Occipital Cortex of Blind Individuals Is Functionally Coupled with Executive Control Areas of Frontal Cortex

In congenital blindness, the occipital cortex responds to a range of nonvisual inputs, including tactile, auditory, and linguistic stimuli. Are these changes in functional responses to stimuli accompanied by altered interactions with nonvisual functional networks? To answer this question, we introduce a data-driven method that searches across cortex for functional connectivity differences across groups. Replicating prior work, we find increased fronto-occipital functional connectivity in congenitally blind relative to blindfolded sighted participants. We demonstrate that this heightened connectivity extends over most of occipital cortex but is specific to a subset of regions in the inferior, dorsal, and medial frontal lobe. To assess the functional profile of these frontal areas, we used an n-back working memory task and a sentence comprehension task. We find that, among prefrontal areas with overconnectivity to occipital cortex, one left inferior frontal region responds to language over music. By contrast, the majority of these regions responded to working memory load but not language. These results suggest that in blindness occipital cortex interacts more with working memory systems and raise new questions about the function and mechanism of occipital plasticity.David & Lucile Packard FoundationNational Science Foundation (U.S.). Graduate Research Fellowship Progra

Evidence for Extreme Cortical Flexibility: Higher Cognitive Functions in "Visual" Cortices of Blind Individuals

Are structure and function inextricably linked in the brain? In the early 19th century, phrenologists endeavored to localize cognition to areas of the brain. Though neuroscientists have updated the methodology and the notion of what constitutes a mental process, the goal remains the same: to map functions to locations. But how flexible are these structure-to- function mappings? Studying adaptations of the “visual” cortex to blindness offers insight on the extent to which brain structures can carry out functions for which they did not evolve. In this dissertation, I ask how flexible visual cortices are in the absence of expected visual information. I examine the ability of blind individuals’ occipital cortices to take on functions that are higher cognitive and, therefore, radically different from vision. First, Chapter 2 explores the extent of higher cognitive takeover of “visual” cortices in blindness. Using naturalistic stimuli, I find that “visual” cortices of blind individuals synchronize to a shared interpretive, rather than a shared perceptual, experience. This suggests systematic and widespread repurposing of “visual” cortices for higher-cognitive functions. Next, Chapter 3 asks whether “visual” cortices of blind individuals are repurposed for higher cognitive functions other than language, and executive functions in particular. I find evidence for executive functions in primarily right-lateralized “visual” cortices using both a non-verbal response-inhibition task and by examining functional connectivity at rest. Finally, Chapter 4 examines the functional relevance of previously observed language and executive function responses in the “visual” cortices of blind individuals. I find that blind individuals are better than matched sighted controls at comprehending syntactically complex sentences and at inhibiting prepotent button pressing. This suggests that repurposed “visual” cortices may confer a behavioral advantage. Taken together, this dissertation demonstrates that “visual” cortices of blind individuals are meaningfully repurposed for higher cognitive functions. Though brain structures may seem particularly suited to implement a particular function, such structure- to-function mappings are not evidence of functional rigidity. In contrast, evidence from blindness suggests that human cortex is highly flexible at birth

Pinpointing a highly specific pathological functional connection that turns phantom sound into distress

International audienceIt has been suggested that an auditory phantom percept is the result of multiple, parallel but overlapping networks. One of those networks encodes tinnitus loudness and is electrophysiologically separable from a non-specific distress network. The present study investigates how these networks anatomically overlap, what networks are involved and how and when these networks interact. The EEG data of 317 tinnitus patients and 256 healthy subjects were analyzed, using independent component analysis. Results demonstrate that tinnitus is characterized by at least two major brain networks, each consisting of multiple independent components. One network reflects tinnitus distress, while another network reflects the loudness of the tinnitus. The component coherence analysis shows that the independent components that make up the distress and loudness networks communicate within their respective network at several discrete frequencies in parallel. The distress and loudness networks do not intercommunicate for patients without distress, but do when patients are distressed by their tinnitus. The obtained data demonstrate that the components that build up these two separable networks communicate at discrete frequencies within the network, and only between the distress and loudness networks in those patients in whom the symptoms are also clinically linked

Preservation and plasticity in the neural basis of numerical thinking in blindness

