Visual Cortex Excitability Research Articles

Always expect the unexpected: eye position modulates visual cortex excitability in a stimulus-free environment.

Stimuli that potentially require a rapid defensive or avoidance action can appear from the periphery at any time in natural environments. de Wit et al. (Cortex 127: 120-130, 2020) recently reported novel evidence suggestive of a fundamental neural mechanism that allows organisms to effectively deal with such situations. In the absence of any task, motor cortex excitability was found to be greater whenever gaze was directed away from either hand. If modulation of cortical excitability as a function of gaze location is a fundamental principle of brain organization, then one would expect its operation to be present outside of motor cortex, including brain regions involved in perception. To test this hypothesis, we applied single-pulse transcranial magnetic stimulation (TMS) to the right lateral occipital lobe while participants directed their eyes to the left, straight-ahead, or to the right, and reported the presence or absence of a phosphene. No external stimuli were presented. Cortical excitability as reflected by the proportion of trials on which phosphenes were elicited from stimulation of the right visual cortex was greater with eyes deviated to the right as compared with the left. In conjunction with our previous findings of change in motor cortex excitability when gaze and effector are not aligned, this eye position-driven change in visual cortex excitability presumably serves to facilitate the detection of stimuli and subsequent readiness to act in nonfoveated regions of space. The existence of this brain-wide mechanism has clear adaptive value given the unpredictable nature of natural environments in which human beings are situated and have evolved.NEW & NOTEWORTHY For many complex tasks, humans focus attention on the site relevant to the task at hand. Humans evolved and live in dangerous environments, however, in which threats arise from outside the attended site; this fact necessitates a process by which the periphery is monitored. Using single-pulse transcranial magnetic stimulation (TMS), we demonstrated for the first time that eye position modulates visual cortex excitability. We argue that this underlies at least in part what we term "surveillance attention."

Visual hallucinations induced by Ganzflicker and Ganzfeld differ in frequency, complexity, and content

Visual hallucinations can be phenomenologically divided into those of a simple or complex nature. Both simple and complex hallucinations can occur in pathological and non-pathological states, and can also be induced experimentally by visual stimulation or deprivation—for example using a high-frequency, eyes-open flicker (Ganzflicker) and perceptual deprivation (Ganzfeld). Here we leverage the differences in visual stimulation that these two techniques involve to investigate the role of bottom-up and top-down processes in shifting the complexity of visual hallucinations, and to assess whether these techniques involve a shared underlying hallucinatory mechanism despite their differences. For each technique, we measured the frequency and complexity of the hallucinations produced, utilising button presses, retrospective drawing, interviews, and questionnaires. For both experimental techniques, simple hallucinations were more common than complex hallucinations. Crucially, we found that Ganzflicker was more effective than Ganzfeld at eliciting simple hallucinations, while complex hallucinations remained equivalent across the two conditions. As a result, the likelihood that an experienced hallucination was complex was higher during Ganzfeld. Despite these differences, we found a correlation between the frequency and total time spent hallucinating in Ganzflicker and Ganzfeld conditions, suggesting some shared mechanisms between the two methodologies. We attribute the tendency to experience frequent simple hallucinations in both conditions to a shared low-level core hallucinatory mechanism, such as excitability of visual cortex, potentially amplified in Ganzflicker compared to Ganzfeld due to heightened bottom-up input. The tendency to experience complex hallucinations, in contrast, may be related to top-down processes less affected by visual stimulation.

Exploring the Therapeutic Potential of Quadripulse rTMS over the Visual Cortex: A Proof-of-Concept Study in Healthy Volunteers and Chronic Migraine Patients with Medication Overuse Headache.

