A multimodal brain-based feedback and communication system

The Thought Translation Device (TTD) is a brain-computer interface based on the self-regulation of slow cortical potentials (SCPs) and enables completely paralyzed patients to communicate using their brain potentials. Here, an extended version of the TTD is presented that has an auditory and a combined visual and auditory feedback modality added to the standard visual feedback. This feature is necessary for locked-in patients who are no longer able to focus their gaze. In order to test performance of physiological regulation with auditory feedback 54 healthy participants were randomly assigned to visual, auditory or combined visual-auditory feedback of slow cortical potentials. The training consisted of three sessions with 500 trials per session with random assignment of required cortical positivity or negativity in half of the trials. The data show that physiological regulation of SCPs can be learned with auditory and combined auditory and visual feedback although the performance of auditory feedback alone was significantly worse than with visual feedback alone.This study was supported by the Deutsche Forschungsgemeinschaft (DFG) SFB 550/B5, and the National Institute of Health (NIH)     

Synchronous unit activity and local field potentials evoked in the subthalamic nucleus by cortical stimulation

The responses of single subthalamic nucleus (STN) neurons to cortical activation are complex and depend on the relative activation of several neuronal circuits, making theoretical extrapolation of single neuron responses to the population level difficult. To understand better the degree of synchrony imposed on STN neurons and associated neuronal networks by cortical activation, we recorded the responses of single units, pairs of neighboring neurons, and local field potentials (LFPs) in STN to discrete electrical stimulation of the cortex in anesthetized rats. Stimulation of ipsilateral frontal cortex, but not temporal cortex, generated synchronized "multiphasic" responses in neighboring units in rostral STN, usually consisting of a brief, short-latency excitation, a brief inhibition, a second excitation, and a long-duration inhibition. Evoked LFPs in STN consistently mirrored unit responses; brief, negative deflections in the LFP coincided with excitations and brief, positive deflections with inhibitions. This characteristic LFP was dissimilar to potentials evoked in cortex and structures surrounding STN and was resistant to fluctuations in forebrain activity. The short-latency excitation and associated LFP deflection exhibited the highest fidelity to low-intensity cortical stimuli. Unit response failures, which mostly occurred in caudal STN, were not associated with LFPs typical of rostral STN. These data suggest that local populations of STN neurons can be synchronized by both direct and indirect cortical inputs. Synchronized ensemble activity is dependent on topography and input intensity. Finally, the stereotypical, multiphasic profile of the evoked LFP indicates that it might be useful for locating the STN in clinical as well as nonclinical settings.     

Increased cognitive load during simple and complex motor tasks in acute stage after stroke.

The aim of this study was to assess the activation of primary motor cortex, prefrontal cortex and parietal cortex during simple and complex motor tasks performed with the hemiparetic and non-hemiparetic hand. METHODS: Seven patients after stroke in the left brain hemisphere were included in the study. Functional magnetic resonance imaging (fMRI) was performed in the first and third week, and in three patients also three months after the stroke. RESULTS: Performance of both the simple and the complex tasks with the hemiparetic or non-hemiparetic hand resulted in activations of the motor cortex, prefrontal cortex and parietal cortex in majority of the consecutive fMRI sessions. Three months after the stroke fMRI data revealed reduced activation of primary motor cortex and parietal cortex in the contralesional hemisphere during the performance of the simple task by the hemiparetic hand. During the complex task, the reduction of activation was less prominent. CONCLUSIONS: Results of the present study suggest that in mildly impaired stroke patients a bilateral activation of prefrontal and parietal cortex may participate in the recovery process from stroke. The potential for measurement of cortical rehabilitation is discussed.     

Distinguishable brain activation networks for short- and long-term motor skill learning

The acquisition of a new motor skill is characterized first by a short-term, fast learning stage in which performance improves rapidly, and subsequently by a long-term, slower learning stage in which additional performance gains are incremental. Previous functional imaging studies have suggested that distinct brain networks mediate these two stages of learning, but direct comparisons using the same task have not been performed. Here we used a task in which subjects learn to track a continuous 8-s sequence demanding variable isometric force development between the fingers and thumb of the dominant, right hand. Learning-associated changes in brain activation were characterized using functional MRI (fMRI) during short-term learning of a novel sequence, during short-term learning after prior, brief exposure to the sequence, and over long-term (3 wk) training in the task. Short-term learning was associated with decreases in activity in the dorsolateral prefrontal, anterior cingulate, posterior parietal, primary motor, and cerebellar cortex, and with increased activation in the right cerebellar dentate nucleus, the left putamen, and left thalamus. Prefrontal, parietal, and cerebellar cortical changes were not apparent with short-term learning after prior exposure to the sequence. With long-term learning, increases in activity were found in the left primary somatosensory and motor cortex and in the right putamen. Our observations extend previous work suggesting that distinguishable networks are recruited during the different phases of motor learning. While short-term motor skill learning seems associated primarily with activation in a cortical network specific for the learned movements, long-term learning involves increased activation of a bihemispheric cortical-subcortical network in a pattern suggesting "plastic" development of new representations for both motor output and somatosensory afferent information.     

