Effect of Enzogenol® Supplementation on Cognitive, Executive, and Vestibular/Balance Functioning in Chronic Phase of Concussion

This study examined the feasibility of Enzogenol® as a potential treatment modality for concussed individuals with residual symptoms in the chronic phase. Forty-two student-athletes with history of sport-related concussion were enrolled, comparing Enzogenol® versus placebo. Testing was conducted using virtual reality (VR) and electroencephalography (EEG), with neuropsychological (NP) tasks primarily used to induce cognitive challenges. After six weeks, the Enzogenol® group showed enhanced frontal-midline theta, and decreased parietal theta power, indicating reduced mental fatigue. Subjects enrolled in the Enzogenol® group also self-reported reduced mental fatigue and sleep problems. This suggests that Enzogenol® has the potential to improve brain functioning in the chronic phase of concussion.

Encoding of visual-spatial information in working memory requires more cerebral efforts than retrieval: Evidence from an EEG and virtual reality study

Visual-spatial working memory tasks can be decomposed into encoding and retrieval phases. It was hypothesized that encoding of visual-spatial information is cognitively more challenging than retrieval. This was tested by combining electroencephalography with a virtual reality paradigm to observe the modulation in EEG activity. EEG power analysis results demonstrated an increase in theta activity during encoding in comparison to retrieval, whereas alpha activity was significantly higher for retrieval in comparison to encoding. We found that encoding required more cerebral efforts than retrieval. Further, as seen in fMRI studies, we observed an encoding/retrieval flip in that encoding and retrieval differentially activated similar neural substrates. Results obtained from sLORETA identified cortical sources in the inferior frontal gyrus, which is a part of dorsolateral prefrontal cortex (DLPFC) during encoding, whereas the inferior parietal lobe and precuneus cortical sources were identified during retrieval. We further tie our results into studies examining the default network, which have shown increased activation in DLPFC occurs in response to increased cerebral challenge, while posterior parietal areas show activation during baseline or internal processing tasks. We conclude that encoding of visual-spatial information via VR navigation task is more cerebrally challenging than retrieval.

Are functional deficits in concussed individuals consistent with white matter structural alterations: combined FMRI & DTI study

There is still controversy in the literature whether a single episode of mild traumatic brain injury (MTBI) results in short-term functional and/or structural deficits as well as any induced long-term residual effects. With the inability of traditional structural brain imaging techniques to accurately diagnosis MTBI, there is hope that more advanced applications like functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) will be more specific in diagnosing MTBI. In this study, 15 subjects who have recently suffered from sport-related MTBI and 15 age-matched normal controls underwent both fMRI and DTI to investigate the possibility of traumatic axonal injury associated with functional deficits in recently concussed but asymptomatic individuals. There are several findings of interest. First, MTBI subjects had a more disperse brain activation pattern with additional increases in activity outside of the shared regions of interest (ROIs) as revealed by FMRI blood oxygen level-dependent (BOLD) signals. The MTBI group had additional activation in the left dorsal-lateral prefrontal cortex during encoding phase of spatial navigation working memory task that was not observed in normal controls. Second, neither whole-brain analysis nor ROI analysis showed significant alteration of white matter (WM) integrity in MTBI subjects as evidenced by fractional anisotropy FA (DTI) data. It should be noted, however, there was a larger variability of fractional anisotropy (FA) in the genu, and body of the corpus callosum in MTB subjects. Moreover, we observed decreased diffusivity as evidenced by apparent diffusion coefficient (ADC) at both left and right dorsolateral prefrontal cortex (DL-PFC) in MTBI subjects (P < 0.001). There was also a positive correlation (P < 0.05) between ADC and % change of fMRI BOLD signals at DL-PFC in MTBI subjects, but not in normal controls. Despite these differences we conclude that overall, no consistent findings across advanced brain imaging techniques (fMRI and DTI) were observed. Whether the lack of consistency across research techniques (fMRI & DTI) is due to time frame of scanning, unique nature of MTBI and/or technological issues involved in FA and Apparent Diffusion Coefficient (ADC) quantification is yet to be determined.

