Visual Sensory Input Research Articles

The dark side of the alpha rhythm: fMRI evidence for induced alpha modulation during complete darkness

The unique role of the EEG alpha rhythm in different states of cortical activity is still debated. The main theories regarding alpha function posit either sensory processing or attention allocation as the main processes governing its modulation. Closing and opening eyes, a well-known manipulation of the alpha rhythm, could be regarded as attention allocation from inward to outward focus though during light is also accompanied by visual change. To disentangle the effects of attention allocation and sensory visual input on alpha modulation, 14 healthy subjects were asked to open and close their eyes during conditions of light and of complete darkness while simultaneous recordings of EEG and fMRI were acquired. Thus, during complete darkness the eyes-open condition is not related to visual input but only to attention allocation, allowing direct examination of its role in alpha modulation. A data-driven ridge regression classifier was applied to the EEG data in order to ascertain the contribution of the alpha rhythm to eyes-open/eyes-closed inference in both lighting conditions. Classifier results revealed significant alpha contribution during both light and dark conditions, suggesting that alpha rhythm modulation is closely linked to the change in the direction of attention regardless of the presence of visual sensory input. Furthermore, fMRI activation maps derived from an alpha modulation time-course during the complete darkness condition exhibited a right frontal cortical network associated with attention allocation. These findings support the importance of top-down processes such as attention allocation to alpha rhythm modulation, possibly as a prerequisite to its known bottom-up processing of sensory input.

Impaired integration of object knowledge and visual input in a case of ventral simultanagnosia with bilateral damage to area V4

This study examines how brain damage can affect the cognitive processes that support the integration of sensory input and prior knowledge during shape perception. It is based on the first detailed study of acquired ventral simultanagnosia, which was found in a patient (M.T.) with posterior occipitotemporal lesions encompassing V4 bilaterally. Despite showing normal object recognition for single items in both accuracy and response times (RTs), and intact low-level vision assessed across an extensive battery of tests, M.T. was impaired in object identification with overlapping figures displays. Task performance was modulated by familiarity: Unlike controls, M.T. was faster with overlapping displays of abstract shapes than with overlapping displays of common objects. His performance with overlapping common object displays was also influenced by both the semantic relatedness and visual similarity of the display items. These findings challenge claims that visual perception is driven solely by feedforward mechanisms and show how brain damage can selectively impair high-level perceptual processes supporting the integration of stored knowledge and visual sensory input.

Experimental System for Investigation of Visual Sensory Input in Postural Feedback Control

The human postural control system represents a biological feedback system responsible for maintenance of upright stance. Vestibular, proprioceptive and visual sensory inputs provide the most important information into the control system, which controls body centre of mass (COM) in order to stabilize the human body resembling an inverted pendulum. The COM can be measured indirectly by means of a force plate as the centre of pressure (COP). Clinically used measurement method is referred to as posturography. In this paper, the conventional static posturography is extended by visual stimulation, which provides insight into a role of visual information in balance control. Visual stimuli have been designed to induce body sway in four specific directions – forward, backward, left and right. Stabilograms were measured using proposed single-PC based system and processed to calculate velocity waveforms and posturographic parameters. The parameters extracted from pre-stimulus and on-stimulus periods exhibit statistically significant differences.

Reduction in sensitivity to radial optic-flow congruent with ego-motion

Visual motion, such as radial optic flow, is an important cue for perceiving direction during ego-motion. Several previous studies have reported that the perceived speed of a radial optic flow is underestimated when the represented ego-motion direction between radial optic flow and non-visual (such as vestibular or/and proprioceptive) information is congruent. In the present study, we examined whether sensitivity to different types of optic flow (radial vs. laminar) interacts with vestibular input in different ways by using another method: instead of estimating the perceived speed of the visual motion pattern, we measured motion-coherence thresholds. The results indicated that when the heading direction was represented by a radial optic-flow pattern, the radial optic-flow sensitivity was significantly lower under the condition where the visual and vestibular sensory input were congruent with the ego-motion direction than under the condition where the visuo-vestibular input and ego-motion were incongruent. These results indicated that radial optic-flow sensitivity was decreased by the congruent vestibular input during the ego-motion event. On the other hand, when the direction of ego-motion was represented by a laminar optic flow, the results were different from those observed with radial optic flows. These data suggest that vestibular input has some effect on optic-flow sensitivity but that the magnitude of the effect of vestibular input may differ between distinct flow patterns such as radial and laminar optic flows.