Primary visual cortex and memory

The purpose of this study was to identify the functional fields activated in relation to gestural movements. Using functional magnetic resonance imaging (fMRI), we mapped brain activity in ten right-handed, normal volunteers during activation and control tasks. The activation condition consisted of pantomiming tool-use gestures with either the left hand or right hand, whereas the control condition comprised repetitive, oppositional movements between thumb and index finger. Activated cortical regions were highly lateralized to the left hemisphere during pantomiming of tool use regardless of hand used. Praxis with either hand commonly activated the superior parietal lobule, supplementary motor area, premotor area of the left hemisphere, and cerebellar vermis. However, minimal activation occurred in the inferior parietal lobule, which has been known to be a critical area for praxis generation. Compared with left-hand praxis, right-hand praxis exhibited additional activation in the left putamen and posterior part of the left inferior temporal region. Our findings concur with neuropsychological observations that the left hemisphere in right-handers mediates programming and executing skilled movements and that, within the left hemisphere, praxis is predominantly subserved by the parietal lobe, supplementary motor area, and premotor area. However, unlike previous lesion studies, the results of our fMRI study suggested that the superior parietal lobule more likely than the inferior parietal lobule play an important role in gesture production. Electronic Publication     

Sex-related differences in the hemispheric laterality of slow cortical potentials during the preparation of visually guided movements

Previous work suggests the presence of sex differences in the laterality of brain activity in the premotor–parietal network during the preparation of visually guided reaching movements. In the current study, electroencephalography was used to test the hypothesis that women would have higher amplitude potentials over frontal and parietal regions ipsilateral to arm movements, relative to men. Event-related slow cortical potentials (SCPs) were collected from 30 participants (15 men and 15 women) during the performance of two visually guided reaching conditions (eyes and arm moved to the same spatial location or moved in opposite directions). The results of the study demonstrate that the amplitudes of SCPs were significantly higher overlying frontal regions of the right hemisphere of women relative to men. These differences were present both during an instructed-delay period prior to receiving a go-signal to initiate movement and during the period just prior to movement initiation. The study also revealed an interaction of Sex and Condition in the parietal region during the pre-movement period. These results suggest that motor preparatory activity in men mainly occurs in the hemisphere contralateral to reaching but that preparatory activity in women is distributed relatively more bilaterally. However, the nature of these differences changes over the time course of the preparatory period and is partially dependent on the type of visuomotor mapping being performed.     

Erratum to: Sex-related differences in the hemispheric laterality of slow cortical potentials during the preparation of visually guided movements

Previous work suggests the presence of sex differences in the laterality of brain activity in the premotor–parietal network during the preparation of visually guided reaching movements. In the current study, electroencephalography was used to test the hypothesis that women would have higher amplitude potentials over frontal and parietal regions ipsilateral to arm movements, relative to men. Event-related slow cortical potentials (SCPs) were collected from 30 participants (15 men and 15 women) during the performance of two visually guided reaching conditions (eyes and arm moved to the same spatial location or moved in opposite directions). The results of the study demonstrate that the amplitudes of SCPs were significantly higher overlying frontal regions of the right hemisphere of women relative to men. These differences were present both during an instructed-delay period prior to receiving a go-signal to initiate movement and during the period just prior to movement initiation. The study also revealed an interaction of Sex and Condition in the parietal region during the pre-movement period. These results suggest that motor preparatory activity in men mainly occurs in the hemisphere contralateral to reaching but that preparatory activity in women is distributed relatively more bilaterally. However, the nature of these differences changes over the time course of the preparatory period and is partially dependent on the type of visuomotor mapping being performed.     