Alteration of cortical functional connectivity as a result of traumatic brain injury revealed by graph theory, ICA, and sLORETA analyses of EEG signals

In this paper, a novel approach to examine the cortical functional connectivity using multichannel electroencephalographic (EEG) signals is proposed. First we utilized independent component analysis (ICA) to transform multichannel EEG recordings into independent processes and then applied source reconstruction algorithm [i.e., standardize low resolution brain electromagnetic (sLORETA)] to identify the cortical regions of interest (ROIs). Second, we performed a graph theory analysis of the bipartite network composite of ROIs and independent processes to assess the connectivity between ROIs. We applied this proposed algorithm and compared the functional connectivity network properties under resting state condition using 29 student-athletes prior to and shortly after sport-related mild traumatic brain injury (MTBI). The major findings of interest are the following. There was 1) alterations in vertex degree at frontal and occipital regions in subjects suffering from MTBI, ( p < 0.05); 2) a significant decrease in the long-distance connectivity and significant increase in the short-distance connectivity as a result of MTBI, ( p < 0.05); 3) a departure from small-world network configuration in MTBI subjects. These major findings are discussed in relation to current debates regarding the brain functional connectivity within and between local and distal regions both in normal controls in pathological subjects.

Modulation of cortical activity as a result of task-specific practice

This report aims to examine the role of task-specific practice in the modification of finger force enslaving and to provide empirical evidence for specific EEG frequency bands accompanying such practice may be an end-effectors dependent phenomenon. Nine handed naïve subjects without any training in music participated in a pre- and post-practice sessions separated by 12 practice sessions. Subjects performed a series of isometric force production tasks at 10% and 50% maximum voluntary contraction (MVC) with two rates of force development separately by index and ring fingers. Task-specific practice aimed at suppressing the contribution of neighboring fingers was achieved via visual feedback of force traces. Behavioral data (accuracy of force production and amount of force enslaving) and EEG data in frequency domain obtained via Morlet Wavelet transforms were analyzed. The major behavioral finding is that task-specific practice significantly enhanced the accuracy of force production and individuated control of the "most enslaved" ring finger (P<0.01), but not the index finger. The major novel EEG findings are: (a) modulation of EEG activity within alpha band (8-12 Hz) in the central area of the brain as a function of practice was similar for both fingers and (b) after practice, modulation of EEG activity within gamma (30-50 Hz) band was end-effectors specific. Both behavioral and EEG patterns suggest an effect of task-specific practice on the reduction of force enslaving and that modulation of practice-related plasticity in the human cortex is end-effectors dependent phenomena.

Role of cerebral cortex in human postural control: an EEG study

OBJECTIVE

It was our primary objective to provide evidence supporting the existence of neural detectors for postural instability that could trigger the compensatory adjustments to avoid falls.

METHODS

Twelve young healthy subjects performed self-initiated oscillatory and discrete postural movements in the anterior-posterior (AP) directions with maximal range of motion predominantly at ankle joint. Movements were recorded by the system and included force plate and EMG, and EEG measures from 25 electrode sites. The center of pressure dynamics and stability index were calculated, and EEG potentials both in voltage and frequency domains were extracted by averaging and Morlet wavelet techniques, respectively.

RESULTS

The initiation of self-paced postural movement was preceded by slow negative DC shift, similar to movement-related cortical potentials (MRCP) accompanying voluntary limb movement. A burst of gamma activity preceded the initiation of compensatory backward postural movement when balance was in danger. This was evident for both oscillatory and discrete AP postural movements. The spatial distribution of EEG patterns in postural actions approximated that previously observed during the postural perceptual tasks.

CONCLUSIONS

The results suggest an important role of the higher cortical structures in regulation of posture equilibrium in dynamic stances. Postural reactions to prevent falls may be triggered by central command mechanisms identified by a burst of EEG gamma activity.

SIGNIFICANCE

The results from this study contribute to our understanding of neurophysiological mechanisms underlying the cortical control of human upright posture in normal subjects.