In chronic migraine with medication overuse (CM-MOH), sensitization of visual cortices is reflected by (i) increased amplitude of stimulus-evoked responses and (ii) habituation deficit during repetitive stimulation. Both abnormalities might be mitigated by inhibitory transcranial neurostimulation. Here, we tested an inhibitory quadripulse repetitive transcranial magnetic stimulation (rTMS-QPI) protocol to decrease durably visual cortex excitability in healthy subjects (HS) and explored its therapeutic potential in CM-MOH patients. Pattern-reversal visual evoked potentials (VEP) were used as biomarkers of effect and recorded before (T1), immediately after (T2), and 3 h after stimulation (T3). In HS, rTMS-QPI durably decreased the VEP 1st block amplitude (p < 0.05) and its habituation (p < 0.05). These changes were more pronounced for the P1N2 component that was modified already at T2 up to T3, while for N1P1 they were significant only at T3. An excitatory stimulation protocol (rTMS-QPE) tended to have an opposite effect, restricted to P1N2. In 12 CM-MOH patients, during a four-week treatment (2 sessions/week), rTMS-QPI significantly reduced monthly headache days (p < 0.01). In patients reversing from CM-MOH to episodic migraine (n = 6), VEP habituation significantly improved after treatment (p = 0.005). rTMS-QPI durably decreases visual cortex responsivity in healthy subjects. In a proof-of-concept study of CM-MOH patients, rTMS-QPI also has beneficial clinical and electrophysiological effects, but sham-controlled trials are needed.

A novel role for APP in neural circuit function

AbstractBackgroundDespite the importance of the amyloid‐precursor protein (APP) to Alzheimer’s Disease pathophysiology and therapy, and notable pan‐cellular and synaptic abundance, the physiological function of APP and its homologues remains to be fully elucidated in‐vivo. Here, we interrogated how the APP family regulates neuronal cell function and long‐range neural circuit dynamics in the intact brain.MethodAPPflox/flox/APLP2flox /flox/APLP1−/− mice were crossed with NexCre mice expressing Cre prenatally from ∼E12.5 in postmitotic neuronal precursor cells of the cortex and hippocampus, producing a conditional triple knockout model (cTKO) of the APP family in excitatory forebrain neurons that is associated with pronounced behavioral deficits (Steubler et al., 2021, EMBO Journal). Neuronal function at the single cell/unit and circuit‐level was characterised using in‐vivo two‐photon and mesoscopic calcium imaging, and bilateral Neuropixels recordings in awake and anesthetised mice.ResultcTKO mice exhibited pronounced suppression in spike timing variability and dynamic excitability in visual cortex and hippocampus CA1 relative to controls, with a marked inter‐hemispheric decoherence of oscillatory activity (including low‐frequency and sleep‐associated slow waves) and dysfunctional intrahemispheric propagation of neuronal activity. Further, cTKO mice also displayed behavioural abnormalities in open field tests relative to controls which was linked to functional deficits. High‐resolution synaptic imaging revealed a significant reduction in the number of synapses containing the NMDA receptor subunit GluN1 in cTKO mice versus controls, with partial NMDA receptor agonism (d‐cycloserine, 30mg/kg, i.p.) ameliorating cellular and circuit‐level impairments as well as behavioral impairments.ConclusionThese findings provide novel in‐vivo evidence for an essential role of APP in regulating synaptic function via an effect on NMDA receptors, that elucidate the physiological role of this preeminent protein family and have important implications for disease and therapy.

Daily rhythm in cortical chloride homeostasis underpins functional changes in visual cortex excitability

Cortical activity patterns are strongly modulated by fast synaptic inhibition mediated through ionotropic, chloride-conducting receptors. Consequently, chloride homeostasis is ideally placed to regulate activity. We therefore investigated the stability of baseline [Cl-]i in adult mouse neocortex, using in vivo two-photon imaging. We found a two-fold increase in baseline [Cl-]i in layer 2/3 pyramidal neurons, from day to night, with marked effects upon both physiological cortical processing and seizure susceptibility. Importantly, the night-time activity can be converted to the day-time pattern by local inhibition of NKCC1, while inhibition of KCC2 converts day-time [Cl-]i towards night-time levels. Changes in the surface expression and phosphorylation of the cation-chloride cotransporters, NKCC1 and KCC2, matched these pharmacological effects. When we extended the dark period by 4 h, mice remained active, but [Cl-]i was modulated as for animals in normal light cycles. Our data thus demonstrate a daily [Cl-]i modulation with complex effects on cortical excitability.