Visuo-haptic Neuronal Convergence Demonstrated with an Inversely Effective Pattern of BOLD Activation

We investigated the neural substrates involved in visuo-haptic neuronal convergence using an additive-factors design in combination with fMRI. Stimuli were explored under three sensory modality conditions: viewing the object through a mirror without touching (V), touching the object with eyes closed (H), or simultaneously viewing and touching the object (VH). This modality factor was crossed with a task difficulty factor, which had two levels. On the basis of an idea similar to the principle of inverse effectiveness, we predicted that increasing difficulty would increase the relative level of multisensory gain in brain regions where visual and haptic sensory inputs converged. An ROI analysis focused on the lateral occipital tactile-visual area found evidence of inverse effectiveness in the left lateral occipital tactile-visual area, but not in the right. A whole-brain analysis also found evidence for the same pattern in the anterior aspect of the intraparietal sulcus, the premotor cortex, and the posterior insula, all in the left hemisphere. In conclusion, this study is the first to demonstrate visuo-haptic neuronal convergence based on an inversely effective pattern of brain activation.

Migraine, motion sensitivity, and temporal binding

Little is known about vestibular-related timing processes in patients with disequilibrium. Patients with a history of migraine headaches often complain of significant motion sensitivity and long-term vague imbalance inconsistent with a peripheral vestibular disorder. Some of these people have episodic spells of severe vertigo termed ‘vestibular migraines’. Other patients have no history of migraine but do report significant motion sensitivity. Motion sensitivity has typically been explained as a mismatch between the amplitude of vestibular and other (typically visual) sensory inputs. Another possibility is that motion sensitive patients may suffer from a mismatch in the temporal integration of vestibular and other sensory inputs. Here, we compared the temporal binding window (TBW) of vestibular + auditory stimuli in normal subjects, subjects with motion sensitivity, and those with both migraine and motion sensitivity. We asked subjects undergoing earth-vertical sinusoidal rotations at 0.5 Hz, 128°/s to identify whether a metronome-like series of tone bursts was synchronous with their cyclic motion. We calculated the TBW as the range in time encompassing the middle 68% of the area under the psychometric curve. The TBW in normal subjects was 312 ± 135 ms (mean ± SD), in subjects with motion sensitivity was 454 ± 103 ms, and in subjects with migraine and motion sensitivity was 451 ± 124 ms. The TBW of normal subjects was significantly shorter than the other groups. Temporal errors in perception, as manifested by a prolongation of the TBW, are a plausible mechanism for imbalance in patients with migraine and motion sensitivity.

Interactions between Senses: Updating on Neural Mechanisms and Behavioral Evidence

Interactions between Senses: Updating on Neural Mechanisms and Behavioral Evidence

Functional connectivity in cortical regions in dementia with Lewy bodies and Alzheimer's disease

Using resting-state functional magnetic resonance imaging, spontaneous low-frequency fluctuations in the blood oxygenation level-dependent signal were measured to investigate connectivity between key brain regions hypothesized to be differentially affected in dementia with Lewy bodies compared with Alzheimer's disease and healthy controls. These included connections of the hippocampus, because of its role in learning, and parietal and occipital areas involved in memory, attention and visual processing. Connectivity was investigated in 47 subjects aged 60 years and over: 15 subjects with dementia with Lewy bodies, 16 subjects with Alzheimer's disease and 16 control subjects. Subjects were scanned using a 3 Tesla magnetic resonance imaging system. The mean blood oxygenation level-dependent signal time series was extracted from seed regions in the hippocampus, posterior cingulate cortex, precuneus and primary visual cortex and correlated with all other brain voxels to determine functional connectivity. Both subjects with dementia with Lewy bodies and Alzheimer's disease showed greater connectivity than control subjects. Compared with controls, the dementia with Lewy bodies group had greater connectivity between the right posterior cingulate cortex and other brain areas. In dementia with Lewy bodies, there were no significant differences in hippocampal connectivity compared with controls, but in Alzheimer's disease left hippocampal connectivity was greater compared with controls. There were no significant differences between groups for precuneus or primary visual cortex connectivity. No seed regions showed significantly less connectivity in subjects with dementia with Lewy bodies or Alzheimer's disease compared with controls. We found greater connectivity with the posterior cingulate in dementia with Lewy bodies and with the hippocampus in Alzheimer's disease. Consistent with the known relative preservation of memory in dementia with Lewy bodies compared with Alzheimer's disease, hippocampal connectivity was not found to be greater in dementia with Lewy bodies. Importantly, while metabolic imaging shows functional change in primary visual cortex in dementia with Lewy bodies, which is hypothesized to account for visual hallucinations, we found connectivity with this region to be unaffected. This implicates areas beyond visual sensory input level in the visual symptoms and visual–perceptual dysfunction seen in dementia with Lewy bodies.