Numerical reasoning pervades modern human culture and depends on a fronto-parietal network, a key node of which is the intraparietal sulcus (IPS). In this dissertation I investigate how visual experience shapes the cognitive and neural basis of numerical thinking by studying numerical cognition in congenitally blind individuals. In Chapter 2, I ask how the cognitive basis of numerical thinking is shaped by visual experience. I test whether the precision of approximate number representations develops normally in the absence of vision and test whether the relationship between numerical approximation and math abilities is preserved in congenital blindness. In Chapter 3, I ask how the neural basis of symbolic number reasoning is modified by visual experience by studying neural responses to symbolic math in congenitally blind individuals. This initial investigation revealed that the fronto-parietal number system is preserved in blindness but that some “visual” cortices are recruited for symbolic number processing in blindness. The following chapters unpack these two patterns preservation and plasticity. In Chapter 4, I use resting-state data to ask whether functional connectivity with higher-cognitive networks is a potential mechanism by which “visual” cortices are reorganized in blindness. In Chapter 5, I work with individuals who became blind as adults to determine whether visual cortex plasticity for numerical functions is possible in the adult cortex or whether it is restricted to sensitive periods in development. In Chapter 6, I investigated whether the IPS and newly identified number-responsive “visual” area of congenitally blind individuals possess population codes that distinguish between different quantities. I find that the behavioral signatures of numerical reasoning are indistinguishable across congenitally blind and sighted groups and that the fronto-parietal number network, in particular the IPS, is preserved in the absence of vision. A dorsal occipital region showed the same functional profile as the IPS number system in congenitally blind individuals. Number-related plasticity was restricted to a sensitive period in development as it was not observed in adult-onset blind individuals. Furthermore, in congenital blindness, sub-specialization of the “visual” cortex for math and language processing followed the functional connectivity patterns of “visual” cortex

Resting-state abnormalities in heroin-dependent individuals

Drug addiction is a major health problem worldwide. Recent neuroimaging studies have shed light into the underlying mechanisms of drug addiction as well as its consequences to the human brain. The most vulnerable, to heroin addiction, brain regions have been reported to be specific prefrontal, parietal, occipital, and temporal regions, as well as, some subcortical regions. The brain regions involved are usually linked with reward, motivation/drive, memory/learning, inhibition as well as emotional control and seem to form circuits that interact with each other. So, along with neuroimaging studies, recent advances in resting-state dynamics might allow further assessments upon the multilayer complexity of addiction. In the current manuscript, we comprehensively review and discuss existing resting-state neuroimaging findings classified into three overlapping and interconnected groups: functional connectivity alterations, structural deficits and abnormal topological properties. Moreover, behavioral traits of heroin-addicted individuals as well as the limitations of the currently available studies are also reviewed. Finally, in need of a contemporary therapy a multimodal therapeutic approach is suggested using classical treatment practices along with current neurotechonologies, such as neurofeedback and goal-oriented video-games

Functional connectivity of brain networks with three monochromatic wavelengths: a pilot study using resting-state functional magnetic resonance imaging

Exposure to certain monochromatic wavelengths can affect non-visual brain regions. Growing research indicates that exposure to light can have a positive impact on health-related problems such as spring asthenia, circadian rhythm disruption, and even bipolar disorders and Alzheimer’s. However, the extent and location of changes in brain areas caused by exposure to monochromatic light remain largely unknown. This pilot study (N = 7) using resting-state functional magnetic resonance shows light-dependent functional connectivity patterns on brain networks. We demonstrated that 1 min of blue, green, or red light exposure modifies the functional connectivity (FC) of a broad range of visual and non-visual brain regions. Largely, we observed: (i) a global decrease in FC in all the networks but the salience network after blue light exposure, (ii) a global increase in FC after green light exposure, particularly noticeable in the left hemisphere, and (iii) a decrease in FC on attentional networks coupled with a FC increase in the default mode network after red light exposure. Each one of the FC patterns appears to be best arranged to perform better on tasks associated with specific cognitive domains. Results can be relevant for future research on the impact of light stimulation on brain function and in a variety of health disciplines.Peer ReviewedPostprint (author's final draft

