Kartik K. Iyer

Scale-Free Bursting in Human Cortex following Hypoxia at Birth

The human brain is fragile in the face of oxygen deprivation. Even a brief interruption of metabolic supply at birth challenges an otherwise healthy neonatal cortex, leading to a cascade of homeostatic responses. During recovery from hypoxia, cortical activity exhibits a period of highly irregular electrical fluctuations known as burst suppression. Here we show that these bursts have fractal properties, with power-law scaling of burst sizes across a remarkable 5 orders of magnitude and a scale-free relationship between burst sizes and durations. Although burst waveforms vary greatly, their average shape converges to a simple form that is asymmetric at long time scales. Using a simple computational model, we argue that this asymmetry reflects activity-dependent changes in the excitatory–inhibitory balance of cortical neurons. Bursts become more symmetric following the resumption of normal activity, with a corresponding reorganization of burst scaling relationships. These findings place burst suppression in the broad class of scale-free physical processes termed crackling noise and suggest that the resumption of healthy activity reflects a fundamental reorganization in the relationship between neuronal activity and its underlying metabolic constraints.

Novel features of early burst suppression predict outcome after birth asphyxia

Burst suppression patterns in the electroencephalogram are a reliable marker of recent severe brain insult. Here we analyze statistical properties of bursts occurring in 20 electroencephalographic recordings acquired from hypothermic asphyxic newborns in the hours immediately following birth. We show that the distributions of burst area and duration in these acute data predict later clinical outcome in both structural neuroimaging and neurodevelopment. Our findings indicate the first early electroencephalographic metrics that offer outcome prediction in asphyxic neonates undergoing hypothermia treatment.

Critical role for resource constraints in neural models.

Criticality has emerged as a leading dynamical candidate for healthy and pathological neuronal activity. At the heart of criticality in neural systems is the need for parameters to be tuned to specific values or for the existence of self-organizing mechanisms. Existing models lack precise physiological descriptions for how the brain maintains its tuning near a critical point. In this paper we argue that a key ingredient missing from the field is a formulation of reciprocal coupling between neural activity and metabolic resources. We propose that the constraint of optimizing the balance between energy use and activity plays a major role in tuning brain states to lie near criticality. Important recent findings aligned with our viewpoint have emerged from analyses of disorders that involve severe metabolic disturbances and alter scale-free properties of brain dynamics, including burst suppression. Moreover, we argue that average shapes of neuronal avalanches are a signature of scale-free activity that offers sharper insights into underlying mechanisms than afforded by traditional analyses of avalanche statistics.

Early detection of preterm intraventricular hemorrhage from clinical electroencephalography

Objectives:Intraventricular hemorrhage is a common neurologic complication of extremely preterm birth and leads to lifelong neurodevelopmental disabilities. Early bedside detection of intraventricular hemorrhage is crucial to enabling timely interventions. We sought to detect early markers of brain activity that preempt the occurrence of intraventricular hemorrhage in extremely preterm infants during the first postnatal days. Design:Cross-sectional study. Setting:Level III neonatal ICU. Patients:Twenty-five extremely preterm infants (22–28 wk gestational age). Measurements and Main Results:We quantitatively assessed electroencephalography in the first 72 hours of postnatal life, focusing on the electrical burst activity of the preterm. Cranial ultrasound was performed on day 1 (0–24 hr) and day 3 (48–72 hr). Outcomes were categorized into three classes: 1) no intraventricular hemorrhage (grade 0); 2) mild-moderate intraventricular hemorrhage (grades 1–2, i.e., germinal matrix hemorrhages or intraventricular hemorrhage without ventricular dilatation, respectively); and 3) severe intraventricular hemorrhage (grades 3–4, i.e., intraventricular hemorrhage with ventricular dilatation or intraparenchymal involvement). Quantitative assessment of electroencephalography burst shapes was used to preempt the occurrence and severity of intraventricular hemorrhage as detected by ultrasound. The shapes of electroencephalography bursts found in the intraventricular hemorrhage infants were significantly sharper (F = 13.78; p < 0.0001) and less symmetric (F = 6.91; p < 0.015) than in preterm infants without intraventricular hemorrhage. Diagnostic discrimination of intraventricular hemorrhage infants using measures of burst symmetry and sharpness yielded high true-positive rates (82% and 88%, respectively) and low false-positive rates (19% and 8%). Conventional electroencephalography measures of interburst intervals and burst counts were not significantly associated with intraventricular hemorrhage. Conclusions:Detection of intraventricular hemorrhage during the first postnatal days is possible from bedside measures of brain activity prior to ultrasound confirmation of intraventricular hemorrhage. Significantly, our novel automated assessment of electroencephalography preempts the occurrence of intraventricular hemorrhage in the extremely preterm. Early bedside detection of intraventricular hemorrhage holds promise for advancing individual care, targeted therapeutic trials, and understanding mechanisms of brain injury in neonates.