Modulation and experience of external stimuli: toward a science of experience and interoception

The concept of interoception can be found in various writing over the past 100 or more years dating back to Sherrington, James and Lange. Professor György Adám that made American scientists increasingly aware of the importance of interoception with his 1967 book Interoception and Behavior. In this article we want to discuss two areas of research from out laboratory that have been influenced from this perspective. First, we will focus on electrocortical correlates of error detection during visuo-motor task and examine the manner in which an individual becomes aware of making an error as well as the way in which this awareness directs behavior on an ongoing basis. Second, we will examine hypnotic modulation of the pain experience and describe the manner in which electrocortical processes reflect the modulation and experience of pain. In this discussion, we suggest the importance of the anterior cingulate in not only modulating these processes in particular but also in its more general role as an interface between the limbic system and the neocortex and the integration of cognitive with emotional stimuli.

Modulated cortical control of individual fingers in experienced musicians: an EEG study. Electroencephalographic study

OBJECTIVE

The present research was designed to address the nature of interdependency between fingers during force production tasks in subjects with varying experience in performing independent finger manipulation. Specifically, behavioral and electroencephalographic (EEG) measures associated with controllability of the most enslaved (ring) and the least enslaved (index) fingers was examined in musicians and non-musicians.

METHODS

Six piano players and 6 age-matched control subjects performed a series of isometric force production tasks with the index and ring fingers. Subjects produced 3 different force levels with either their index or ring fingers. We measured the isometric force output produced by all 4 fingers (index, ring, middle and little), including both ramp and static phases of force production. We applied time-domain averaging of EEG single trials in order to extract 4 components of the movement-related cortical potentials (MRCP) preceding and accompanying force responses.

RESULTS

Three behavioral findings were observed. First, musicians were more accurate than non-musicians at reaching the desired force level. Second, musicians showed less enslaving as compared to non-musicians. And third, the amount of enslaving increased with the increment of nominal force levels regardless of whether the index or ring finger was used as the master finger. In terms of EEG measures, we found differences between tasks performed with the index and ring fingers in non-musicians. For musicians, we found larger MRCP amplitudes at most electrode sites for the ring finger.

CONCLUSIONS

Our data extends previous enslaving research and suggest an important role for previous experience in terms of the independent use of the fingers. Given that a variety of previous work has shown finger independence to be reflected in cortical representation in the brain and our findings of MRCP amplitude associated with greater independence of fingers in musicians, this suggests that what has been considered to be stable constraints in terms of finger movements can be modulated by experience.

SIGNIFICANCE

This work supports the idea that experience is associated with changes in behavioral and EEG correlates of task performance and may have clinical implications in disorders such as stroke or focal hand dystonia. Practice-related procedures offer useful approaches to rehabilitation strategies.

The role of sub-maximal force production in the enslaving phenomenon

When individuals perform a force task involving only one finger, they involuntarily move other fingers as well. This phenomenon is referred to as the enslaving force or the interdependency of fingers. Given that previous literature on the enslaving force has focused on maximal isometric force production, the present research was designed to study the role of sub-maximal force production in the enslaving phenomenon. To this end, we examined behaviorally three levels of force production with a constant rate of force development. We also examined the temporal organization of enslaving separating the achievement of the desired force (ramp phase) and its maintenance (static phase). During the static phase we found: (i) the amount of enslaving increased with the increment of nominal force level whether the index, middle, ring or little fingers were used as the master finger; (ii) enslaving is strongest in the finger directly adjacent to the master finger; and (iii) in terms of enslaving, the index finger was more 'independent' than the other three fingers, regardless of nominal force produced, followed by the little, middle, and ring fingers. In terms of temporal organization, we found that the time-lag of activation of 'slave fingers' during the ramp phase was reduced as the amount of force level increased. Overall, our data suggest that enslaving effect is a task specific phenomenon and depends on the amount of force produced by the master finger.

Motor-related cortical potentials accompanying enslaving effect in single versus combination of fingers force production tasks

OBJECTIVES

This study examined behavioral indices and motor-related cortical potentials (MRCP) of the enslaving phenomenon (i.e. interdependency of finger movement) during isometric force production tasks using each of the four fingers separately and in combination. We examined MRCP preceding force production and those during the achievement of the desired force (ramp phase) and its maintenance (static phase).

METHODS

Our experimental design systematically controlled the isometric force output, including both ramp and static phases of force production. We applied time-domain averaging of electroencephalographic single trials in order to extract 3 components of MRCP (Bereitshaftspotential, motor potentials, and motor monitoring potentials) preceding and accompanying force responses.