Changes in Listing Plane Thickness Caused by Vestibular Schwannoma

Three-dimensional analysis of video-oculograms can be used to calculate Listing plane for patients and experimental subjects. Listing plane reflects the head's orientation with respect to gravity, which suggests that the plane is derived from otolithic vestibular input, itself, or from a gravity-oriented internal model constructed through integration of visual, vestibular, and proprioceptive sensory inputs. The goal of this study was to determine whether the Listing plane can serve as a parameter for evaluating static (peripheral or central) vestibular function. Prospective study. Tertiary referral center. Healthy subjects and patients with unilateral vestibular schwannoma without any previous treatment. Diagnostic. Video-oculograms were recorded from healthy subjects (aged 36.8 ± 6.3 yr) and from patients (aged 60.3 ± 7.5 yr) during voluntary gaze with the head in an upright or each-side-down orientation, and the thicknesses of the calculated Listing planes were then compared. Results revealed thickening of the Listing plane in patients only when the head was in an impaired-side-down orientation (1.250 ± 0.795 and 1.074 ± 0.759 degrees in the right- and left-side-down head orientations in healthy subjects versus 2.222 ± 1.237 degrees in the impaired-side-down orientation in patients), and this thickening correlated with caloric weakness. By contrast, neither the sensation of postural instability nor postural disturbance in force platform recordings contributed to the thickness of Listing plane. The thickness of the Listing plane could be a novel parameter for quantitatively evaluating static vestibular (otolithic) function, although central compensation might exist.

Head roll influences perceived hand position

Visual and proprioceptive sensory inputs are naturally coded in different reference frames, i.e., eye-centered and body-centered, respectively. To use these signals in conjunction for motor planning or perception ultimately requires converting them into a common frame of reference using estimates of the relative orientation of the eyes, head, and body. Here, we examine whether extraretinal signals-specifically head roll-alter multisensory perception through noisy reference frame transformations. To do so, we examine the accuracy of visual localization relative to proprioceptive hand position for different head roll orientations. Subjects were required to judge whether a visual target was located closer or further and left or right (4-alternative forced-choice task) from their unseen hand. This was done for three different head roll rotations (-30, 0, and 30 deg). We show that eccentric head roll increased the variability in the subjects' ability to discriminate target location relative to the fingertip. We conclude that sensory perception is sensitive to body-geometry-dependent noise affecting the coordinate matching transformations of sensory data.

Complex Visual Hallucinations, Presumably Due to Subarachnoid Hemorrhage, Treated Successfully With Risperidone

