Andrew Papanicolaou

University of Tennessee at Knoxville | UTK · Department of Pediatrics

This review consists of three main sections. In the first, the Introduction, the main theories of the neuronal mediation of linguistic operations, derived mostly from studies of the effects of focal lesions on linguistic performance, are summarized. These models furnish the conceptual framework on which the design of subsequent functional neuroimag...

Introduction The single equivalent current dipole (sECD) is the standard clinical procedure for presurgical language mapping in epilepsy using magnetoencephalography (MEG). However, the sECD approach has not been widely used in clinical assessments, mainly because it requires subjective judgements in selecting several critical parameters. To addres...

Vivian Smith Advanced Summer Institute of the International Neuropsychological Society in Neuropsychology 20-year Reunion 2022

As is evident from the scientific chapters of this book, the technology of magnetoencephalography offers a combination of spatial, temporal, and spectral resolution, unique among neuroimaging technologies. While functional magnetic resonance imaging (fMRI) accommodates spatial resolution, it lacks the millisecond resolution (because of the reliance...

In the 50 years since magnetoencephalography (MEG) was invented, various clinical and research applications of it have been attempted with considerable success. This is most notable in the area of epilepsy and presurgical functioning mapping. However, the best ways to apply MEG and interpret the findings still remain conjectural. As such, this book...

The tendency of many neuroscientists, cognitive scientists, and psychologists to present, largely unwittingly, their metaphysical beliefs as scientifically established facts has been enhanced since the advent of noninvasive, functional brain imaging. In the second section of this chapter, titled “Word Salads,” I describe how this tendency is mediat...

Noninvasive functional brain imaging with magnetoencephalography (MEG) is regularly used to map the eloquent cortex associated with somatosensory, motor, auditory, visual, and language processing before a surgical resection to determine if the functional areas have been reorganized. Most tasks can also be performed in the pediatric population. To a...

Dynamic Functional Connectivity (DFC) analysis is a promising approach for the characterization of brain electrophysiological activity. In this study, we investigated abnormal alterations due to mild Traumatic Brain Injury (mTBI) using DFC of the source reconstructed magnetoencephalographic (MEG) resting-state recordings. Brain activity in several...

Intrinsic functional connectivity networks derived from different neuroimaging methods and connectivity estimators have revealed robust developmental trends linked to behavioural and cognitive maturation. The present study employed a dynamic functional connectivity approach to determine dominant intrinsic coupling modes in resting-state neuromagnet...

The inconsistency of volumetric results often seen in MR neuroimaging studies can be partially attributed to small sample sizes and variable data analysis approaches. Increased sample size through multi-scanner studies can tackle the former, but combining data across different scanner platforms and field-strengths may introduce a variability factor...

We demonstrated how dynamic functional connectivity analysis on source-reconstructed neuromagnetic activity can reveal characteristic brain states to mild traumatic brain injury (mTBI). The derived subject-specific symbolic time series that describe the transient behavior of brain states can feed the computation of trivial chronnectomics. Our study...

Objective: Self-monitoring is a crucial component of human empathy and necessary for the formation and repair of social relations. Several studies have brought to light possible neuronal substrates associated with self-monitoring, but the information that they have provided is inconclusive. The authors, therefore, studied a large group of patients...

Magnetoencephalography (MEG), which represents the most novel example of noninvasive functional mapping techniques, has contributed to the surgical management of epilepsy and brain tumors in two ways. First, in the case of epilepsy, MEG localization of interictal activity has facilitated placement of subdural (grid, strip, and depth) electrodes tha...

This chapter presents a summary of current notions regarding cortical specialization for language and a description of the methods employed for the assessment of that specialization. We distinguish between the "canonical" model of language specialization as it evolved from the early observations of Broca and Wernicke, implicating the inferior front...

Current study attempts to model the neuromagnetic resting-state recordings of mild Traumatic Brain Injury (mTBI) patients via the notion of time-resolved functional connectivity graphs. The activity of theta (θ) frequency band was first beamformed with linear constrained minimum norm variance in the artefact-free MEG data to determine ninety anatom...