TrkB receptor-dependent PV neurons regulate visual orientation discrimination in mice

The neurotrophin-tyrosine receptor kinase B (TrkB) signaling pathway plays an important role in regulating the balance of excitation and inhibition in the primary visual cortex (V1). Previous studies have revealed its mechanism of regulating the level of cortical excitability by increasing the efficiency of excitatory transmission, but it has not been elucidated how TrkB receptors regulate the balance of excitation and inhibition through the inhibitory system, which in turn affects visual cortex function. Therefore, the objective of this study was to investigate how the TrkB signaling pathway specifically regulates the most important inhibitory neuron-PV neurons affects the visual cortex function of mice. The expression of TrkB receptor on PV neurons in the V1 region was specifically reduced by the virus, the functional changes of inhibitory and excitatory neurons in the primary visual cortex were recorded by multi-channel electrophysiological in vivo. The orientation discrimination ability of mice was tested by behavioral experiments, and altered orientation discrimination ability of mice was tested by behavioral experiments. The results showed that reduced expression of TrkB receptors on PV inhibitory neurons in primary visual cortex significantly increased the response intensity of excitatory neurons, reduced the orientation discrimination ability of inhibitory and excitatory neurons, and increased the signal-to-noise ratio, but the orientation discrimination ability at the individual level in mice showed a decrease. These results suggest that the TrkB signaling pathway does not modulate the function of PV neurons solely by increasing excitatory transmission targeting PV neurons, and its effect on neuronal signal-to-noise ratio is not due to enhancement of the inhibitory system.

Cortical excitability in human somatosensory and visual cortex: implications for plasticity and learning - a minireview.

The balance of excitation and inhibition plays a key role in plasticity and learning. A frequently used, reliable approach to assess intracortical inhibition relies on measuring paired-pulse behavior. Moreover, recent developments of magnetic resonance spectroscopy allows measuring GABA and glutamate concentrations. We give an overview about approaches employed to obtain information about excitatory states in human participants and discuss their putative relation. We summarize paired-pulse techniques and basic findings characterizing paired-pulse suppression in somatosensory (SI) and (VI) visual areas. Paired-pulse suppression describes the effect of paired sensory stimulation at short interstimulus intervals where the cortical response to the second stimulus is significantly suppressed. Simultaneous assessments of paired-pulse suppression in SI and VI indicated that cortical excitability is not a global phenomenon, but instead reflects the properties of local sensory processing. We review studies using non-invasive brain stimulation and perceptual learning experiments that assessed both perceptual changes and accompanying changes of cortical excitability in parallel. Independent of the nature of the excitation/inhibition marker used these data imply a close relationship between altered excitability and altered performance. These results suggest a framework where increased or decreased excitability is linked with improved or impaired perceptual performance. Recent findings have expanded the potential role of cortical excitability by demonstrating that inhibition markers such as GABA concentrations, paired-pulse suppression or alpha power predict to a substantial degree subsequent perceptual learning outcome. This opens the door for a targeted intervention where subsequent plasticity and learning processes are enhanced by altering prior baseline states of excitability.

The effects of estradiol levels on crossmodal perception: a study on the sound induced flash illusion in healthy and menstrually related migraine individuals