Back to table of contents Previous article Next article LettersFull AccessComplex Visual Hallucinations, Presumably Due to Subarachnoid Hemorrhage, Treated Successfully With RisperidoneDavid R. Spiegel, M.D., and Tim Petersen, M.D.David R. SpiegelSearch for more papers by this author, M.D., and Tim PetersenSearch for more papers by this author, M.D.Published Online:1 Jul 2011AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: Visual hallucinations have several known nonpsychiatric etiologies and may be treated accordingly. We present, with interest, a case of a 56-year-old woman who developed complex visual hallucinations (CVH) status post-cerebrovascular accident (CVA) in her right middle cerebral artery (MCA) distribution. The hallucinations appear to have been successfully treated with risperidone.Case ReportOur patient is a 56-year-old, right-handed woman who presented with a large right-MCA aneurysm and several small left-MCA aneurysms. Her right-MCA aneurysm was successfully surgically repaired; no operative intervention was required for the left aneurysms. In addition to transient sensory and motor deficits, her son noted that after the surgery she would report seeing a woman and a black cat. She had no previous visual dysfunction, although, interestingly, her insight into the CVH improved even before medication treatment. Our patient returned 3 weeks later with new hemorrhages in her right-MCA area, with ischemia. No new surgeries were performed, and her condition stabilized after 1 week with appropriate medical intervention. During this admission, her CVHs persisted, and the authors were consulted because of her “behavioral disturbances.” There was no apparent association between the hallucinations and sleep or time of day. There were no reports of complex partial or generalized seizures. Per her son's report, she had no previous history of psychiatric illness, visual hallucinations, or auditory hallucinations. She had no history of substance abuse. She did not have fluctuating awareness or alertness; she had a Richmond Agitation And Sedation Scale score of 0 and 26/30 on the Mini-Mental State Exam. Risperidone 1.5 mg/day was prescribed in an attempt to treat her CVHs, which resolved within 7 days of initiating treatment.DiscussionAlthough the etiologies for CVHs have been reviewed elsewhere,1 our patient's phenomenology merits a discussion of delineating between Charles-Bonnet syndrome secondary to cortical stroke. With respect to the latter, CVHs may develop secondary to activated occipital cortical regions adjacent to stroke-damaged areas with associated visual field deficits,2 whereas stroke is generally regarded as a condition in which decreased afferent input that yields CVHs of a particular quality (straight ahead, colored, people, insight), although it also occurs in patients with visual-field defects and normal central acuity.3 The theories proposed to explain the etiology of both conditions fall into two categories. The “deafferentation” theory proposes that the lack of visual sensory input into the cortex causes spontaneous neuronal discharge leading to abnormal visual perceptions not unlike the phantom-limb syndrome. The second, “perceptual release” theory, is based on the premise that a normal sensory input inhibits irrelevant impulses from the conscious perception of images. Where there is a reduction in sensory input, the threshold to suppress irrelevant images cannot be achieved, and previously subconscious perceptions are “released” into consciousness, resulting in CVHs.4Risperidone has potent serotonin type-2 receptor antagonism and has been suggested by some authors to have efficacy in treatment of CVH through the blockade of such receptors in the visual cortex.5EVMS Dept. Of Psychiatry Norfolk, VA e-mail: [email protected]edu1. Manford M , Andermann F : Complex visual hallucinations: clinical and neurobiological insights. Brain 1998; 121:1819–1840Crossref, Medline, Google Scholar2. De Haan EH , Nys GM , van Zandvoort MJ , et al.: The physiological basis of visual hallucinations after damage to the primary visual cortex. NeuroReport 2007; 18:1177–1180Crossref, Medline, Google Scholar3. Schadlu AP , Schadlu R , Shepherd JB: Charles Bonnet syndrome: a review. Curr Opin Ophthalmol 2009; 20:219–222Crossref, Medline, Google Scholar4. Ashwin PT , Tsaloumas MD : Complex visual hallucinations (Charles Bonnet syndrome) in the hemianopic visual field following occipital infarction. J Neurol Sci 2007; 263(1–2):184–186Crossref, Medline, Google Scholar5. Howard RJ : Risperidone for visual hallucinations in the elderly. Eur Neuropsychopharmacol 1996; 6:28Crossref, Google Scholar FiguresReferencesCited byDetailsCited ByComplex Visual Hallucinations Associated With Parietal InfarctLokesh Shahani, M.D.1 January 2013 | The Journal of Neuropsychiatry and Clinical Neurosciences, Vol. 25, No. 1 Volume 23Issue 3 Summer 2011Pages E44-E44 Metrics PDF download History Published online 1 July 2011 Published in print 1 July 2011

Rethinking visual scene perception.

A classic puzzle in understanding visual scene perception is how to reconcile the physiological constraints of vision with the phenomenology of seeing. Vision captures information via discrete eye fixations, interrupted by saccadic suppression, and limited by retinal inhomogeneity. Yet scenes are effortlessly perceived as coherent, continuous, and meaningful. Two conceptualizations of scene representation will be contrasted. The traditional visual-cognitive model casts visual scene representation as an imperfect reflection of the visual sensory input alone. By contrast, a new multisource model casts visual scene representation in terms of an egocentric spatial framework that is 'filled-in' by visual sensory input, but also by amodal perception, and by expectations and by constraints derived from rapid-scene classification and object-to-context associations. Together, these nonvisual sources serve to 'simulate' a likely surrounding scene that the visual input only partially reveals. Pros and cons of these alternative views will be discussed. WIREs Cogn Sci 2012, 3:117-127. doi: 10.1002/wcs.149 For further resources related to this article, please visit the WIREs website.