Incidental memory can be defined as the ability to acquire information unintentionally. The present study investigated incidental memory performance in amnestic mild cognitive impairment (aMCI) and mild Alzheimer's disease (AD) patients; additionally, hippocampal atrophy between groupswas examined. Twenty-nine aMCI patients (14 with hippocampal atr...

Introduction: According to latest research, a percentage of cognitively impaired drivers fail to recognize their areas of weakness and overestimate their driving abilities. Methods: Twenty-seven individuals with amnestic mild cognitive impairment (MCI) and 26 healthy elderly drivers participated in a driving simulator study. After the driving as...

Neuroimaging studies have identified a variety of structural and functional connectivity abnormalities in students experiencing reading difficulties. The present study adopted a novel approach to assess the dynamics of resting-state neuromagnetic recordings in the form of symbolic sequences (i.e., repeated patterns of neuromagnetic fluctuations wit...

Neuroimaging studies have identified a variety of structural and functional connectivity abnormalities in students experiencing reading difficulties. The present study adopted a novel approach to assess the dynamics of resting-state neuromagnetic recordings in the form of symbolic sequences (i.e., repeated patterns of neuromagnetic fluctuations wit...

Neuroimaging studies have identified a variety of structural and functional connectivity abnormalities in students experiencing reading difficulties. The present study adopted a novel approach to assess the dynamics of resting-state neuromagnetic recordings in the form of symbolic sequences (i.e., repeated patterns of neuromagnetic fluctuations wit...

Driving is a multimodal task that requires the integrity of executive functions in order to process simultaneously multiple environmental cues, to predict the development of traffic situations, as well as to take rapid, accurate and safe decisions. Memory plays an important role, among others, on route planning and traffic signs recognition. In add...

In the present study a novel data-driven topological filtering technique is introduced to derive the backbone of functional brain networks relying on orthogonal minimal spanning trees (OMST). The method aims to identify the essential functional connections to ensure optimal information flow via the objective criterion of global efficiency minus the...

Considering the high incidence of depressive symptoms in Alzheimer’s disease (AD), we conducted a large-sample study to investigate the pattern of gray matter (GM) abnormalities that differentiates depressive from non-depressive AD patients. We included 201 AD patients who underwent MRI assessment and categorized them into depressive and non-depres...

In the present study a novel data-driven topological filtering technique is introduced to derive the backbone of functional brain networks relying on orthogonal minimal spanning trees (OMST). The method aims to identify the essential functional connections to ensure optimal information flow via the objective criterion of global efficiency minus the...

A number of investigators, starting with Benjamin Libet, tested the hypothesis that the human will is determined by antecedent neuronal events and sought to identify these antecedents. Reviewing the evidence for the existence of those events that cause the (putatively false) subjective impression of freedom of the will, one is forced to conclude th...

Functional brain connectivity networks exhibit “small-world” characteristics and some of these networks follow a “rich-club” organization, whereby a few nodes of high connectivity (hubs) tend to connect more densely among themselves than to nodes of lower connectivity. The Current study followed an “attack strategy” to compare the rich-club and sma...

The type of syntactic operations that increase neuronal activation in humans as a result of syntactically erroneous, unexpected lexical items in hearing sentences has remained unclear. In the present study, we used recordings of magnetoencephalographic (MEG) activity to compare bare infinitive and full infinitive constructions in English. This rese...

During the last few years, rich-club (RC) organization has been studied as a possible brain-connectivity organization model for large-scale brain networks. At the same time, empirical and simulated data of neurophysiological models have demonstrated the significant role of intra-frequency and inter-frequency coupling among distinct brain areas. The...

Cortical Stimulation Mapping (CSM) and the Wada procedure have long been considered the gold standard for localizing motor and language-related cortical areas and for determining the language and memory-dominant hemisphere, respectively. In recent years, however, non-invasive methods such as magnetoencephalography (MEG), functional magnetic resonan...