ObjectiveThe sound-induced flash illusion (SIFI) is a valid paradigm to study multisensorial perception. In the “fission” SIFI, multiple flashes are perceived when observing a single flash paired with two or more beeps. SIFI is largely dependent on visual and acoustic cortex excitability; in migraine, dysfunctional cortical excitability affects SIFI perception. Since estrogen peak occurring during ovulation can increase neuronal excitability, the present study aims to verify whether cortical excitability shifts linked to the menstrual cycle could influence SIFI.MethodsIn a comparative prospective study, we tested the effect of estrogens on crossmodal perception using the SIFI. We recruited 27 females in reproductive age, including 16 healthy and 11 menstrually related migraine females, testing their proneness to SIFI on day 14 (high estradiol) and day 27 (low estradiol) of menstrual cycle.ResultsWomen on day 14 reported less flashes than on day 27 (p = 0.02) in the fission illusion, suggesting a pro-excitatory effect of estradiol on visual cortex excitability during ovulation. Moreover, we confirmed that migraine women perceived less flashes (p = 0.001) than controls, independently from cycle phase. Non-migraineurs women significantly reported more flashes on day 27 than on day 14 (p = 0.04).ConclusionsThis study suggests that estradiol may influence the multisensory perception due to changes of visual cortex excitability, with high estradiol peak leading to increased visual cortical sensitivity during ovulation in non-migraineurs. Visual cortex hyperresponsiveness, here reflected by reduced SIFI, is not influenced by estradiol fluctuations in migraine women, as shown by reduced fission effects on day 14 and 27.

Statistical Learning of Distractor Suppression Downregulates Prestimulus Neural Excitability in Early Visual Cortex.

Visual attention is highly influenced by past experiences. Recent behavioral research has shown that expectations about the spatial location of distractors within a search array are implicitly learned, with expected distractors becoming less interfering. Little is known about the neural mechanism supporting this form of statistical learning. Here, we used magnetoencephalography (MEG) to measure human brain activity to test whether proactive mechanisms are involved in the statistical learning of distractor locations. Specifically, we used a new technique called rapid invisible frequency tagging (RIFT) to assess neural excitability in early visual cortex during statistical learning of distractor suppression while concurrently investigating the modulation of posterior alpha band activity (8-12 Hz). Male and female human participants performed a visual search task in which a target was occasionally presented alongside a color-singleton distractor. Unbeknown to the participants, the distracting stimuli were presented with different probabilities across the two hemifields. RIFT analysis showed that early visual cortex exhibited reduced neural excitability in the prestimulus interval at retinotopic locations associated with higher distractor probabilities. In contrast, we did not find any evidence of expectation-driven distractor suppression in alpha band activity. These findings indicate that proactive mechanisms of attention are involved in predictive distractor suppression and that these mechanisms are associated with altered neural excitability in early visual cortex. Moreover, our findings indicate that RIFT and alpha band activity might subtend different and possibly independent attentional mechanisms.SIGNIFICANCE STATEMENT What we experienced in the past affects how we perceive the external world in the future. For example, an annoying flashing light might be better ignored if we know in advance where it usually appears. This ability of extracting regularities from the environment is called statistical learning. In this study, we explore the neuronal mechanisms allowing the attentional system to overlook items that are unequivocally distracting based on their spatial distribution. By recording brain activity using MEG while probing neural excitability with a novel technique called RIFT, we show that the neuronal excitability in early visual cortex is reduced in advance of stimulus presentation for locations where distracting items are more likely to occur.

Modulation of top-down influence affects trafficking of glutamatergic receptors in the primary visual cortex

Numerous studies indicate that top-down influence plays critical roles in visual perception by enhancing neuronal excitability in the primary visual cortex (V1). The underlying mechanisms are poorly understood. This study examined changes of excitatory glutamatergic markers in the V1 cortex of cat after top-down influence of cortical area 7 (A7) was modulated by transcranial direct current stimulation (tDCS). Our results showed that the content of glutamate as well as the total cellular protein of glutamatergic receptors, including the key subunit GluA1 of AMPA receptors and subunit NR1 of NMDA receptors, in the V1 cortex had no significant change after anode- and cathode-tDCS relative to sham-tDCS in A7. However, the plasma membrane protein content of GluA1 and NR1 in the V1 was significantly increased after anode-tDCS, but decreased after cathode-tDCS when compared with that after sham-tDCS in A7. Further, the abundance of phosphorylated GluA1 and NR1 in the V1 also elevated significantly after anode-tDCS, but lowered after cathode-tDCS compared with that after sham-tDCS. Additionally, the content of phosphorylated CaMKII (p-CaMKII), a protein kinase preferentially boosting phosphorylation of glutamatergic receptors, in the V1 improved after anode-tDCS although no significant alteration occurred after c-tDCS in A7. Taken together, our results indicate that feedback influence of A7 may facilitate the trafficking of glutamatergic receptors to postsynaptic membrane in the V1 cortex through receptors’ phosphorylation process, which could be an important mechanism of high-level cortex in modulating visual information processing in the V1 cortex.

