Activity In Primary Visual Cortex Research Articles

Head Movements Control the Activity of Primary Visual Cortex in a Luminance-Dependent Manner

The vestibular system broadcasts head-movement-related signals to sensory areas throughout the brain, including visual cortex. These signals are crucial for the brain's ability to assess whether motion of the visual scene results from the animal's head movements. However, how head movements affect visual cortical circuits remains poorly understood. Here, we discover that ambient luminance profoundly transforms how mouse primary visual cortex (V1) processes head movements. While in darkness, head movements result in overall suppression of neuronal activity; in ambient light, the same head movements trigger excitation across all cortical layers. This light-dependent switch in how V1 processes head movements is controlled by somatostatin-expressing (SOM) inhibitory neurons, which are excited by head movements in dark, but not in light. This study thus reveals a light-dependent switch in the response of V1 to head movements and identifies a circuit in which SOM cells are key integrators of vestibular and luminance signals.

Encoding of 3D Head Orienting Movements in the Primary Visual Cortex

Animals actively sample the sensory world by generating complex patterns of movement that evolve in three dimensions. Whether or how such movements affect neuronal activity in sensory cortical areas remains largely unknown, because most experiments exploring movement-related modulation have been performed in head-fixed animals. Here, we show that 3D head-orienting movements (HOMs) modulate primary visual cortex (V1) activity in a direction-specific manner that also depends on light. We identify two overlapping populations of movement-direction-tuned neurons that support this modulation, one of which is direction tuned in the dark and the other in the light. Although overall movement enhanced V1 responses to visual stimulation, HOMs suppressed responses. We demonstrate that V1 receives a motor efference copy related to orientation from secondary motor cortex, which is involved in controlling HOMs. These results support predictive coding theories of brain function and reveal a pervasive role of 3D movement in shaping sensory cortical dynamics.

Eye-selective fMRI activity in human primary visual cortex: Comparison between 3 ​T and 9.4 ​T, and effects across cortical depth

The primary visual cortex of humans contains patches of neurons responding preferentially to stimulation of one eye (the ocular dominance columns). Multiple previous studies attempted to detect their activity using fMRI. The majority of these fMRI studies used magnetic field strengths of 4 ​T and higher. However, there have been reports of reliable eye-selective activations at 3 ​T as well. In this study we investigated the possibility of detecting eye-selective V1 activity using high-resolution GE-EPI fMRI at 3 ​T and sub-millimeter resolution fMRI at ultrahigh 9.4 ​T magnetic field strengths with acquisition parameters optimized for each field strength. High-resolution fMRI at 9.4 ​T also allowed us to examine the eye-selectivity responses across the cortical depth, which are expected to be strongest in the middle layers.We observed a substantial increase in the percentage of eye-selective voxels, as well as a doubling in run-to-run consistency of eye preference at ultrahigh field compared to 3 ​T. We also found that across cortical depth, eye selectivity increased towards the superficial layers, and that signal contrast increased while noise remained nearly constant towards the surface. The depth-resolved results are consistent with a distortion of spatial specificity of the GE-EPI signal by ascending venules and large draining veins on the cortical surface. The effects of larger vessels cause increasing signal amplitude, but also displacement of the maximum BOLD signal relative to neural activity.In summary, our results show that increase in spatial resolution, reduced partial volume effects, and improved sensitivity at 9.4 ​T allow for better detection of eye-selective signals related to ocular dominance columns. However, although ultrahigh field yields higher sensitivity to the ocular dominance signal, GE-EPI still suffers from specificity issues, with a prominent signal contribution at shallow depths from larger cortical vessels.

Biofeedback Rehabilitation and Visual Cortex Response in Stargardt's Disease: A Randomized Controlled Trial.