RESULTS

We report two major findings. First, we found the index finger to be more independent, accurate, and to display the larger MRCP amplitude whereas the ring finger was more dependent, less accurate, and displayed smaller MRCP amplitude. Second, adding the neighboring finger when the ring finger produced the task significantly reduced its dependency on uninvolved fingers and increased the accuracy of both ramp and static phases which was not the case with the index finger. The amplitude of MRCP was increased when the ring finger produced the task in combination as compared to when the ring finger performed the task in isolation. In contrast, the amplitude of MRCP was significantly reduced when the index finger produced the task in combination with other fingers when compared to when the index finger performed the task in isolation.

CONCLUSIONS

Overall, the amount of the fingers' dependency on the uninvolved fingers (e.g. amount of enslaving) during isometric force production tasks was inversely related with the amplitude of MRCP indicating the contribution of central mechanisms to the enslaving phenomenon.

Movement-related EEG potentials are force or end-effector dependent: evidence from a multi-finger experiment

OBJECTIVES

This study examined behavioral and electrocortical responses in producing 3 levels of force (25, 50 and 75% of MVC) at a constant rate of force development with each of 4 fingers both during the achievement of the desired force (ramp phase) and its maintenance (static phase). We were particularly interested in describing in more detail the interaction between nominal force and finger on various components of movement-related potential (MRP) associated with preparation and execution of isometric force production tasks.

METHODS

Our experimental design systematically controlled the rate of force development while nominal force level was experimentally manipulated during isometric force production tasks. We applied time-domain averaging of EEG single trials in order to extract 3 components of MRP (BP(-600 to -500); MP(-100 to 0); MMP) preceding and accompanying behavioral responses.

RESULTS

Overall, as in our previous research the effect of force per se was not reflected in the EEG components. However, we did find an interaction between finger and force level in both the Bereitshaftspotential (BP) and motor potential (MP) components of the movement-related potentials. While the middle, ring and little finger produced no differences in EEG components at any of the 3 force levels, the index finger did. We further correlated the force trajectory and the EEG time series with the highest correlations found in the lowest force level with the index finger. As the force level was increased, the correlation was significantly reduced.

CONCLUSIONS

Overall, the whole complex of MRP components and evolution of EEG time series during multi-finger isometric force production tasks reflect a combination of factors including the primary end-effector performing the task and interaction of end-effector and the amount of nominal force.

Neurophysiological and behavioral concomitants of mild brain injury in collegiate athletes

OBJECTIVES

There is still limited understanding regarding the effect of mild brain injury (MBI) on normal functioning of the human brain with respect to motor control and coordination. To our knowledge, no research exists on how both the accuracy of force production and underlying neurophysiological concomitants are interactively affected by MBI. The aim of this study is to provide empirical evidence that there are at least transient functional changes in the brain associated with motor control and coordination in collegiate athletes suffering from MBI as reflected in alterations of force trajectory patterns and electroencephalogram (EEG) potentials both in time and frequency domains.

METHODS

Comparisons of the performance and concomitant EEG waveforms both in time and frequency domains of 6 collegiate athletes with MBI and 6 normal subjects in a series of isometric force production tasks were made. The traditional averaging techniques to obtain the slow-wave movement-related potentials (MRP) and Morlet wavelet transform to obtain EEG time-frequency (TF) profiles associated with task performance were used. Subjects performed isometric force production tasks when the level of nominal force was experimentally manipulated. EEG recordings from the frontal-central areas were analyzed with respect to the accuracy of force production during the ramp phase.

RESULTS

Behaviorally, the accuracy of force trajectory performance was considerably impaired in MBI subjects even when the amount of task force was only increased from 25 to 50% maximum voluntary contraction (MVC) within a given subject. Electro-cortically, impaired performance in MBI subjects was associated with alterations in EEG waveforms, amplitude of MRP and TF profiles of EEG.

CONCLUSIONS

Both behavioral and electro-cortical data of control subjects generally were comparable with those from subjects with MBI when small amounts of force were regulated. However, differences become apparent as the amount of task force production was increased. Overall our findings identify the presence of transient functional changes in the brain associated with motor control and coordination in subjects suffering from MBI.