Anticipatory attention is a stable state induced by transient control mechanisms.

Anticipatory attention is a neurocognitive state in which attention control regions bias neural activity in sensory cortical areas to facilitate the selective processing of incoming targets. Previous electroencephalographic (EEG) studies have identified event-related potential (ERP) signatures of anticipatory attention, and implicated alpha band (8–12 Hz) EEG oscillatory activity in the selective control of neural excitability in visual cortex. However, the degree to which ERP and alpha band measures reflect related or distinct underlying neural processes remains to be further understood. To investigate this question, we analyzed EEG data from 20 human participants performing a cued object-based attention task. We used support vector machine (SVM) decoding analysis to compare the attentional time courses of ERP signals and alpha band power. We found that ERP signals encoding attentional instructions are dynamic and precede stable attention-related changes in alpha power, suggesting that ERP and alpha power reflect distinct neural processes. We proposed that the ERP patterns reflect transient attentional orienting signals originating in higher order control areas, whereas the patterns of synchronized oscillatory neural activity in the alpha band reflect a sustained attentional state. These findings support the hypothesis that anticipatory attention involves transient top-down control signals that establish more stable neural states in visual cortex, enabling selective sensory processing.

Expectance of low contrast retro-cues does not modulate anticipatory alpha power

It has been proposed that alpha oscillations reflect the endogenous modulation of visual cortex excitability. In particular, alpha power increases during the maintenance period in Working Memory (WM) tasks have been interpreted as a mechanism to avoid potential interference of incoming stimuli. In this study we tested whether alpha power was modulated during the maintenance of WM to enhance the processing of relevant incoming perceptual stimuli. To this aim, we manipulated the contrast of a stimulus presented during the maintenance period of a WM task. The to-be-detected stimulus could indicate which of the encoded representations was going to be probed after the delay (spatial retro-cue) or could signal that all the representations had equal probability to be tested (neutral retro-cue). Time-frequency analysis revealed that alpha power preceding retro-cue presentation was not differently modulated by the two different contrast conditions. This is, participants did not endogenously modulate alpha oscillations upon low perceptual contrast stimuli incoming. These results suggest that alpha delay activity is not a goal directed mechanism to control the inflow of information during WM maintenance. Instead, current data suggest that alpha delayed activity might be an index of increased allocation of attentional resources to the processing of the WM representations.

TACS phase-specifically biases brightness perception of flickering light

BackgroundVisual phenomena like brightness illusions impressively demonstrate the highly constructive nature of perception. In addition to physical illumination, the subjective experience of brightness is related to temporal neural dynamics in visual cortex. ObjectiveHere, we asked whether biasing the temporal pattern of neural excitability in visual cortex by transcranial alternating current stimulation (tACS) modulates brightness perception of concurrent rhythmic visual stimuli. MethodsParticipants performed a brightness discrimination task of two flickering lights, one of which was targeted by same-frequency electrical stimulation at varying phase shifts. tACS was applied with an occipital and a periorbital active control montage, based on simulations of electrical currents using finite element head models. ResultsExperimental results reveal that flicker brightness perception is modulated dependent on the phase shift between sensory and electrical stimulation, solely under occipital tACS. Phase-specific modulatory effects by tACS were dependent on flicker-evoked neural phase stability at the tACS-targeted frequency, recorded prior to electrical stimulation. Further, the optimal timing of tACS application leading to enhanced brightness perception was correlated with the neural phase delay of the cortical flicker response. ConclusionsOur results corroborate the role of temporally coordinated neural activity in visual cortex for brightness perception of rhythmic visual input in humans. Phase-specific behavioral modulations by tACS emphasize its efficacy to transfer perceptually relevant temporal information to the cortex. These findings provide an important step towards understanding the basis of visual perception and further confirm electrical stimulation as a tool for advancing controlled modulations of neural activity and related behavior.