Purposeto evaluate the effect of biofeedback (BF) rehabilitation on the visual function and on the activity of primary visual cortex (PVC) in patients with Stargardt's disease owing to mutations in the ABCA4 gene (STGD1).MethodsThis was a single-center, controlled, randomized study. Twenty-four patients with STGD1 were randomized into two groups: a treatment group (TG) undergoing BF rehabilitation and a control group (CG). Treatment with BF consisted of a 10-minute session per eye performed weekly for 12 weeks. The subjects underwent a baseline and 3-month follow-up visits, including best-corrected visual acuity (BCVA), reading test, microperimetry, and functional magnetic resonance imaging (fMRI). The fMRI studies were acquired sequentially using a passive viewing condition and an active reading task. The primary outcomes were the change in the fMRI activation of primary visual cortex and the change in reading ability.ResultsAfter treatment, the patients in the TG were able to read smaller characters (P = 0.002) with a greater reading speed (P = 0.014) compared with patients in the CG. The fMRI studies showed a significant effect (P < 0.001) of BF on primary visual cortex activation in the TG compared with the CG. Finally, we observed significant (P < 0.05) improvements of best-corrected visual acuity, macular sensitivity, and fixation stability parameters in the TG compared with the CG.ConclusionsOur study showed that visual rehabilitation using BF improved the usage of residual visual function in patients with STGD1.Translational RelevanceOur findings show that the BF treatment compared with no treatment at all resulted in benefits. The specificity of the treatment could be examined to determine whether BF can be included in clinical practice.

Neural Correlates of Multisensory Detection Behavior: Comparison of Primary and Higher-Order Visual Cortex

We act upon stimuli in our surrounding environment by gathering the multisensory information they convey and by integrating this information to decide on a behavioral action. We hypothesized that the anterolateral secondary visual cortex (area AL) of the mouse brain may serve as a hub for sensorimotor transformation of audiovisual information. We imaged neuronal activity in primary visual cortex (V1) and AL of the mouse during a detection task using visual, auditory, and audiovisual stimuli. We found that AL neurons were more sensitive to weak uni- and multisensory stimuli compared to V1. Depending on contrast, different subsets of AL and V1 neurons showed cross-modal modulation of visual responses. During audiovisual stimulation, AL neurons showed stronger differentiation of behaviorally reported versus unreported stimuli compared to V1, whereas V1 showed this distinction during unisensory visual stimulation. Thus, neural population activity in area AL correlates more closely with multisensory detection behavior than V1.

Spatial attention enhances network, cellular and subthreshold responses in mouse visual cortex

Internal brain states strongly modulate sensory processing during behaviour. Studies of visual processing in primates show that attention to space selectively improves behavioural and neural responses to stimuli at the attended locations. Here we develop a visual spatial task for mice that elicits behavioural improvements consistent with the effects of spatial attention, and simultaneously measure network, cellular, and subthreshold activity in primary visual cortex. During trial-by-trial behavioural improvements, local field potential (LFP) responses to stimuli detected inside the receptive field (RF) strengthen. Moreover, detection inside the RF selectively enhances excitatory and inhibitory neuron responses to task-irrelevant stimuli and suppresses noise correlations and low frequency LFP fluctuations. Whole-cell patch-clamp recordings reveal that detection inside the RF increases synaptic activity that depolarizes membrane potential responses at the behaviorally relevant location. Our study establishes that mice display fundamental signatures of visual spatial attention spanning behavioral, network, cellular, and synaptic levels, providing new insight into rapid cognitive enhancement of sensory signals in visual cortex.

Paroxetine can improve primary visual cortex activity in a high-risk mouse model of schizophrenia

Visual cortex functional deficits can be observed in schizophrenia patients and in individuals at high risk of schizophrenia. However, to date, few studies have investigated methods to improve these functional deficits. This study aimed to investigate the pathological change in the primary visual cortex of a prenatal MK-801-induced high-risk mouse model of schizophrenia (HRMMS) and to test the effect of paroxetine on visual cortex activity. Pregnant mice were given a systemic injection of MK-801, and male offspring that did not present schizophrenia-like behaviors in early adulthood were defined as HRMMS. Some of the HRMMS mice were treated with pharmacological agents beginning at 4 weeks of age. After 4 weeks of treatment with risperidone and/or paroxetine, two-photon calcium imaging was performed to analyze the primary visual cortex activity. The sucrose preference test and the prepulse inhibition (PPI) apparatus test were used to assess the cognitive and behavioral performance. HRMMS mice with or without risperidone treatment had impairments in the primary visual cortex as observed by reduced neuronal calcium activity. Risperidone plus paroxetine and paroxetine alone treatments increased the neuronal calcium activity in the primary visual cortex. Notably, the neuronal calcium activity was higher in mice treated with paroxetine alone. Treatment with paroxetine alone also improved the cognitive and behavioral performance better than treatment with risperidone plus paroxetine. Our pioneering animal model showed that treatment with paroxetine alone improves visual cortex impairments in HRMMS mice better than treatment with risperidone plus paroxetine, indicating that antipsychotics cannot normalize visual cortex impairments.