Visuo-haptic interactions in unilateral spatial neglect: the cross modal judd illusion.

Unilateral spatial neglect (USN) has been mainly investigated in the visual modality; only few studies compared spatial neglect across different sensory modalities, and explored their multisensory interactions, with controversial results. We investigated the integration between vision and haptics, through a bisection task of a cross modal illusion, the Judd variant of the Müller-Lyer illusion. We examined right-brain-damaged patients with (n = 7) and without (n = 7) left USN, and neurologically unimpaired participants (n = 14) in the bisection of Judd stimuli under visual, haptic, and visuo-haptic presentation. Neglect patients showed the characteristic rightward bias in the bisection of the baseline stimuli in the visual modality, but not in the haptic and visuo-haptic conditions. The illusory effects were preserved in each group and in each modality, indicating that the processing of the cross modal illusion is independent of the presence of deficits of spatial attention and representation. Spatial neglect can be modality-specific, but visual and tactile sensory inputs are properly integrated.

Organization of GABAergic inhibition in the motor output layer of the superior colliculus

The direction and amplitude of saccadic eye movements are determined by the location of the center of gravity of burst activity over a neuronal population on the spatial map of the intermediate gray layer (SGI) of the superior colliculus (SC). GABAergic interneurons might play critical roles in shaping the activation field on the topographical map but, to understand the mechanism, basic information on the organization of inhibitory circuits is essential. In the present study, we investigated the electrophysiological and morphological properties of GABAergic neurons in SGI by whole-cell patch-clamp recordings and intracellular staining using biocytin in GAD67-GFP knock-in mice (PND17-22), in which GABAergic neurons specifically express GFP fluorescence. The most common firing properties among these GABAergic neurons (n=231) were fast spiking (58%), followed by burst spiking (29%), late spiking (8%) and, the least common, regular spiking (2%) and rapid spike inactivation (3%). Morphological analysis of axonal trajectories of intracellularly-labeled GABAergic neurons revealed three major subclasses: (i) intralaminar interneurons, which were further divided into two subclasses, local and horizontal interneurons; (ii) interlaminar interneurons; and (iii) commissural and tectofugal neurons. These results reveal distinct subsets of GABAergic neurons including neurons that mediate local and long-range inhibition in the SC, neurons that potentially modulate visual and other sensory inputs to the SC, and neurons that project to nuclei outside the SC.

Amygdalar roles during exposure to a live predator and to a predator-associated context

The amygdala plays a critical role in determining the emotional significance of sensory stimuli and the production of fear-related responses. Large amygdalar lesions have been shown to practically abolish innate defensiveness to a predator; however, it is not clear how the different amygdalar systems participate in the defensive response to a live predator. Our first aim was to provide a comprehensive analysis of the amygdalar activation pattern during exposure to a live cat and to a predator-associated context. Accordingly, exposure to a live predator up-regulated Fos expression in the medial amygdalar nucleus (MEA) and in the lateral and posterior basomedial nuclei, the former responding to predator-related pheromonal information and the latter two nuclei likely to integrate a wider array of predatory sensory information, ranging from olfactory to non-olfactory ones, such as visual and auditory sensory inputs. Next, we tested how the amygdalar nuclei most responsive to predator exposure (i.e. the medial, posterior basomedial and lateral amygdalar nuclei) and the central amygdalar nucleus (CEA) influence both unconditioned and contextual conditioned anti-predatory defensive behavior. Medial amygdalar nucleus lesions practically abolished defensive responses during cat exposure, whereas lesions of the posterior basomedial or lateral amygdalar nuclei reduced freezing and increased risk assessment displays (i.e. crouch sniff and stretch postures), a pattern of responses compatible with decreased defensiveness to predator stimuli. Moreover, the present findings suggest a role for the posterior basomedial and lateral amygdalar nuclei in the conditioning responses to a predator-related context. We have further shown that the CEA does not seem to be involved in either unconditioned or contextual conditioned anti-predatory responses. Overall, the present results help to clarify the amygdalar systems involved in processing predator-related sensory stimuli and how they influence the expression of unconditioned and contextual conditioned anti-predatory responses.