Removal of Perineuronal Nets Leads to Altered Neuronal Excitability and Synaptic Transmission in Visual Cortex with Distinct Time Courses

Removal of Perineuronal Nets Leads to Altered Neuronal Excitability and Synaptic Transmission in Visual Cortex with Distinct Time Courses

Deficits in central auditory processing among migraine patients

BackgroundMigraine is a neurological disease associated with abnormal excitability in visual, somatosensory, and motor cortex. This study aimed to verify and compare auditory processing performance in migraine patients with and without dizziness and healthy controls.ResultsSixty subjects were divided into 3 groups: control group, twenty normal healthy subjects, and study group I (twenty subjects diagnosed with migraine) and study group II (twenty subjects diagnosed with vestibular migraine). They were evaluated using the Central Auditory Processing Questionnaire for adults, tympanometry, pure tone audiometry, Psychophysical Central Auditory Tests, including Arabic Speech Intelligibility in Noise Test for adults, Arabic Dichotic Digit Test [version II], Gap in Noise Test, Duration Pattern Test, and Arabic Memory Tests. No significant difference was found between the two study groups I and II, but the significant difference was found between the study groups and the control group in all central auditory test results. Statistically significant difference was found between the control group and study groups I and II regarding all memory tests. The highest percentage of abnormality was present in temporal resolution and selective auditory attention in both study groups. There was no significant statistical correlation between the number of attacks/month and central auditory test results. There was no significant statistical correlation between the frequency of attacks in VM patients and central auditory test results.ConclusionsPatients with migraine and vestibular migraine had an inferior performance in all psychophysical central auditory tests when compared with control. Also, there was no significant difference between the 2 study groups regarding central auditory test results which may support that both migraine with and without dizziness have the same pathophysiology.

Evaluation Of Central Auditory Function In Migraine Patients

Abstract Background Migraine is a neurological disease associated with abnormal excitability in visual, somatosensory and motor cortex. Previous researches reported abnormalities in the auditory brainstem response (ABR) and in vestibular functions. These results are an indicator of impending auditory malfunction in Migraine and disruption of central auditory processing mechanisms. Objectives This study aimed to assess and compare central auditory processing (CAP) performance in migraine patients with and without dizziness and healthy controls. Subjects and method Sixty subjects aged between18 and 60 years divided into 3 groups; control group (twenty normal healthy subjects), study group I (twenty subject diagnosed with migraine) and study group II (twenty subjects diagnosed with vestibular migraine). They were subjected to a headache sheet, central auditory processing questionnaire and Psychophysical central auditory tests: including Arabic Speech Intelligibility In Noise (SPIN) test for adults, Arabic Dichotic digit test, Gap In Noise (GIN) test, Duration pattern test and Arabic memory tests. Results Statistically significant difference was found between the 2 study groups and control group regarding right dichotic (p = 0.004),right and left duration pattern tests (p = 0.01) with highly statistically significant difference(p &amp;lt; 0.001) Gap In Noise (GIN) test, left dichotic digit test, right and left speech in noise. But there was no statistically significant difference between the two study groups regarding all tests. Conclusions Patients with migraine and vestibular migraine had poor performance in all central auditory tests when compared with control this mean that migraine lead to impaired central auditory processing in adults. Also, there was no significant difference between the 2 study groups regarding central auditory test results which may support that both migraine with and without dizziness have the same pathophysiology.