Functional MRI study in a case of Charles Bonnet syndrome related to LHON

IntroductionCharles Bonnet syndrome is characterized by simple or complex visual hallucinations (VH) due to damage along the visual pathways. We report a functional MRI study of brain correlates of VH in the context of a severe optic atrophy in a patient with Leber’s Hereditary Optic Neuropathy (LHON).Case reportA 62-year-old man was diagnosed with LHON (11778/ND4 mtDNA mutation) after subacute visual loss in left eye (right eye was amblyopic). One month later, he experienced VH of a few seconds consisting in “moving red and blue miniature cartoons”. One year later VH content changed in colored mosaic (10–15 s duration), usually stress-related, and blue and white flashes (2–5 s), triggered by unexpected auditory stimuli. Audiometry revealed mild sensorineural hearing loss. Three block design functional MRI paradigms were administrated: 1) random “clap”, 2) “checkerboard” and 3) non-random “beep”. After random “claps” simple flashes were evoked with bilateral activation of primary and secondary visual cortex, cuneus, precuneus and insula. Neither hallucinations nor cortex activation were registered after “checkerboard” stimulation, due to the severe visual impairment. Primary and secondary auditory cortices were “beep”-activated, without eliciting VH by non-random “beep”.ConclusionsThe peculiarity of our case is that VH were triggered by random auditory stimuli, possibly due to a cross-modal plasticity between visual and auditory networks, likely influenced by the sensorineural deafness. Functional alterations of both networks in resting conditions have been demonstrated in LHON patients, even without an auditory deficit. Finally, the absence of VH triggered by expected stimuli is consistent with the “expectation suppression theory”, based on increased neural activations after unexpected but not by predicted events.

Manipulating visual scanpaths during facial emotion perception modulates functional brain activation in schizophrenia patients and controls.

Individuals with schizophrenia exhibit deficits in facial emotion processing, which have been associated with abnormalities in visual gaze behavior and functional brain activation. However, the relationship between gaze behavior and brain activation in schizophrenia remains unexamined. Studies in healthy individuals and other clinical samples indicate a relationship between gaze behavior and functional activation in brain regions implicated in facial emotion processing deficits in schizophrenia (e.g., fusiform gyrus), prompting the question of whether a similar relationship exists in schizophrenia. This study examined whether manipulating visual scanpaths during facial emotion perception would modulate functional brain activation in a sample of 23 schizophrenia patients and 26 community controls. Participants underwent functional magnetic resonance imaging (MRI) while viewing pictures of emotional faces. During the typical viewing condition, a fixation cue directed participants' gaze primarily to the eyes and mouth, whereas during the atypical viewing condition gaze was directed to peripheral features. Both viewing conditions elicited a robust response throughout face-processing regions. Typical viewing led to greater activation in visual association cortex including the right inferior occipital gyrus/occipital face area, whereas atypical viewing elicited greater activation in primary visual cortex and regions involved in attentional control. There were no between-groups activation differences in response to faces or interaction between group and gaze manipulation. The results indicate that gaze behavior modulates functional activation in early face-processing regions in individuals with and without schizophrenia, suggesting that abnormal gaze behavior in schizophrenia may contribute to activation abnormalities during facial emotion perception. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Altered effective connectivity of primary visual cortex in primary angle closure glaucoma using Granger causality analysis