Simultaneous recording of slow brain potentials and transcranial magnetic stimulation of hand area in human motor cortex

Recording of slow brain potentials (SPs) and transcranial magnetic stimulation (TCMS) of the human motor cortex were combined to probe the relationship between SP level and excitability of cortical neurons. In experiment 1, TCMS was applied during and shortly after the warning interval in a forewarned reaction time task. Electromyographic (EMG) responses to TCMS increased only slightly during the warning interval and were significantly elevated 150 ms after the imperative stimulus. In experiment 2, TCMS was applied during biofeedback-induced cortical positivity and negativity. In this non-motor task a dependence of TCMS response on SP amplitude was not significant. Results indicate higher local excitability of motor cortex during cortical negativity when a preparatory motor task in required. TCMS may better be suited to probe processes involved in motor tasks rather than non-motor and cognitive conditions.     

The Effects of Slow Cortical Potentials on Response Speed

The relationship between slow cortical potentials (SCPs) and response speed was investigated by training subjects to induce different cortical shifts by means of a biofeedback procedure. During two identical experimental sessions trials with visual feedback of the actual DC-shifts alternated with reaction time trials without feedback. In reaction time trials only the signal for the required change in polarity was provided. At the end of the signal interval an immediate button-press was required to stop a hissing noise. Two groups of 10 subjects each were investigated, one group receiving feed back from the left precentral recording(C₃) and the other from the right precentral recording (C₄). Results showed that subjects achieved control over their SCPs. At the end of the training period in the second session significant differences in SCPs between trials of the different required polarities were observed, during feedback trials as well as during reaction time trials without feedback. Subjects responded faster during trials in which a change toward more cortical negativity was required as compared to trials requiring less negativity.     

Self-Report During Feedback Regulation of Slow Cortical Potentials

Subjects received exteroceptive feedback for bidirectional changes in slow cortical potentials or alpha power measured from the vertex. The slow potential group succeeded in shifting slow potentials toward negativity and positivity on feedback and transfer trials requiring these changes, after two sessions of training. Differentiation of negativity and positivity was accompanied by verbal reports of somatomotor activation that occurred on trials on which negative slow potentials were required (p less than .01). Vertical and lateral eye movements, chin and frontalis electromyogram, and heart rate did not differentiate between negativity and positivity trials in the slow potential negativity during feedback. Although the alpha power group did not succeed at controlling changes in alpha, evidence of a training effect appeared in verbal reports of emotional arousal (p less than .05) and focused vision (p less than .08) on alpha suppression trials in this group. We discuss the findings from the viewpoint that biofeedback tasks involving electrocortical responses are problems in the organization of action that subjects seek to solve.     

Neural basis for the processes that underlie visually guided and internally guided force control in humans

Despite an intricate understanding of the neural mechanisms underlying visual and motor systems, it is not completely understood in which brain regions humans transfer visual information into motor commands. Furthermore, in the absence of visual information, the retrieval process for motor memory information remains unclear. We report an investigation where visuomotor and motor memory processes were separated from only visual and only motor activation. Subjects produced precision grip force during a functional MRI (fMRI) study that included four conditions: rest, grip force with visual feedback, grip force without visual feedback, and visual feedback only. Statistical and subtractive logic analyses segregated the functional process maps. There were three important observations. First, along with the well-established parietal and premotor cortical network, the anterior prefrontal cortex, putamen, ventral thalamus, lateral cerebellum, intermediate cerebellum, and the dentate nucleus were directly involved in the visuomotor transformation process. This activation occurred despite controlling for the visual input and motor output. Second, a detailed topographic orientation of visuomotor to motor/sensory activity was mapped for the premotor cortex, parietal cortex, and the cerebellum. Third, the retrieval of motor memory information was isolated in the dorsolateral prefrontal cortex, ventral prefrontal cortex, and anterior cingulate. The motor memory process did not extend to the supplementary motor area (SMA) and the basal ganglia. These findings provide evidence in humans for a model where a distributed network extends over cortical and subcortical regions to control the visuomotor transformation process used during visually guided tasks. In contrast, a localized network in the prefrontal cortex retrieves force output from memory during internally guided actions.     