Onabotulinumtoxina reduce visual cortical excitability in chronic migraine: Preliminary results of a study with sound induced flash illusions

The number of sound-induced flash illusions (SIFI) perceived are related with the level of visual cortex (V1) excitability. In episodic migraineurs, in response to visual-acoustic illusions, V1 is hyperexcitable. The injection of botulinum toxin type A was approved as a therapy for chronic migraine (CM). Recent studies have correlated the action of botulinum toxin with the release of CGRP and cortical excitability. We used SIFI to evaluate the V1 excitability in CM at baseline and 3 months after treatment with botulinum toxin.

Magnetic Suppression of Perceptual Accuracy Is Not Reduced in Visual Snow Syndrome

Objective: Patients with visual snow syndrome (VSS) suffer from continuous (“TV snow-like”) visual disturbance of unknown pathoetiology. In VSS, changes in cortical excitability in the primary visual cortex and the visual association cortex are discussed, with recent imaging studies tending to point to higher-order visual areas. Migraine, especially migraine with aura, is a common comorbidity. In chronic migraine and episodic migraine with aura but not in episodic migraine without aura, a reduced magnetic suppression of perceptual accuracy (MSPA) reflects a probably reduced inhibition of the primary visual cortex. Here we investigated the inhibition of the primary visual cortex using MSPA in patients with VSS, comparing that with MSPA in controls matched for episodic migraine.Methods: Seventeen patients with VSS were compared to 17 age- and migraine-matched controls. Visual accuracy was assessed by letter recognition and modulated by transcranial magnetic stimulation delivered to the occipital cortex at different intervals with respect to the letter presentation (40, 100, and 190 ms).Results: Suppression of visual accuracy at the 100-ms interval was present without significant differences between VSS patients and age- and migraine-matched controls (percentage of correctly recognized trigrams, control: 46.4 ± 34.3; VSS: 52.5 ± 25.4, p = 0.56).Conclusions: In contrast to migraine with aura, occipital cortex inhibition, as assessed with MSPA, may not be affected in VSS.

Top-down control of visual cortex by the frontal eye fields through oscillatory realignment

Voluntary allocation of visual attention is controlled by top-down signals generated within the Frontal Eye Fields (FEFs) that can change the excitability of lower-level visual areas. However, the mechanism through which this control is achieved remains elusive. Here, we emulated the generation of an attentional signal using single-pulse transcranial magnetic stimulation to activate the FEFs and tracked its consequences over the visual cortex. First, we documented changes to brain oscillations using electroencephalography and found evidence for a phase reset over occipital sites at beta frequency. We then probed for perceptual consequences of this top-down triggered phase reset and assessed its anatomical specificity. We show that FEF activation leads to cyclic modulation of visual perception and extrastriate but not primary visual cortex excitability, again at beta frequency. We conclude that top-down signals originating in FEF causally shape visual cortex activity and perception through mechanisms of oscillatory realignment.

Parallel modulation of intracortical excitability of somatosensory and visual cortex by the gonadal hormones estradiol and progesterone

The levels of the gonadal hormones estradiol and progesterone vary throughout the menstrual cycle thereby affecting cognition, emotion, mood, and social behaviour. However, how these hormones modulate the balance of neural excitation and inhibition, which crucially regulate processing and plasticity, is not fully understood. We here used paired-pulse stimulation to investigate in healthy humans the action of low and high estradiol and progesterone on intracortical inhibition in somatosensory (SI) and visual cortex (V1). We found that paired-pulse suppression in both SI and VI depended on estradiol. During high estradiol levels, paired-pulse suppression was significantly reduced. No comparable effects were found for progesterone, presumably due to a confounding effect of estradiol. Also, no hormone level-depending effects were observed for single-pulse evoked SEPs (somatosensory evoked potentials) and VEPs (visual evoked potentials) indicating a specific hormonal action on intracortical processing. The results demonstrate that estradiol globally modulates the balance of excitation and inhibition of SI and VI cortex.