Background Previous neuroimaging studies demonstrated that primary angle closure glaucoma patients were associated with abnormal intrinsic brain activity in primary visual cortex (V1). Purpose The purpose of this study was to investigate the effective connectivity patterns of V1 in patients with primary angle closure glaucoma. Material and Methods Thirty-seven patients with primary angle closure glaucoma (20 men, 17 women) and 36 healthy controls (20 men, 16 women) closely matched for age, sex, and education, underwent resting-state MRI scans. A voxel-wise Granger causality analysis method was performed to explore different effective connectivity pattern of V1 between the two groups. Results Compared with healthy controls, patients with primary angle closure glaucoma showed decreased effective connectivity from the left V1 to left cuneus and increased effective connectivity from the left V1 to left precentral gyrus and right supplementary motor area. Meanwhile, patients with primary angle closure glaucoma showed decreased effective connectivity from left precentral gyrus to left V1 and right frontal middle gyrus to left V1. In addition, patients with primary angle closure glaucoma showed a decreased effective connectivity from the right V1 to left cuneus/calcarine and increased effective connectivity from the right V1 to left inferior frontal gyrus and right caudate. Meanwhile, patients with primary angle closure glaucoma showed decreased effective connectivity from right middle frontal gyrus/precentral gyrus to right V1 and left precentral gyrus to right V1. Conclusion Our results highlighted that patients with primary angle closure glaucoma had abnormal effective connectivity between V1 and higher visual area, motor cortices, somatosensory cortices, and frontal lobe, which indicated that they might present with abnormal top-down modulations, visual imagery, vision-motor function, and vision-related higher cognition function.

The functional neuroanatomy of emotion processing in frontotemporal dementias.

Impaired processing of emotional signals is a core feature of frontotemporal dementia syndromes, but the underlying neural mechanisms have proved challenging to characterize and measure. Progress in this field may depend on detecting functional changes in the working brain, and disentangling components of emotion processing that include sensory decoding, emotion categorization and emotional contagion. We addressed this using functional MRI of naturalistic, dynamic facial emotion processing with concurrent indices of autonomic arousal, in a cohort of patients representing all major frontotemporal dementia syndromes relative to healthy age-matched individuals. Seventeen patients with behavioural variant frontotemporal dementia [four female; mean (standard deviation) age 64.8 (6.8) years], 12 with semantic variant primary progressive aphasia [four female; 66.9 (7.0) years], nine with non-fluent variant primary progressive aphasia [five female; 67.4 (8.1) years] and 22 healthy controls [12 female; 68.6 (6.8) years] passively viewed videos of universal facial expressions during functional MRI acquisition, with simultaneous heart rate and pupillometric recordings; emotion identification accuracy was assessed in a post-scan behavioural task. Relative to healthy controls, patient groups showed significant impairments (analysis of variance models, all P < 0.05) of facial emotion identification (all syndromes) and cardiac (all syndromes) and pupillary (non-fluent variant only) reactivity. Group-level functional neuroanatomical changes were assessed using statistical parametric mapping, thresholded at P < 0.05 after correction for multiple comparisons over the whole brain or within pre-specified regions of interest. In response to viewing facial expressions, all participant groups showed comparable activation of primary visual cortex while patient groups showed differential hypo-activation of fusiform and posterior temporo-occipital junctional cortices. Bi-hemispheric, syndrome-specific activations predicting facial emotion identification performance were identified (behavioural variant, anterior insula and caudate; semantic variant, anterior temporal cortex; non-fluent variant, frontal operculum). The semantic and non-fluent variant groups additionally showed complex profiles of central parasympathetic and sympathetic autonomic involvement that overlapped signatures of emotional visual and categorization processing and extended (in the non-fluent group) to brainstem effector pathways. These findings open a window on the functional cerebral mechanisms underpinning complex socio-emotional phenotypes of frontotemporal dementia, with implications for novel physiological biomarker development.