Movement-related cortical potentials associated with progressive muscle fatigue in a grasping task

OBJECTIVE

The present research was aimed to further address the general empirical question regarding the behavioral and neurophysiological indices and mechanisms that contribute to and/or compensate for muscle fatigue. In particular, we examined isometric force production, EMG, and EEG correlates of progressive muscle fatigue while subjects performed a grasping task.

METHODS

Six neurologically healthy subjects were instructed to produce and maintain 70% of maximum voluntary contraction (MVC) for a total of 5 s in a sequence of 120 trials using a specially designed grip dynamometer. Three components of movement-related potentials (Bereitschaftspotential, BP, Motor potential, MP, and Movement-monitoring potential, MMP) were extracted from continuous EEG records and analyzed with reference to behavioral indicators of muscle fatigue.

RESULTS

Experimental manipulations induced muscle fatigue that was demonstrated by decreases in both MVC values and mean force levels produced concomitant to increases in EMG root mean square (RMS) amplitude with respect to baseline levels, and EMG slope. EEG data revealed a significant increase in MP amplitude at precentral (Cz and FCz) and contralateral (C3) electrode sites, and increases in BP amplitude at precentral (Cz and FCz) electrode sites.

CONCLUSIONS

The increases in EMG amplitude, EMG slope, and MP amplitudes suggest a possible link between the control signal originating in the motor cortex and activity level of the alpha-motoneuron pool as a function of progressive muscle fatigue. Overall, the data demonstrate that progressive muscle fatigue induced a systematic increase in the electrocortical activation over the supplementary motor and contralateral sensorimotor areas as reflected in the amplitude of movement-related EEG potentials.

Rate of force development and the lateralized readiness potential

We examined the relationship between force and rate of force development aspects of movement dynamics and electroencephalogram motor components as reflected in the lateralized readiness potential (LRP). Using self-paced tasks, in Studies 1 and 3 we investigated whether differential speed and accuracy constraints in discrete and repetitive finger force production tasks influenced the LRP. These studies showed that speed tasks produced larger LRP than accuracy tasks regardless of whether the movement type was discrete or repetitive. In Studies 2 and 4 we studied four conditions with two levels of force and two levels of rate of force development. The largest LRPs were found with the greatest rate of force development. Overall, the four studies demonstrated that preparation for differential rates of force development is a major component reflected in the LRP.

EEG correlates of finger movements as a function of range of motion and pre-loading conditions

OBJECTIVES

The present study was designed to obtain additional data regarding the differential influence of kinematic parameters and different nominal force levels upon components of movement-related cortical potentials (MRP) during index finger flexion.

METHODS

The absolute nominal force level of discrete movements was varied while the rate of force development remained constant within a given task. This was accomplished by utilizing a pre-loading experimental design at different ranges of index finger motion (25, 50 and 75 degrees), so that the movement kinematic profiles (velocity and acceleration) and rate of force development remained constant within each given range of motion. Time-domain averaging of EEG single trials was applied in order to extract 3 movement-related potentials (BP(-600 to -500), BP(-100 to 0) and N(0 to 100)) preceding and accompanying 25, 50 and 75 degrees of unilateral finger movement with no pre-load (0 g), small pre-load (100 g) and large pre-load (200 g).

RESULTS

The range of motion differentially influenced the amplitude of early (BP(-600 to -500)) and late (BP(-100 to 0)) MRP components spatially localized over frontal, central and parietal areas. The amplitude of the N(0 to 100) component localized over parietal and frontal areas was also sensitive toward experimental manipulations of the range of motion. Overall, the amplitude of N(0 to 100) localized over the central area was the only MRP component that was sensitive to the amount of pre-loading. However, within a given range of motion, none of the pre-loading conditions (0, 100 or 200 g) influenced the amplitude of MRP components.

CONCLUSIONS

The central finding was that an increase in nominal force production within a given range of motion did not influence MRP components when the rate of force development was held constant. It becomes especially apparent with strict control of kinematic and kinetic movement parameters that different methods of adding weight to the index finger performing the same movement patterns have different consequences for EEG correlates as reflected in the amplitude and spatial distribution of MRP. The range of motion of index finger flexion was the primary kinematic variable that consistently influenced MRP components both preceding and accompanying movement execution.