Emotional perception: Correspondence of early and late event-related potentials with cortical and subcortical functional MRI

This research examines the relationship between brain activity recorded with functional magnetic resonance imaging (fMRI) and event related potentials (ERP) as these responses varied over a series of emotionally evocative and neutral pictures. We investigate the relationship of early occipitotemporal and later centroparietal emotion-modulated ERPs in one sample to fMRI estimates of neural activity in another sample in a replicated experiment. Using this approach, we aimed to link effects found in time-resolved electrocortical measures to specific neural structures across individual emotional and nonemotional picture stimuli. The centroparietal late positive potential (LPP) showed covariation with emotion-modulated regions of hemodynamic activation across multiple dorsal and ventral visual cortical structures, while the early occipitotemporal potential was not reliably associated. Subcortical and corticolimbic structures involved in the perception of motivationally relevant stimuli also related to modulation of the LPP, and were modestly associated to the amplitude of the early occipitotemporal potential. These data suggest that early occipitotemporal potentials may reflect multiple sources of modulation including motivational relevance, and supports the perspective that the slow-wave LPP represents aggregate cortical and subcortical structures involved in emotional discrimination.     

Local field potentials allow accurate decoding of muscle activity

Local field potentials (LFPs) in primary motor cortex include significant information about reach target location and upper limb movement kinematics. Some evidence suggests that they may be a more robust, longer-lasting signal than action potentials (spikes). Here we assess whether LFPs can also be used to decode upper limb muscle activity, a complex movement-related signal. We record electromyograms from both proximal and distal upper limb muscles from monkeys performing a variety of reach-to-grasp and isometric wrist force tasks. We show that LFPs can be used to decode activity from both proximal and distal muscles with performance rivaling that of spikes. Thus, motor cortical LFPs include information about more aspects of movement than has been previously demonstrated. This provides further evidence suggesting that LFPs could provide a highly informative, long-lasting signal source for neural prostheses.     

Evoked potentials in motor cortical local field potentials reflect task timing and behavioral performance

Evoked potentials (EPs) are observed in motor cortical local field potentials (LFPs) during movement execution (movement-related potentials [MRPs]) and in response to relevant visual cues (visual evoked potentials [VEPs]). Motor cortical EPs may be directionally selective, but little is known concerning their relation to other aspects of motor behavior, such as task timing and performance. We recorded LFPs in motor cortex of two monkeys during performance of a precued arm-reaching task. A time cue at the start of each trial signaled delay duration and thereby the pace of the task and the available time for movement preparation. VEPs and MRPs were strongly modulated by the delay duration, VEPs being systematically larger in short-delay trials and MRPs larger in long-delay trials. Despite these systematic modulations related to the task timing, directional selectivity was similar in short and long trials. The behavioral reaction time was positively correlated with MRP size and negatively correlated with VEP size, within sessions. In addition, the behavioral performance improved across sessions, in parallel with a slow decrease in the size of VEPs and MRPs. Our results clearly show the strong influence of the behavioral context and performance on motor cortical population activity during movement preparation and execution.     

Primary motor cortex activation by transcranial direct current stimulation in the human brain

Transcranial direct current stimulation (tDCS) can modulate motor cortex excitability in the human brain. We attempted to demonstrate the cortical stimulation effect of tDCS on the primary motor cortex (M1) using functional MRI (fMRI). An fMRI study was performed for 11 right-handed healthy subjects at 1.5 T. Anodal tDCS was applied to the scalp over the central knob of the M1 in the left hemisphere. A constant current with an intensity of 1.0 mA was applied. The total fMRI paradigm consisted of three sessions with a 5-min resting period between each session. Each session consisted of five successive phases (resting-tDCS-tDCS-tDCS-tDCS), and each of the phases was performed for 21s. Our findings revealed that no cortical activation was detected in any of the stimulation phases except the fourth tDCS phase. In the result of group analysis for the fourth tDCS phase, the average map indicated that the central knob of the left primary motor cortex was activated. In addition, there were activations on the left supplementary motor cortex and the right posterior parietal cortex. We demonstrated that tDCS has a direct stimulation effect on the underlying cortex. It seems that tDCS is a useful modality for stimulating a target cortical region.     

Operant conditioning of left-hemispheric slow cortical potentials and its effect on word processing

This study investigated whether language-related cognitive processes can be modified by learned modulation of cortical activity. Study participants received feedback of slow cortical potentials (SCPs) recorded above left-hemispheric language cortices and were reinforced for producing negative and positive shifts upon two different discriminative stimuli. In all subjects who achieved reliable control of left-hemispheric brain responses, substantial modification of word processing was observed. Behavioral modification could be documented in two experiments in which word probes were presented following discriminative stimuli. When negative shifts of the EEG were required, lexical decisions on words were substantially speeded, while they were slowed during positivity conditions. There was no indication for any performance difference between conditions in control subjects who failed to achieve control over SCPs after feedback training. This result was replicated in an experiment using lateralized-tachistoscopic stimulus presentation. Comparisons of word and pseudoword responses in both experiments indicated that behavioral modification was most pronounced for word responses. It was also not seen in a simple reaction time task not involving language materials. This argues against a global effect related to perception, visuo-spatial attention, or motor processes. We conclude that linguistic processes can be influenced by modification of cortical activity due to operant conditioning. In closing, tentative explanations of the present results based on theories of language and attention processes are being discussed.     