Fitting predictive coding to the neurophysiological data

Recent neurophysiological data showing the effects of locomotion on neural activity in mouse primary visual cortex has been interpreted as providing strong support for the predictive coding account of cortical function. Specifically, this work has been interpreted as providing direct evidence that prediction-error, a distinguishing property of predictive coding, is encoded in cortex. This article evaluates these claims and highlights some of the discrepancies between the proposed predictive coding model and the neuro-biology. Furthermore, it is shown that the model can be modified so as to fit the empirical data more successfully.

Neural Correlates of Enhanced Audiovisual Processing in the Bilingual Brain

Bilingualism is associated with enhancements in perceptual and cognitive processing necessary for juggling multiple languages. Recent psychophysical studies demonstrate bilinguals also show enhanced multisensory processing and more restricted temporal binding windows for integrating audiovisual information. Here, we probed the neural mechanisms of bilinguals’ audiovisual benefits. We recorded neuroelectric responses in mono- and bi-lingual listeners to the double-flash paradigm in which auditory beeps concurrent with a single visual flash induces the perceptual illusion of multiple flashes. Relative to monolinguals, bilinguals showed less susceptibility to the illusion (fewer false perceptual reports) coupled with stronger and faster event-related potentials to audiovisual information. Source analyses of EEG data revealed monolinguals’ increased propensity for erroneously perceiving audiovisual stimuli was attributed to increased activity in primary visual (V1) and auditory cortex (PAC), increases in multisensory association areas (BA 37), but reduced frontal activity (BA 10). Regional activations were associated with an opposite pattern of behaviors: whereas stronger V1 and PAC activity predicted slower behavioral responses, stronger frontal BA10 responses elicited faster judgments. Our results suggest bilinguals’ higher precision in audiovisual perception reflects more veridical sensory coding of physical cues coupled with superior top-down gating of sensory information to suppress the generation of false percepts. Findings underscore that the plasticity afforded by speaking multiple languages shapes extra-linguistic brain regions and can enhance audiovisual brain processing in a domain-general manner.

SU66 - THE DCDC2/INTRON 2 DELETION AND MAGNOCELLULAR VISUAL STREAM: A PRELIMINARY FMRI STUDY IN DEVELOPMENTAL DYSLEXIA TESTING MAIN EFFECTS AND INTERACTIONS

Background DCDC2 is a leading susceptibility gene in Developmental Dyslexia (DD) and reading ability. A DCDC2/intron 2 deletion (DCDC2d), encompassing the Regulatory Element Associated with Dyslexia 1 (READ1) region, has been linked to DD and structural and functional brain areas underlying reading acquisition in subjects with DD and in normal readers (NR) (for a review, Mascheretti et al., 2017). DCDC2d influences motion perception, a psychophysical characteristic tapping the magnocellular (M) stream, in reading (dis)ability (Cicchini et al., 2015; Gori et al., 2015). The M stream provides early accurate visual analysis of stimuli prior to grapheme-phoneme integration (Vidyasagar, 1999). Data reveal its impairment in DD (Stein, 2014). To investigate DCDC2d effects on M stream functionality, we implemented an fMRI study on children with DD and NR, grouped according to the presence(+)/absence(-) of DCDC2d, to assess contrast sensitivity at different temporal and spatial frequencies tapping the M and parvocellular (P) streams. Methods We studied 53 children: 11 DD+ (mean age:14.1±1.9; F/M:1/10), 16 DD- (mean age:13.9±1.7; F/M:5/11), 8 NR+ (mean age:12.9±1.6; F/M:4/4), 18 NR- (mean age:12.1±1.9; F/M:7/11), with a block-design fMRI visual task on a 3 T scanner (TR=2 s, voxel 3×3×3.5mm3; time 12’04”). The stimuli consisted of two full-field sinusoidal gratings shown for 14 s at different orientations with sinusoidal counterphase flicker to activate either the M or P streams (Denison et al., 2014). Subjects performed a target detection task during 16 M and 8 P pseudorandom blocks, to encourage them to constantly follow the visual stimuli. A 2-way ANOVA in SPM12 (Friston et al., 2007) tested the main effects and interactions of DD and DCDC2d. The significance threshold was p The local Bioethics Committee approved the study and parents gave written informed consent. Results During the M stimuli, subjects with DCDC2d, regardless of DD, showed reduced activation in the left V1, and higher activations in the right precuneus, the left fusiform and temporal gyri, and insula. Moreover, children with DD, regardless of DCDC2d, showed reduced activations in the left V1, lingual gyrus and right fusiform gyrus, and higher activation in the left middle and superior temporal gyrus. No significant interactions were found at the significance threshold. Discussion During a visual task stimulating the M streams, irrespective of DD, DCDC2d accounted for activations in primary visual cortex and reading-related brain areas in the ventral stream involved in word recognition, phonological processing and grapheme-phoneme correspondence (fusiform and temporal gyri), and in speech and language processing (insula). Findings suggest that new hypothesis-driven imaging–genetic studies would lead to the identification of neurofunctional variations belonging to the DD ‘functional phenotype’. As previously described, children with DD showed different activations in visual (V1) and reading-related brain areas (lingual, fusiform and temporal gyri), supporting the idea that altered cortico-cortical connectivity of the language and visual areas might represent a mechanism underlying DD. Finally, significant interactions between DD and DCDC2d may plausibly exist; larger sample sizes are needed to support this hypothesis and to confirm this preliminary data.