Neural correlates of visual awareness

openL'elaborato si propone di esporre le attuali evidenze riguardanti il modo in cui i contenuti soggettivi di consapevolezza visiva sono codificati a livello neurale. Sebbene i meccanismi neurali della percezione visiva siano ampiamente conosciuti, rimane ancora da chiarire come l'informazione visiva entri a far parte dei contenuti della coscienza. Per identificare i correlati neurali della coscienza (CNC), che rappresentano la minima attività neurale per una specifica esperienza conscia, vengono messe in relazione misure comportamentali di consapevolezza, limitatamente a stimoli presentati in un contesto sperimentale, con i sottostanti meccanismi neurali. Attraverso paradigmi sperimentali come la rivalità binoculare e tecniche di mascheramento visivo è possibile provare ad identificare i CNC contenuto-specifici utilizzando misure neurofisiologiche e tecniche di neuroimaging. Tali tecniche forniscono infatti utili informazioni circa le basi neuroanatomiche e funzionali dell'esperienza sotto esame. Sebbene i meccanismi che sottendono l’attenzione siano spesso associati all'esperienza cosciente, evidenze sperimentali suggeriscono una separazione tra i due processi. Le ricerche sui correlati neurali della consapevolezza visiva indicano come l’attività di una singola area cerebrale non possa essere necessaria e sufficiente a spiegare le qualità dei contenuti coscienti. Sembrerebbe invece essere necessaria una rappresentazione della scena visiva distribuita nella corteccia visiva primaria (V1) e nelle aree visive ventrali con attivazione di regioni temporo-parietali. Misure elettrofisiologiche come la visual awareness negativity (VAN) sono state correlate alla consapevolezza visiva mentre altri indicatori sembrerebbero essere maggiormente legati a processi attentivi. Diversi modelli teorici offrono spiegazioni empiriche sull’emergenza della coscienza dall’attività cerebrale. Nel caso della consapevolezza visiva, alcuni modelli teorici rilevanti sono la teoria dello spazio di lavoro neurale globale, la quale sottolinea la necessità di condivisione dell'informazione tra ampie aree cerebrali e la teoria dell'elaborazione ricorrente che si concentra invece sul feedback proveniente a V1 dalle aree extrastriate. Inoltre, il modello dell’”elaborazione predittiva” descrive la percezione cosciente come il risultato di un processo attivo in cui il cervello crea costantemente previsioni sull’ambiente circostante. Allo stato attuale, la ricerca sui correlati neurali della consapevolezza visiva evidenzia dunque come un network di regioni cerebrali posteriori sia fondamentale per avere esperienze visive coscienti. Inoltre, i segnali di feedback sembrano svolgere un ruolo cruciale, evidenziando le complesse interazioni tra dinamiche neurali e percezione cosciente.The paper aims to present the current evidence regarding how subjective contents of visual awareness are encoded at the neural level. While the neural mechanisms of visual perception are well understood, it remains unclear how visual information becomes part of consciousness. To identify the neural correlates of consciousness (NCC), representing the minimum neural activity for a specific conscious experience, behavioral measures of awareness are related to underlying neural mechanisms, limited to stimuli presented in an experimental context. Through experimental paradigms such as binocular rivalry and visual masking techniques, it is possible to attempt to identify content-specific NCC using neurophysiological measures and neuroimaging techniques. These techniques indeed provide valuable information about the neuroanatomical and functional basis of the examined experience. Although mechanisms underlying attention are often associated with conscious experience, experimental evidence suggests a separation between the two processes. Research on the neural correlates of visual awareness indicates that the activity of a single brain area may not be necessary and sufficient to explain the qualities of conscious contents. Instead, a distributed representation of the visual scene in the primary visual cortex (V1) and ventral visual areas with activation of temporo-parietal regions seems to be necessary. Electrophysiological measures such as Visual Awareness Negativity (VAN) have been correlated with visual awareness, while other indicators appear to be more related to attentional processes. Various theoretical models offer empirical explanations of the emergence of consciousness from brain activity. In the case of visual awareness, some relevant theoretical models include the global neural workspace theory, which emphasizes the need for information sharing among extensive brain areas, and the recurrent processing theory, which focuses on feedback from extrastriate areas to V1. Additionally, the predictive processing model describes conscious perception as the result of an active process in which the brain constantly generates predictions about the surrounding environment. Currently, research on the neural correlates of visual awareness highlights the importance of a network of posterior brain regions for conscious visual experiences. Furthermore, feedback signals appear to play a crucial role, highlighting the complex interactions between neural dynamics and conscious perception