patients). Real-time measurements of tumescence and rigidity were performed during direct visual stimulation and after intracorporeal injection of 80 mg papaverine hydrochloride according to a specific protocol. A total of 21 patients were monitored during sleep studies for 2 or 3 consecutive nights. The rigidity figures of the volunteers correlated well with their subjective interpretation of the erection. Evaluation of the recordings of the impotent patients enabled reclassification of the mixed group into 3 patients with mainly organic and 8 patients with mainly psychogenic impotence. RigiScan recording of penile tumescence and rigidity appears to be of great value in the diagnosis of impotent patients. Real-time monitoring during direct visual stimulation and after papaverine injection can generally replace nocturnal measurements. If the patient shows a positive response on visual sexual stimulation (VSS) alone, then his impotence is of psychogenic origin. Failing rigidity during VSS after injection indicates vascular impotence. In patients who show negative results during VSS alone, and positive response after injection or during subsequent VSS, nocturnal monitoring will differentiate between psychogenic and neurogenic impotence.

VISUAL SPACE PERCEPTION AS INFLUENCED BY UNUSUAL VESTIBULAR STIMULATION.

During flight in aircraft and spacecraft, pilots are regularly subjected to unusual force environments. These forces not only influence a variety of pressure-sensitive mechanisms but, in particular, they stimulate the vestibular mechanism of the inner ear. The latter source of information regarding spatial orientation may be in accord with information from direct visual stimulation or it may be in conflict with it. In the first case, veridical space perception may be expected, while in the second the perception is frequently nonveridical. This results in constant errors in judgment with respect to motion of visual objects and in the pilot's estimates of the objects' position. These errors, referred to by pilots as “vertigo,” are believed to be of importance in piloting aircraft and spacecraft where the pilot's task involves actions based on visual space perception.

Evidence for Direct Stimulation of the Mammalian Nervous System with Ionizing Radiation

Exposure to x-rays of low intensity immediately arouses the sleeping rat. Activation of the central nervous system, indicated by behavioral and heart rate responses, depends upon the rat but not the dose of exposure. The arousal reaction is not dependent upon direct visual stimulation. The nervous system is probably directly sensitive to ionizing radiation.