Linking V1 Activity to Behavior.

A long-term goal of visual neuroscience is to develop and test quantitative models that account for the moment-by-moment relationship between neural responses in early visual cortex and human performance in natural visual tasks. This review focuses on efforts to address this goal by measuring and perturbing the activity of primary visual cortex (V1) neurons while nonhuman primates perform demanding, well-controlled visual tasks. We start by describing a conceptual approach-the decoder linking model (DLM) framework-in which candidate decoding models take neural responses as input and generate predicted behavior as output. The ultimate goal in this framework is to find the actual decoder-the model that best predicts behavior from neural responses. We discuss key relevant properties of primate V1 and review current literature from the DLM perspective. We conclude by discussing major technological and theoretical advances that are likely to accelerate our understanding of the link between V1 activity and behavior.

In Vivo Imaging of Cellular Excitation-Transcription Coupling in the Mouse Brain

Regulation of gene transcription is essential for long-term plasticity in the brain. However, it has not been possible to monitor dynamics of neuronal transcription in vivo and to correlate them to neuronal activity patterns at cellular resolution. Here we present a technique to image in vivo signaling of cAMP response element binding protein (CREB), an activity-dependent transcription factor important for synaptic plasticity, using 2-photon fluorescence lifetime imaging (2pFLIM) in combination with new FRET biosensors. This allowed for long-term simultaneous imaging of CREB and neuronal activity in cortical neurons of awake animals. We found that, on average, CREB activity is positively correlated with behavioral performance in a motor learning task. Further, we performed chronic dual-imaging of CREB and neuronal activity in primary visual cortex, identifying a correlation between CREB and neuronal activity dynamics following sensory deprivation. This approach will allow researchers to unravel transcriptional dynamics underlying experience-dependent plasticity in the brain.

Hierarchical stimulus processing in rodent primary and lateral visual cortex as assessed through neuronal selectivity and repetition suppression

Similar to primates, visual cortex in rodents appears to be organized in two distinct hierarchical streams. However, there is still little known about how visual information is processed along those streams in rodents. In this study, we examined how repetition suppression and position and clutter tolerance of the neuronal representations evolve along the putative ventral visual stream in rats. To address this question, we recorded multiunit spiking activity in primary visual cortex (V1) and the more downstream visual laterointermediate (LI) area of head-restrained Long-Evans rats. We employed a paradigm reminiscent of the continuous carry-over design used in human neuroimaging. In both areas, stimulus repetition attenuated the early phase of the neuronal response to the repeated stimulus, with this response suppression being greater in area LI. Furthermore, stimulus preferences were more similar across positions (position tolerance) in area LI than in V1, even though the absolute responses in both areas were very sensitive to changes in position. In contrast, the neuronal representations in both areas were equally good at tolerating the presence of limited visual clutter, as modeled by the presentation of a single flank stimulus. When probing tolerance of the neuronal representations with stimulus-specific adaptation, we detected no position tolerance in either examined brain area, whereas, on the contrary, we revealed clutter tolerance in both areas. Overall, our data demonstrate similarities and discrepancies in processing of visual information along the ventral visual stream of rodents and primates. Moreover, our results stress caution in using neuronal adaptation to probe tolerance of the neuronal representations. NEW & NOTEWORTHY Rodents are emerging as a popular animal model that complement primates for studying higher level visual functions. Similar to findings in primates, we demonstrate a greater repetition suppression and position tolerance of the neuronal representations in the downstream laterointermediate area of Long-Evans rats compared with primary visual cortex. However, we report no difference in the degree of clutter tolerance between the areas. These findings provide additional evidence for hierarchical processing of visual stimuli in rodents.

