Causal topography of visual cortex in perceptual learning.

Individuals are able to improve their visual skill with practice, a phenomenon called Visual Perceptual Learning (VPL). We previously observed that after training on a difficult shape identification task, the dorsal visual regions (i.e. right V2d/V3 and right lateral occipital, LO) corresponding to the trained visual quadrant, and their homologous in the opposite hemisphere, exhibited a selective activation at the end of the learning. By contrast, such modulation was not observed in the ventral visual regions, corresponding to the untrained quadrants. The causal role of the trained visual cortex was previously showed in a TMS study as its inactivation impaired behavioral performance to learned stimuli. Here, using the same experimental design, we employed TMS over the homologous of the trained area (i.e. left V2d/V3) as well as over the untrained region (i.e. right V4) to causally map the visual network during the perceptual learning. We report a decrease of accuracy after TMS over left V2d/V3 as compared to both right V4 and Sham (inactive stimulation) conditions. Importantly, TMS effect was correlated with the degree of learning, such that subjects with lower accuracy at the end of the training exhibited stronger TMS impairment. These results provide evidence that segregated regions within the visual network are causally involved in visual perceptual learning

Resting-state modulation of alpha rhythms by interference with angular gyrus activity

The default mode network is active during restful wakefulness and suppressed during goal-driven behavior. We hypothesize that inhibitory interference with spontaneous ongoing, that is, not task-driven, activity in the angular gyrus (AG), one of the core regions of the default mode network, will enhance the dominant idling EEG alpha rhythms observed in the resting state. Fifteen right-handed healthy adult volunteers underwent to this study. Compared with sham stimulation, magnetic stimulation (1 Hz for 1 min) over both left and right AG, but not over FEF or intraparietal sulcus, core regions of the dorsal attention network, enhanced the dominant alpha power density (8-10 Hz) in occipitoparietal cortex. Furthermore, right AG-rTMS enhanced intrahemispheric alpha coherence (8-10 Hz). These results suggest that AG plays a causal role in the modulation of dominant low-frequency alpha rhythms in the resting-state condition

Electrophysiological correlates of stimulus-driven reorienting deficits after interference with right parietal cortex during a spatial attention task: A TMS-EEG study

TMS interference over right intraparietal sulcus (IPS) causally disrupts behaviorally and EEG rhythmic correlates of endogenous spatial orienting before visual target presentation [Capotosto, P., Babiloni, C., Romani, G. L., & Corbetta, M. Differential contribution of right and left parietal cortex to the control of spatial attention: A simultaneous EEG-rTMS study. Cerebral Cortex, 22, 446-454, 2012; Capotosto, P., Babiloni, C., Romani, G. L., & Corbetta, M. Fronto-parietal cortex controls spatial attention through modulation of anticipatory alpha rhythms. Journal of Neuroscience, 29, 5863-5872, 2009]. Here we combine data from our previous studies to examine whether right parietal TMS during spatial orienting also impairs stimulus-driven reorienting or the ability to efficiently process unattended stimuli, that is, stimuli outside the current focus of attention. Healthy volunteers (n = 24) performed a Posner spatial cueing task while their EEG activity was being monitored. Repetitive TMS (rTMS) was applied for 150 msec simultaneously to the presentation of a central arrow directing spatial attention to the location of an upcoming visual target. Right IPS-rTMS impaired target detection, especially for stimuli presented at unattended locations; it also caused a modulation of the amplitude of parieto-occipital positive ERPs peaking at about 480 msec (P3) post-target. The P3 significantly decreased for unattended targets and significantly increased for attended targets after right IPS-rTMS as compared with sham stimulation. Similar effects were obtained for left IPS stimulation albeit in a smaller group of volunteers. We conclude that disruption of anticipatory processes in right IPS has prolonged effects that persist during target processing. The P3 decrement may reflect interference with postdecision processes that are part of stimulus-driven reorienting. Right IPS is a node of functional interaction between endogenous spatial orienting and stimulus-driven reorienting processes in human vision

