Propagated infra-slow intrinsic brain activity reorganizes across wake and slow wave sleep

Propagation of slow intrinsic brain activity has been widely observed in electrophysiogical studies of slow wave sleep (SWS). However, in human resting state fMRI (rs-fMRI), intrinsic activity has been understood predominantly in terms of zero-lag temporal synchrony (functional connectivity) within systems known as resting state networks (RSNs). Prior rs-fMRI studies have found that RSNs are generally preserved across wake and sleep. Here, we use a recently developed analysis technique to study propagation of infra-slow intrinsic blood oxygen level dependent (BOLD) signals in normal adults during wake and SWS. This analysis reveals marked changes in propagation patterns in SWS vs. wake. Broadly, ordered propagation is preserved within traditionally defined RSNs but lost between RSNs. Additionally, propagation between cerebral cortex and subcortical structures reverses directions, and intra-cortical propagation becomes reorganized, especially in visual and sensorimotor cortices. These findings show that propagated rs-fMRI activity informs theoretical accounts of the neural functions of sleep

Measuring working memory load effects on electrophysiological markers of attention orienting during a simulated drive

Intersection accidents result in a significant proportion of road fatalities, and attention allocation likely plays a role. Attention allocation may depend on (limited) working memory (WM) capacity. Driving is often combined with tasks increasing WM load, consequently impairing attention orienting. This study (n = 22) investigated WM load effects on event-related potentials (ERPs) related to attention orienting. A simulated driving environment allowed continuous lane-keeping measurement. Participants were asked to orient attention covertly towards the side indicated by an arrow, and to respond only to moving cars appearing on the attended side by pressing a button. WM load was manipulated using a concurrent memory task. ERPs showed typical attentional modulation (cue: contralateral negativity, LDAP; car: N1, P1, SN and P3) under low and high load conditions. With increased WM load, lane-keeping performance improved, while dual task performance degraded (memory task: increased error rate; orienting task: increased false alarms, smaller P3). Practitioner Summary: Intersection driver-support systems aim to improve traffic safety and flow. However, in-vehicle systems induce WM load, increasing the tendency to yield. Traffic flow reduces if drivers stop at inappropriate times, reducing the effectiveness of systems. Consequently, driver-support systems could include WM load measurement during driving in the development phase

Neural dynamics of visual awareness investigated by means of Fast Optical Imaging and EEG

The search for the Neural Correlate of Consciousness (NCC, Koch, 2004) is one of the unresolved problems of cognitive neuroscience. Although great efforts have been made to seek to answer this fundamental question, theories about the neural basis of consciousness provide different and competing answers. The heterogeneity of the NCCs interpretations could be due to a methodological gap since so far studies trying to unveil the neural correlates of visual awareness have employed techniques that can reach a high level of resolution only in one dimension (i.e., space or time) resulting to be inadequate to investigate the spatio-temporal dynamics related to conscious vision. The following studies aim to elucidate the controversial search for the neural correlates of visual awareness, by proposing innovative and cutting-edge approaches that allow to move beyond these issues. In the first study, availing of EEG and EROS (Event-Related Optical Signal) techniques we seek to unravel the spatio-temporal dynamics occurring when a visual stimulus enters consciousness. To do so, participants’ brain activity is recorded during the performance of a discrimination task by means of EEG and EROS in separate sessions. EEG allows to investigate the electrophysiological correlates of visual awareness and to identify their exact timing, while EROS permits to disentangle which brain regions and in what order of activation are involved when the stimulus is reported as consciously perceived. Results revealed that when the stimulus entered the consciousness, it elicited a sustained activation in LOC, suggesting that this brain region could represent a reliable neural correlate of consciousness. Interestingly, this sustained activation occurred within the temporal window of VAN (Visual Awareness Negativity), corroborating the idea that LOC could serve as the cortical generator of VAN, which is typically considered a reliable marker of conscious vision. In the second study, EEG signal was decomposed into maximally independent components by means of ICA (Independent Component Analysis) in order to unveil the cortical generators and the time-courses of independent neural sources that significantly contribute to the ERP correlates of visual awareness (i.e., Visual Awareness Negativity and Late Positivity). It emerged that the neural sources of VAN seem to be localized in posterior brain regions, including occipital and temporal cortex, while LP seems to reflect a combination of multiple sources spread over frontal, parietal and occipito-temporal cortex. Overall, the present results provide innovative insights into the search for the neural correlates of visual awareness

Neural Correlates of Auditory Perceptual Awareness and Release from Informational Masking Recorded Directly from Human Cortex: A Case Study.