Volitional Modulation of Primary Visual Cortex Activity Requires the Basal Ganglia

Animals acquire behaviors through instrumental conditioning. Brain-machine interfaces have used instrumental conditioning to reinforce patterns of neural activity directly, especially in frontal and motor cortices, which are a rich source of signals for voluntary action. However, evidence suggests that activity in primary sensory cortices may also reflect internally driven processes, instead of purely encoding antecedent stimuli. Here, we show that rats and mice can learn to produce arbitrary patterns of neural activity in their primary visual cortex to control an auditory cursor and obtain reward. Furthermore, learning was prevented when neurons in the dorsomedial striatum (DMS), which receives input from visual cortex, were optogenetically inhibited, but not during inhibition of nearby neurons in the dorsolateral striatum. After learning, DMS inhibition did not affect production of the rewarded patterns. These data demonstrate that cortico-basal ganglia circuits play a general role in learning to produce cortical activity that leads to desirable outcomes.

Entropy factor for randomness quantification in neuronal data

A novel measure of neural spike train randomness, an entropy factor, is proposed. It is based on the Shannon entropy of the number of spikes in a time window and can be seen as an analogy to the Fano factor. Theoretical properties of the new measure are studied for equilibrium renewal processes and further illustrated on gamma and inverse Gaussian probability distributions of interspike intervals. Finally, the entropy factor is evaluated from the experimental records of spontaneous activity in macaque primary visual cortex and compared to its theoretical behavior deduced for the renewal process models. Both theoretical and experimental results show substantial differences between the Fano and entropy factors. Rather paradoxically, an increase in the variability of spike count is often accompanied by an increase of its predictability, as evidenced by the entropy factor.

Visually Driven Neuropil Activity and Information Encoding in Mouse Primary Visual Cortex.

Cortical neuropil modulations recorded by calcium imaging reflect the activity of large aggregates of axo-dendritic processes and synaptic compartments from a large number of neurons. The organization of this activity impacts neuronal firing but is not well understood. Here we used in vivo 2-photon imaging with Oregon Green Bapta (OGB) and GCaMP6s to study neuropil visual responses to moving gratings in layer 2/3 of mouse area V1. We found neuropil responses to be strongly modulated and more reliable than neighboring somatic activity. Furthermore, stimulus independent modulations in neuropil activity, i.e., noise correlations, were highly coherent across the cortical surface, up to distances of at least 200 μm. Pairwise neuropil-to-neuropil-patch noise correlation strength was much higher than cell-to-cell noise correlation strength and depended strongly on brain state, decreasing in quiet wakefulness relative to light anesthesia. The profile of neuropil noise correlation strength decreased gently with distance, dropping by ~11% at a distance of 200 μm. This was comparatively slower than the profile of cell-to-cell noise correlations, which dropped by ~23% at 200 μm. Interestingly, in spite of the “salt & pepper” organization of orientation and direction encoding across mouse V1 neurons, populations of neuropil patches, even of moderately large size (radius ~100 μm), showed high accuracy for discriminating perpendicularly moving gratings. This was commensurate to the accuracy of corresponding cell populations. The dynamic, stimulus dependent, nature of neuropil activity further underscores the need to carefully separate neuropil from cell soma activity in contemporary imaging studies.