Dynamics of EEG rhythms support distinct visual selection mechanisms in parietal cortex: A simultaneous transcranial magnetic stimulation and EEG study

Using repetitive transcranial magnetic stimulation (rTMS), we have recently shown a functional anatomical distinction in human parietal cortex between regions involved in maintaining attention to a location [ventral intraparietal sulcus (vIPS)] and a region involved in shifting attention between locations [medial superior parietal lobule (mSPL)]. In particular, while rTMS interference over vIPS impaired target discrimination at contralateral attended locations, interference over mSPL affected performance following shifts of attention regardless of the visual field (Capotosto et al., 2013). Here, using rTMS interference in conjunction with EEG recordings of brain rhythms during the presentation of cues that indicate to either shift or maintain spatial attention, we tested whether this functional anatomical segregation involves different mechanisms of rhythm synchronization. The transient inactivation of vIPS reduced the amplitude of the expected parieto-occipital low-alpha (8 - 10 Hz) desynchronization contralateral to the cued location. Conversely, the transient inactivation of mSPL, compared with vIPS, reduced the high-alpha (10 - 12 Hz) desynchronization induced by shifting attention into both visual fields. Furthermore, rTMS induced a frequency-specific delay of task-related modulation of brain rhythms. Specifically, rTMS over vIPS or mSPL during maintenance (stay cues) or shifting (shift cues) of spatial attention, respectively, caused a delay of alpha parieto-occipital desynchronization. Moreover, rTMS over vIPS during stay cues caused a delay of delta (2-4 Hz) frontocentral synchronization. These findings further support the anatomo-functional subdivision of the dorsal attention network in subsystems devoted to shifting or maintaining covert visuospatial attention and indicate that these mechanisms operate in different frequency channels linking frontal to parieto-occipital visual regions

Anatomical segregation of visual selection mechanisms in human parietal cortex

none8siVisual selection requires mechanisms for representing object salience and for shifting the focus of processing to novel objects. It is not clear from computational or neural models whether these operations are performed within the same or different brain regions. Here, we use repetitive transcranial magnetic stimulation to briefly interfere with neural activity in individually localized regions of human posterior parietal cortex (PPC) that are putatively involved in attending to contralateral locations or shifting attention between locations. Stimulation over right ventral intraparietal sulcus impaired target discrimination at contralateral locations, whereas stimulation over right medial superior parietal lobule impaired target discrimination after a shift of attention regardless of its location. This double dissociation is consistent with neuroimaging studies and indicates that mechanisms of visual selection are partly anatomically segregated in human PPC.mixedCapotosto, Paolo; Tosoni, Annalisa; Spadone, Sara; Sestieri, Carlo; Perrucci, Mauro Gianni; Romani, Gian Luca; Della Penna, Stefania; Corbetta, MaurizioCapotosto, Paolo; Tosoni, Annalisa; Spadone, Sara; Sestieri, Carlo; Perrucci, Mauro Gianni; Romani, Gian Luca; Della Penna, Stefania; Corbetta, Maurizi

Visuo-spatial attention and semantic memory competition in the parietal cortex

Abstract Neuroimaging studies associate specific functional roles to distinct brain regions investigating separate cognitive processes using dedicated tasks. For example, using both correlative (i.e., fMRI) and causal (i.e., TMS) approaches it has been shown the involvement of intra-parietal sulcus (IPS), as part of the dorsal attention network, in spatial attentional tasks as well as the importance of the angular gyrus (AG), as part of the default mode network, during the selection of relevant information in semantic memory. Nonetheless, in our daily life attention and semantic memory are rarely needed in isolation. In the present TMS study we investigate how the brain combines attentional and semantic memory demands in a single task. Results showed that, compared to a pseudo-TMS, stimulation of IPS, but not AG, affects behavioral performance, thus suggesting its preponderant role in such a combined task. Moreover, the lack of difference between the effect of IPS and AG stimulations seems to suggest that the two regions may be coactivated or that a third-party source might indirectly mediate the interaction between the two networks