Generalization patterns during reach adaptation to target jump

Event Abstract Back to Event Generalization patterns during reach adaptation to target jump Stephanie Westendorff1*, Bahareh Taghizadeh1 and Alexander Gail1 1 German Primate Center, Sensorimotor Group, BCCN Göttingen, Germany In typical visuomotor rotation tasks, adaptation is induced by a mismatch between visual and proprioceptive sensory input. Target-jump paradigms, i.e. tasks with sudden displacement of the movement target during movement initiation or execution, do not induce cross-modal mismatch, nor do they induce adaptation when subject are aware of the displacement. Here we present and characterize a novel target jump paradigm, in which reach movements reliably get adapted to target displacements. Subjects had to make center-out reaches to a peripheral target. Simultaneously they had to make a saccade to a neutral target. Saccadic suppression during the eye movement allowed us to displace the reach target during hand movement initiation or execution, without subjects noticing the perturbation. The reach target was displaced either to a different eccentricity (radial displacement) or to a different angular (directional displacement).Subjects incrementally adapted to the radial and to the directional displacement, with average learning rates similar to prism adaptation, and showed reliable negative aftereffects.We also tested the generalization of the adaptation effect to neighboring reach targets. Subjects were first adapted to either a radial or directional target displacement, and then probed at different positions along the radius and circumference of the adapted target. Preliminary analysis of our results suggests that movement endpoints to novel targets are off-set by a vector that is approximately equal to the displacement vector imposed on the adapted target. The offset decreases with increasing angular or radial distance from the adapted target.Our results show that reach adaptation in a target-jump experiment is possible when the displacement is obscured by a simultaneous saccade to a different target. The observed generalization patterns may be difficult to explain as a combination of independent adjustments on the direction and extent of movement. Consequently, our results may cast doubt on an earlier claim that direction and extent of movements are planned independently (Krakauer, Pine, Ghilardi, and Ghez, J Neurosci, 2000). Figure 1: Reach endpoint adaptation to 15º directional target jump. Reach errors are shown as angular deviation over trials for 6 subjects. Figure 1 Keywords: computational neuroscience Conference: Bernstein Conference on Computational Neuroscience, Berlin, Germany, 27 Sep - 1 Oct, 2010. Presentation Type: Presentation Topic: Bernstein Conference on Computational Neuroscience Citation: Westendorff S, Taghizadeh B and Gail A (2010). Generalization patterns during reach adaptation to target jump. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference on Computational Neuroscience. doi: 10.3389/conf.fncom.2010.51.00018 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: 22 Sep 2010; Published Online: 23 Sep 2010. * Correspondence: Dr. Stephanie Westendorff, German Primate Center, Sensorimotor Group, BCCN Göttingen, Göttingen, Germany, swesten@gwdg.de 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 Stephanie Westendorff Bahareh Taghizadeh Alexander Gail Google Stephanie Westendorff Bahareh Taghizadeh Alexander Gail Google Scholar Stephanie Westendorff Bahareh Taghizadeh Alexander Gail PubMed Stephanie Westendorff Bahareh Taghizadeh Alexander Gail 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.

Enhanced effectiveness in visuo‐haptic object‐selective brain regions with increasing stimulus salience

The occipital and parietal lobes contain regions that are recruited for both visual and haptic object processing. The purpose of the present study was to characterize the underlying neural mechanisms for bimodal integration of vision and haptics in these visuo-haptic object-selective brain regions to find out whether these brain regions are sites of neuronal or areal convergence. Our sensory conditions consisted of visual-only (V), haptic-only (H), and visuo-haptic (VH), which allowed us to evaluate integration using the superadditivity metric. We also presented each stimulus condition at two different levels of signal-to-noise ratio or salience. The salience manipulation allowed us to assess integration using the rule of inverse effectiveness. We were able to localize previously described visuo-haptic object-selective regions in the lateral occipital cortex (lateral occipital tactile-visual area) and the intraparietal sulcus, and also localized a new region in the left anterior fusiform gyrus. There was no evidence of superadditivity with the VH stimulus at either level of salience in any of the regions. There was, however, a strong effect of salience on multisensory enhancement: the response to the VH stimulus was more enhanced at higher salience across all regions. In other words, the regions showed enhanced integration of the VH stimulus with increasing effectiveness of the unisensory stimuli. We called the effect "enhanced effectiveness." The presence of enhanced effectiveness in visuo-haptic object-selective brain regions demonstrates neuronal convergence of visual and haptic sensory inputs for the purpose of processing object shape.