Mechanisms of facial emotion recognition in autism spectrum disorders : Insights from eye tracking and electroencephalography

HIGHLIGHTSIndividuals with Autism Spectrum Disorder present with atypical gaze and cortical activation to facially expressed emotions.Individuals with Autism Spectrum Disorder may use compensatory strategies during facial emotion recognition.Individuals with Autism Spectrum Disorder may employ self‐regulatory strategies during facial emotion recognition.Eye tracking and electroencephalography findings may provide potential markers for diagnosis and treatment targets. ABSTRACT While behavioural difficulties in facial emotion recognition (FER) have been observed in individuals with Autism Spectrum Disorder (ASD), behavioural studies alone are not suited to elucidate the specific nature of FER challenges in ASD. Eye tracking (ET) and electroencephalography (EEG) provide insights in to the attentional and neurological correlates of performance, and may therefore provide insight in to the mechanisms underpinning FER in ASD. Given that these processes develop over the course of the developmental trajectory, there is a need to synthesise findings in regard to the developmental stages to determine how the maturation of these systems may impact FER in ASD. We conducted a systematic review of fifty‐four studies investigating ET or EEG meeting inclusion criteria. Findings indicate divergence of visual processing pathways in individuals with ASD. Altered function of the social brain in ASD impacts the processing of facial emotion across the developmental trajectory, resulting in observable differences in ET and EEG outcomes.

Pediatric Obstructive Sleep Apnea assessment using pulse oximetry and dual RIP bands

The diagnosis of Obstructive Sleep Apnea (OSA) in children presents a challenging diagnostic problem given the high prevalence (2–3%), the resource intensity of the overnight polysomnography investigation, and the realisation that OSA poses a serious threat to the healthy growth and development of children. Previous attempts to develop OSA diagnostic systems using home pulse oximetry studies have failed to meet the accuracy requirements - particularly the low false normal rate (FNR) - required for a pre-PSG screening test. Thus the aim of this study is to investigate the feasibility of an OSA severity diagnostic system based on both oximetry and dual respiratory inductance plethysmography (RIP) bands. A total of 90 PSG studies (30 each of normal, mild/moderate and severe OSA) were retrospectively analyzed. Quantifications of oxygen desaturations (S), respiratory events (E) and heart rate arousals (A) were calculated and extracted and an empirical rule-based SEA classifier model for normal, mild/moderate and severe OSA defined and developed. In addition, an automated classifier using a decision tree algorithm was trained and tested using a 10-fold cross-validation. The empirical classification system showed a correct classification rate (CCR) of 0.83 (Cohens Kappa κ=0.81, FNR=0.08), and the decision tree classifier achieved a CCR of 0.79 (κ=0.73, FNR=0.08) when compared to gold standard PSG assessment. The relatively high CCR, and low FNR indicate that a OSA severity system based on dual RIP and oximetry is feasible for application as a pre-PSG screening tool.