The results of this magnetoencephalography study challenge two long-standing assumptions regarding the brain mechanisms of language processing: First, that linguistic processing proper follows sensory feature processing effected by bilateral activation of the primary sensory cortices that lasts about 100 msec from stimulus onset. Second, that subse...

During the last few years, rich-club (RC) organization has been studied as a possible brain-connectivity organization model for large-scale brain networks. At the same time, empirical and simulated data of neurophysiological models have demonstrated the significant role of intra-frequency and inter-frequency coupling among distinct brain areas. The...

Though fairly well-studied in adults, less is known about the manifestation of resting state networks (RSN) in children. We examined the validity of RSN derived in an ethnically diverse group of typically developing 6- to 7-year-old children. We hypothesized that the RSNs in young children would be robust and would reliably show significant concord...

Objective: The aim of the current study was to investigate the impact of gender and age on incidental and intentional memory in healthy participants and to explore the strength of the association of incidental and intentional memory with attentional and executive functioning. Method: A total number of 47 participants underwent a driving simulati...

A series of studies that was initiated more than 30 years ago by Benjamin Libet (see Libet, Gleason, Wright, & Pearl, 1983) is thought to have furnished evidence that the felt freedom of the will is an illusion. Although this may very well be the case, it is the aim of this essay to show that the aforementioned studies do not support such a conclus...

Introduction The unique ability of TMS to non-invasively induce evoked responses and virtual lesions combined with improved accuracy afforded by image guidance has spurred its clinical applications. While the utility of presurgical motor and language mapping using TMS has been demonstrated in adults (Picht, 2013; Tarapore, 2012), its use in pediatr...

Ongoing fluctuations of neuronal activity have long been considered intrinsic noise that introduces unavoidable and unwanted variability into neuronal processing, which the brain eliminates by averaging across population activity (Georgopoulos et al., 1986; Lee et al., 1988; Shadlen and Newsome, 1994; Maynard et al., 1999). It is now understood, th...

Magnetoencephalography (MEG) is a brain imaging method affording real-time temporal, and adequate spatial resolution to reveal aberrant neurophysiological function associated with dyslexia. In this study we analyzed sensor-level resting-state neuromagnetic recordings from 25 reading-disabled children and 27 non-impaired readers under the notion of...

Diagnosis of mild Traumatic Brain Injury (mTBI) is difficult due to the variability of obvious brain lesions using imaging scans. A promising tool for exploring potential biomarkers for mTBI is magnetoencephalography which has the advantage of high spatial and temporal resolution. By adopting proper analytic tools from the field of symbolic dynamic...

Recent studies have investigated the possible role of dynamic functional connectivity and the role of cross-frequency coupling (CFC) to provide the substrate for reliable biomarkers of brain disorders. In this study, we analyzed time-varying CFC profiles from resting state Magnetoencephal-ographic recordings of 30 mild Traumatic Brain Injury (mTBI)...

Introduction: Self-estimation of performance implies the ability to understand one's own performance with relatively objective terms. Up to date, few studies have addressed this topic in mild cognitive impairment (MCI) patients. The aim of the present study was to compare objective measures of performance with subjective perception of specific per...

The aim of this study was to identify brain regions involved in motor imagery and differentiate two alternative strategies in its implementation: imagining a motor act using kinesthetic or visual imagery. Fourteen adults were precisely instructed and trained on how to imagine themselves or others perform a movement sequence, with the aim of promoti...

The brain generates oscillatory neuronal activity at a broad range of frequencies and the presence and amplitude of certain oscillations at specific times and in specific brain regions are highly correlated with states of arousal, sleep, and with a wide range of cognitive processes. The neuronal mechanisms underlying the generation of brain rhythms...

Cross-frequency, phase-to-amplitude coupling (PAC) between neuronal oscillations at rest may serve as the substrate that supports information exchange between functionally specialized neuronal populations both within and between cortical regions. The study utilizes novel algorithms to identify prominent instantaneous modes of cross-frequency coupli...