EEG correlates of wrist kinematics as revealed by averaging techniques and Morlet wavelet transforms

The question regarding the invariant movement properties the central nervous system may organize to accomplish different motor task demands as reflected in EEG remains unsolved. Surprisingly, no systematic electrocortical research in humans has related movement preparation with different movement distance, although this area has been widely investigated in the field of motor control. This study examined whether the amplitude of discrete wrist movements influences the various EEG components both in time and frequency domains. Time-domain averaging techniques and Morlet wavelet transforms of EEG single trials were applied in order to extract three components [BP(0), N1, and LPS] of movement related potentials (MRP) and to quantify changes in oscillatory activity of the movement-induced EEG waveforms accompanying 20, 40, and 60 unilateral wrist flexion movements. The experimental manipulations induced systematic changes in BP(0) and N1 amplitude along the midline (Fz, Cz, and Pz) with 20 movement showing the most negativity and 60 the least. The dominant energy within a 30-50 frequency cluster from bilateral precentral (C3, Cz, C4), frontal (F3, Fz, F4), and parietal (P3, Pz, P4) areas with maximum at vertex (Cz) also appeared to be sensitive to movement amplitude with the least power observed during 60 wrist flexion. This suggests that movement amplitude may be a controllable variable that is highly related with task-specific cortical activation primarily at frontocentral areas as reflected in EEG.

Human oscillatory brain activity within gamma band (30-50 Hz) induced by visual recognition of non-stable postures

Our principal finding from this study is that there were changes at the level of brain electrical activity (EEG) during cognitive tasks while subjects were instructed to visually recognize non-stable postures of a computer animated human body model. In particular, there was clear enhancement of the amplitude within the gamma band (30-50 Hz) activity associated with visual recognition of non-stable postures at fronto-central and parietal areas in all subjects. The Morlet's wavelet transform was applied to examine the change of time-frequency (TF) energy within a range of 1-70 Hz frequencies range as a function of experimental tasks. There was a high energy burst within the 35-45 Hz TF cluster at fronto-central and parietal areas when subjects visually recognized non-stable postures. Experimental evidences were provided demonstrating that EEG activity recorded during visual recognition of non-stable postures was related to specific judgement of postural instability. In a series of control experiments, additional evidences were provided to justify the specific sensitivity of EEG 40-Hz activity to the act of visual recognition of postural instability. The contamination of muscle activity in the reported EEG results during perceptual tasks was also ruled out. Our findings are consistent with the notion of existence of specialized neural detectors (predictors) for specific postures and goal-oriented behavior. However, the functional significance and precise cognitive and neurophysiological mechanisms predicting the existence of these detectors remain to be explored.

EEG correlates of finger movements with different inertial load conditions as revealed by averaging techniques

OBJECTIVE

The present study was aimed to further address the general empirical question regarding the sensitivity of EEG correlates toward specific kinematic and/or kinetic movement parameters. In particular, we examined whether adding different inertial loads to the index finger, while a subject produced various amplitudes of discrete finger movements, influenced the movement-related potentials (MRP).

METHODS

Our experimental design systematically controlled the angular displacement, velocity and acceleration (kinematic) profiles of finger movement while torque (kinetics) was varied by adding different external loads opposing finger flexion movement. We applied time-domain averaging of EEG single trials in order to extract three movement-related potentials (BP-600 to -500 BP-100 to 0 and N0 to 100) preceding and accompanying 25, 50 and 75 degrees unilateral finger movements with no inertial load, small (100 g) and large (200 g) loading.

RESULTS

It was shown that both inertial load and the degree of angular displacement of index finger flexion increased the amplitude of late components of MRP (BP-100 to 0 and N0 to 100) over frontal and precentral areas. In contrast, the external load and movement amplitude manipulations did not influence the earlier component of the MRP (BP- 600 to -500).

CONCLUSIONS

Overall, the data demonstrate that adding inertial load to the finger with larger angular displacements involves systematic increase in activation across frontal and precentral areas that are related to movement initiation as reflected in BP-100 to 0 and N0 to 100.