The Effects of Overfeeding on the Neuronal Response to Visual Food Cues in Thin and Reduced-Obese Individuals

BackgroundThe regulation of energy intake is a complex process involving the integration of homeostatic signals and both internal and external sensory inputs. The objective of this study was to examine the effects of short-term overfeeding on the neuronal response to food-related visual stimuli in individuals prone and resistant to weight gain.Methodology/Principal Findings22 thin and 19 reduced-obese (RO) individuals were studied. Functional magnetic resonance imaging (fMRI) was performed in the fasted state after two days of eucaloric energy intake and after two days of 30% overfeeding in a counterbalanced design. fMRI was performed while subjects viewed images of foods of high hedonic value and neutral non-food objects. In the eucaloric state, food as compared to non-food images elicited significantly greater activation of insula and inferior visual cortex in thin as compared to RO individuals. Two days of overfeeding led to significant attenuation of not only insula and visual cortex responses but also of hypothalamus response in thin as compared to RO individuals.Conclusions/SignificanceThese findings emphasize the important role of food-related visual cues in ingestive behavior and suggest that there are important phenotypic differences in the interactions between external visual sensory inputs, energy balance status, and brain regions involved in the regulation of energy intake. Furthermore, alterations in the neuronal response to food cues may relate to the propensity to gain weight.

The effects of overfeeding and propensity to weight gain on the neuronal responses to visual food cues

Obesity is a serious and growing public health problem in the United States and the world. The pathophysiological processes that underlie the increasing prevalence of obesity have not been clearly defined but likely involve faulty interactions between environmental factors, which favor positive energy balance, and weight regulatory systems in genetically susceptible individuals. Individuals who are genetically predisposed to thinness in the current environment may be able to sense and respond to excess energy intake more rapidly and accurately than those predisposed to obesity. The regulation of energy intake and therefore the potential adaptation to changes in energy balance is a complex process with interactions between homeostatic and non-homeostatic signals likely being critical. We have observed that thin (obese-resistant) individuals quickly sense changes in positive energy balance with not only changes in measures of appetite but also in brain regions important for the regulation of energy intake. This is in contrast to reduced-obese (obese-prone) individuals who do not appear to appropriately sense the changes in positive energy balance, suggesting that there is a differential sensitivity to positive energy balance between obese-resistant and obese-prone individuals. We have also found evidence for important interactions between external food cues and activation of brain regions important in the homeostatic regulation of energy balance. These findings emphasize the important role of environmental visual cues and suggest that there are important phenotypic differences in the interactions between external visual sensory inputs, energy balance status, and brain regions important in the regulation of energy intake.

Visual and tactile integration in action comprehension and execution

Humans rely on the integration of information from multiple sensory modalities to interact successfully with their environment. In the present series of studies, we investigated how the visuomotor system integrates congruent and incongruent visual and tactile sensory inputs for goal-directed action comprehension and execution. Specifically, we investigated whether orienting of attention towards vision, touch, or both vision and touch enhances the impact of one modality over another. In Experiment 1 participants were presented with visual (on a computer monitor) and/or tactile (in unseen left hand) sensory inputs of an action, and made button-press responses to categorise it as ‘wide’ or ‘narrow’. Responses were significantly faster when attending to vision compared with touch, and faster in fully congruent compared with grasp congruent and incongruent conditions. Thus, both vision and touch are significant in action comprehension, but visual inputs are in general more influential than tactile inputs. Moreover, responses to wide grasp actions were significantly faster than to narrow-grasp actions. In Experiment 2 the same task was performed but the participants made reach-to-grasp movements, recorded with ProReflex motion capture system. Although actions to wide objects produced wider peak grasp overall than to a narrow object, in contrast to action comprehension, there was no systematic effect of attended modality or tactile input in action execution. We speculate that action comprehension and execution utilize visual and tactile inputs differentially.