In complex acoustic environments, even salient supra-threshold sounds sometimes go unperceived, a phenomenon known as informational masking. The neural basis of informational masking (and its release) has not been well-characterized, particularly outside auditory cortex. We combined electrocorticography in a neurosurgical patient undergoing invasive epilepsy monitoring with trial-by-trial perceptual reports of isochronous target-tone streams embedded in random multi-tone maskers. Awareness of such masker-embedded target streams was associated with a focal negativity between 100 and 200 ms and high-gamma activity (HGA) between 50 and 250 ms (both in auditory cortex on the posterolateral superior temporal gyrus) as well as a broad P3b-like potential (between ~300 and 600 ms) with generators in ventrolateral frontal and lateral temporal cortex. Unperceived target tones elicited drastically reduced versions of such responses, if at all. While it remains unclear whether these responses reflect conscious perception, itself, as opposed to pre- or post-perceptual processing, the results suggest that conscious perception of target sounds in complex listening environments may engage diverse neural mechanisms in distributed brain areas

Early Neural Markers of Implicit Attitudes: N170 Modulated by Intergroup and Evaluative Contexts in IAT

The Implicit Association Test (IAT) is the most popular measure to evaluate implicit attitudes. Nevertheless, its neural correlates are not yet fully understood. We examined event related potentials (ERPs) in response to face- and word processing while indigenous and non-indigenous participants performed an IAT displaying faces (ingroup and outgroup members) and words (positive and negative valence) as targets of category judgments. The N170 component was modulated by valence of words and by ingroup/outgroup face categorization. Contextual effects (face–words implicitly associated in the task) had an influence on the N170 amplitude modulation. On the one hand, in face categorization, right N170 showed differences according to the association between social categories of faces and affective valence of words. On the other, in word categorization, left N170 presented a similar modulation when the task implied a negative-valence associated with ingroup faces. Only indigenous participants showed a significant IAT effect and N170 differences. Our results demonstrate an early ERP blending of stimuli processing with both intergroup and evaluative contexts, suggesting an integration of contextual information related to intergroup attitudes during the early stages of word and face processing. To our knowledge, this is the first report of early ERPs during an ethnicity IAT, opening a new branch of exchange between social neuroscience and social psychology of attitudes

Face recognition deficits in a patient with Alzheimer's Disease: amnesia or agnosia? The importance of electrophysiological markers for differential diagnosis

Face recognition deficits are frequently reported in Alzheimer's disease (AD) and often attributed to memory impairment. However, it has been hypothesized that failure in identifying familiar people could also be due to deficits in higher-level perceptual processes, since there is evidence showing a reduced inversion effect for faces but not for cars in AD. To address the involvement of these higher processes, we investigated event-related potential (ERP) neural correlates of faces in a patient with AD showing a face recognition deficit. Eight healthy participants were tested as a control group. Participants performed different tasks following the stimulus presentation. In experiment 1, they should indicate whether the stimulus was either a face or a house or a scrambled image. In experiments 2 and 3, they should discriminate between upright and inverted faces (in experiment 2, stimuli were faces with neutral or fearful expressions, while in experiment 3, stimuli were famous or unfamiliar faces). Electrophysiological results reveal that the typical face-specific modulation of the N170 component, which is thought to reflect the structural encoding of faces, was not present in patient MCG, despite being affected by the emotional content of the face implicitly processed by MCG. Conversely, the N400 component, which is thought to reflect the recruitment of the memory trace of the face identity, was found to be implicitly modulated in MCG. These results may identify a possible role for gnosic processes in face recognition deficits in AD and suggest the importance of adopting an integrated approach to the AD diagnosis while considering electrophysiological markers

Event-related brain potentials in the study of inhibition: cognitive control, source localization and age-related modulations