Non-linear changes to corticospinal excitability induced with increasing intensities of transcranial direct current stimulation

Non-invasive brain stimulation (NIBS) has become an extremely popular method of neuromodulation in both clinical and non-clinical populations. Of the NIBS techniques available, transcranial direct current stimulation (tDCS) has generated significant interest as it is both portable and inexpensive relative to transcranial magnetic stimulation (TMS). There are multiple tDCS parameters (e.g. stimulation intensity, duration, electrode size, etc.) that require optimisation to induce longer lasting and reproducible neuromodulation. In a recent study, Jamil et al. (2017) investigated changes in corticospinal excitability (CSE) up to 2 h following 15 min of tDCS with the anode (n = 20) or cathode (n = 18) electrode placed over the left primary motor cortex (M1) with a range of stimulation intensities (0.5–2 mA and sham). Changes in CSE were probed with single pulse TMS (25 trials each time point) at an intensity that induced 1 mV peak to peak motor evoked potentials (MEPs) at baseline. In addition, intra-individual variability in the response to 15 min of 1 mA tDCS with the anode over M1 was assessed over three separate sessions (sub-sample n = 7). Interestingly, increasing stimulation intensity resulted in non-linear changes in CSE for both tDCS polarities, such that low and high stimulation intensities had equivalent neuromodulatory effects on CSE. Compared to sham, all intensities delivered with the anode over M1 led to significant MEP facilitation, whereas in tDCS with the cathode over M1,

Effective assessments of electroencephalography during stroke recovery: contemporary approaches and considerations

Stroke is one of the leading causes of permanent disability worldwide, relying conventionally on extended periods of physiotherapy to recover functional ability. While neuroimaging techniques and emerging neurorehabilitation paradigms have advanced our understanding of pathophysiological mechanisms underlying stroke, recent evidence has renewed focus on quantifying features of cortical activity present in electroencephalography recordings to greatly enhance our understanding of stroke treatment and recovery. This Neuro Forum article reviews these key advances and discusses the importance of quantifying electroencephalography in future assessments of stroke survivors.

An EEG coherence-based analysis approach for investigating response conflict processes in 7 and 9-year old children

Understanding the development of the brains neural networks can reveal critical insights into the cognitive changes that occur from infancy to late childhood. Behavioural metrics including: task accuracy, stimuli recognition, and reaction time show dramatic changes over childhood. In this study we investigated response control using the Erikson Flanker task. In a dataset of 45 EEG recordings, we calculated spectral coherence to measure connectivity between all possible electrode pairs. Coherence measures were performed on two different trial conditions -congruent (where there is no response conflict) and incongruent (where response conflict is induced). The increase in incongruent coherence compared to the congruent was investigated for each electrode pair over 45 healthy subjects aged seven years. The same calculation was then performed on the same group of subjects two years later when they were aged nine years. The results revealed that at age seven years, increased coherence was detected in the left prefrontal to right and left parieto-occipital - i.e. an anatomical region located between the parietal and occipital lobes - within theta band. No increase was found for the older group-at age nine years- which may indicate cognitive development in conflict processing mechanism.

Modulating functional connectivity with non-invasive brain stimulation for the investigation and alleviation of age-associated declines in response inhibition: A narrative review

&NA; Response inhibition, the ability to withhold a dominant and prepotent response following a change in circumstance or sensory stimuli, declines with advancing age. While non‐invasive brain stimulation (NiBS) has shown promise in alleviating some cognitive and motor functions in healthy older individuals, NiBS research focusing on response inhibition has mostly been conducted on younger adults. These extant studies have primarily focused on modulating the activity of distinct neural regions known to be critical for response inhibition, including the right inferior frontal gyrus (rIFG) and the pre‐supplementary motor area (pre‐SMA). However, given that changes in structural and functional connectivity have been associated with healthy aging, this review proposes that NiBS protocols aimed at modulating the functional connectivity between the rIFG and pre‐SMA may be the most efficacious approach to investigate—and perhaps even alleviate—age‐related deficits in inhibitory control. HighlightsStructural and functional changes within the fronto‐basal‐ganglia network likely mediate declined inhibition in elderly.Non‐invasive brain stimulation can provide mechanistic insight into how executive functions deteriorate with advancing age.Non‐invasive brain stimulation modulating inter‐regional network activity may alleviate age‐related deficits in inhibition.