Objectives Characterize the scale and pattern of long-term atrophy in gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) in chronic moderate–severe traumatic brain injury (TBI) and its relationship to neurocognitive outcomes. Participants The TBI group consisted of 17 males with primary diagnosis of moderate–severe closed head inju...

The main clinical application of functional neuroimaging consists in mapping the brain areas that contain parts of the neuronal circuitry necessary for somatosensory, motor, and language functions and in assessing hemispheric dominance for language and for the encoding operations of memory prior to several types of brain surgery. Presently, functio...

The present data support the cross-language generalizability of a language protocol that was originally developed for patients with English as their primary language. The utility of such confirmatory studies lies in their ability to replicate prior studies as well as provide a novel contribution to understanding the brain mechanisms for cognitive...

Objective: The aim of the present study was to compare localization of the language cortex using cortical stimulation mapping (CSM), high gamma electrocorticography (hgECoG), functional magnetic resonance imaging (fMRI), and transcranial magnetic stimulation (TMS). Methods: Language mapping using CSM, hgECoG, fMRI, and TMS were compared in nine...

Mild traumatic brain injury (mTBI) may affect normal cognition and behavior by disrupting the functional connectivity networks that mediate efficient communication among brain regions. In this study, we analyzed brain connectivity profiles from resting state Magnetoencephalographic (MEG) recordings obtained from 31 mTBI patients and 55 normal contr...

Supplementary material.

By performing sensor-level analysis on magnetoencephalography (MEG) data we identified the dynamic evolution of the functional connectivity networks during a simple visuomotor task. The functional connectivity networks were constructed using the concept of phase-locking value (PLV). We illustrate that the task-related activity is mediated by distin...

Several neuroimaging studies have suggested that functional brain connectivity networks exhibit “small-world” characteristics, whereas recent studies based on structural data have proposed a “rich-club” organization of brain networks, whereby hubs of high connection density tend to connect among themselves compared to nodes of lower density. In thi...

In this study, we explored the relationship between physical activity, body composition and cortical function in a cohort of preschool children. All participants underwent resting magnetoencephalography (MEG), a non-invasive measure of direct neuronal activity, and estimates of physical activity and body composition were obtained using acceleromete...

The study of the brain mechanisms of mnemonic traces has recently been given substantial impetus by the development of various advanced techniques that can be used in humans and animals. The message of such studies is that the mnemonic traces or engrams of specific experiences are now being identified. This message, however, misrepresents what has...

In this study, we have addressed the question of functional brain reorganization for language in the presence and absence of anatomical lesions in two patients with epilepsy using cortical stimulation mapping and high gamma (HG) activity in subdural grid recordings. In both, the expressive language cortex was defined as the cortical patch below the...

Noninvasive brain stimulation is now an accepted technique that is used as a diagnostic aid and in the treatment of neuropsychiatric disorders in adults, and is being increasingly used in children. In this review, we will discuss the basic principles and safety of one noninvasive brain stimulation method, transcranial magnetic stimulation. Improvem...

The present study assessed the impact of sample size on the power and fit of struc-tural equation modeling applied to functional brain connectivity hypotheses. The data consisted of time-constrained minimum norm estimates of regional brain activity dur-ing performance of a reading task obtained with magnetoencephalography. Power analysis was first...

We formulate and analyze an inverse problem using derivatives prices to obtain a risk-neutral filtering density on volatility's hidden state. Stochastic volatility is the unobserved state in a hidden Markov model (HMM), and can be tracked using Bayesian filtering. However, derivative data can be considered as conditional expectations that are alrea...

Objective Accurate non-invasive assessment of motor function using functional MRI (fMRI) and magnetoencephalography (MEG) is a challenge in patients who are very young or who are developmentally delayed. In such cases, passive mapping of the sensorimotor cortex is performed under sedation. We examined the feasibility of using transcranial magnetic...

Non-invasive assessment of hemispheric dominance for receptive language using magnetoencephalography (MEG) is now a well-established procedure used across several epilepsy centers in the context of pre-surgical evaluation of children and adults while awake, alert and attentive. However, the utility of MEG for the same purpose, in cases of sedated p...