In the previous 15 years, a variety of experimental paradigms and methods have been employed to study inhibition. In the current review, we analyze studies that have used the high temporal resolution of the event-related potential (ERP) technique to identify the temporal course of inhibition to understand the various processes that contribute to inhibition. ERP studies with a focus on normal aging are specifically analyzed because they contribute to a deeper understanding of inhibition. Three time windows are proposed to organize the ERP data collected using inhibition paradigms: the 200 ms period following stimulus onset; the period between 200 and 400 ms after stimulus onset; and the period between 400 and 800 ms after stimulus onset. In the first 200 ms, ERP inhibition research has primarily focused on N1 and P1 as the ERP components associated with inhibition. The inhibitory processing in the second time window has been associated with the N2 and P3 ERP components. Finally, in the third time window, inhibition has primarily been associated with the N400 and N450 ERP components. Source localization studies are analyzed to examine the association between the inhibition processes that are indexed by the ERP components and their functional brain areas. Inhibition can be organized in a complex functional structure that is not constrained to a specific time point but, rather, extends its activity through different time windows. This review characterizes inhibition as a set of processes rather than a unitary process

The physiologic correlates of learning in the classroom environment

This study served to further investigate learning and memory, and to offer a potential tool to support educational interventions. More specifically, this was accomplished by an investigation of the physiologic changes in the brain that occurred while students learned medical anatomy. A group of 29 students taking the Gross Anatomy course at Boston University School of Medicine participated in the study. Testing occurred in two sessions: prior to the course and at the completion of the course. For each session, scalp EEG was recorded while participants were shown 176 anatomical terms (132 relevant to the course and 44 obscure) and asked to respond with "Can Define", "Familiar", or "Don't Know". Behavioral results indicated a positive correlation between participants' course grades and performance on the experimental tasks. EEG results were analyzed for event-related potential (ERP) components related to two memory components: familiarity and recollection. Results had a number of indications. For Don't Know responses, a stronger early frontal, late parietal, and late frontal effect occurred more so for terms of Session 1 compared to Session 2. For an analysis of just Session 2 data, results indicated increased activity of the early frontal, late parietal, and late frontal effects for Can Define responses only. Session 2 Can Define responses elicited a stronger early frontal ERP, occurring between 300 and 500 milliseconds yet, the most post-retrieval processing and monitoring appeared for Can Define terms of Session 2. Ultimately, we focused on investigating two points: 1) the effect of classroom learning on memory, and 2) the examination of ERPs as a tool to guide education interventions. Specifically, ERPs would potentially indicate markers to predict whether students would retain materials long before behavioral measures indicate these results. This has potential to determine whether long-lasting or transient learning will occur; as well as the potential to support early intervention strategies for not just students, but also individuals with learning disabilities or memory impairments

Face blindness

Facial recognition is a complex task, often done immediately and readily, involving discrimination of subtle differences in facial structures with differences in facial expressions, ageing, perspectives and lighting. Facial recognition requires fast identification of stimuli which are then correlated against reservoirs of faces which are accumulated throughout life (Barton and Corrow, 2016). The facial recognition system is extremely complex, and if impaired, cannot be fully remedied by other areas of the brain. When such injury occurs early on in life, juvenile brain plasticity has been shown to be potentially inadequate to restore facial recognition functions, thereby suggesting that such an impairment can have severe, permanent implications, even at an early age (Barton et al., 2003) Damage to any part of the facial recognition mechanism may result in the development of face blindness. Such dysfunction results in the development of selective face-recognition and visual learning deficits, a condition called prosopagnosia. Prosopagnosia can be either acquired or congenital. The acquired form of prosopagnosia is considered to be a rare consequence of occipital or temporal lobe damage, possibly due to stroke or lesions occurring in adulthood. Congenital prosopagnosia, on the other hand, is usually not found associated with any gross abnormalities, and no clear underlying causative agent is found to be associated with the development of the disease (Grüter et al., 2008). Nevertheless, face blindness in children may also be associated with inherited or acquired brain lesions, and may not be exclusively of a congenital/hereditary aetiology. Moreover, prosopagnosia can also occur in association with other disorders, which may be psychiatric, developmental or associated with multiple types of visual impairment (Watson et al., 2016).peer-reviewe