Projection from the thalamic intralaminar nuclei on the isocortex of the rat: a surface potential study

Summary Cortical surface potentials evoked from thalamic intralaminar nuclei have been studied in rats anaesthetized with chloralose. Stimulation with low current intensity in central lateral nucleus (CL), evoked potentials in large areas of the rat isocortex. In the posterior parietal cortex responses with a short latency negativity were evoked which followed high frequency repetitive stimulation. Its latency and ability to follow high frequency stimulation indicated a monosynaptic connection from CL to this part of the cortex. The short latency potential was followed by a second negativity with longer latency and varying amplitude. This second negativity did not follow repetitive stimulation exceeding 10 Hz, and was also reduced by supplementary doses of anaesthetics, indicating a polysynaptic origin. Stimulation at different CL sites elicited cortical potentials with short latency in a topographical pattern. Laminar analysis in the parietal and motor cortex suggested both a superficial and a deep layer termination of afferents from CL. Similar topografical relations and afferent layer distributions have previously been found in cats. The role of the thalamocortical projection from CL to parietal cortex in arousal, attention and pain mechanisms is discussed.     

Relationship between muscle output and functional MRI-measured brain activation

The relationship between functional MRI (fMRI)-measured brain signal and muscle force and or electromyogram (EMG) is critical in interpreting fMRI data and understanding the control mechanisms of voluntary motor actions. We designed a system that could record joint force and surface EMG online with fMRI data. High-quality force and EMG data were obtained while maintaining the quality of the fMRI brain images. Using this system, we determined the relationship between fMRI-measured brain activation and handgrip force and between fMRI-measured brain signal and EMG of extrinsic finger muscles. Ten volunteers participated in the experiments (only seven subjects' data were analyzed due to excessive noise in the fMRI data of three subjects). The participants exerted 20%, 35%, 50%, 65%, and 80% of the maximal force. During each contraction period, handgrip force, surface EMG of the finger flexor and extensor muscles, and fMRI brain images were acquired. The degree of muscle activation (force and EMG) was directly proportional to the amplitude of the brain signal determined by fMRI in the entire brain and in a number of motor function-related cortical fields, including primary motor, sensory regions, supplementary motor area, premotor, prefrontal, parietal and cingulate cortices, and cerebellum. All the examined brain areas demonstrated a similar relationship between the fMRI signal and force. A stronger fMRI signal during higher force indicates that more cortical output neurons and/or interneurons may participate in generating descending commands and/or processing additional sensory information. The similarity in the relationship between muscle output and fMRI signal in the cortical regions suggests that correlated or networked activation among a number of cortical fields may be necessary for controlling precise static force of finger muscles. Electronic Publication     

When a child errs: The ERN and the Pe complex in children

We report an analysis of the componential structure of the event‐related potentials (ERPs) elicited when 8–10‐year‐old children err. We demonstrated previously that the positive deflection that follows the error‐related negativity (ERN) in young adults is a combination of two ERP components, a fronto‐central positive component and a P300. As these findings affect the interpretation of error‐related ERP data, it is essential to determine if the componential structure of the ERPs elicited by children's errors is similar to that found in young adults. The results of the current study confirm that, as is the case in adults, both an ERN and a fronto‐central positivity are elicited by errors committed by children. In contrast to what has been previously found in adults, errors committed by children elicited a central positivity in addition to a parietal negativity that was elicited by correct responses.     

EEG Correlates of Action Observation in Humans

To investigate electrophysiological correlates of action observation electroencephalogram (EEG) was recorded while participants observed repetitive biological (human) or non-biological movements (at a rate of 2 Hz). Steady-state evoked potentials were analyzed and their neural sources were investigated using low resolution electromagnetic tomography analysis (LORETA). Results revealed significantly higher activation in the primary motor and premotor cortex, supplementary motor area as well as the posterior parietal cortices during observation of biological movements, supporting mirror properties of cortical motor neurons. In addition interregional communication was analyzed. Increased coherence for distributed networks at delta (0.5–4 Hz) and lower alpha (8–10 Hz) frequencies were obtained suggesting integration and functional coupling between the activated cortical regions during human action observation.