Biology subjects

Richardson, R. M.

Publications and source records attributed to Richardson, R. M..

27 records · Page 2Linked to original sources

bioRxiv2019

Shrinkage Classification for Overlapping Time Series: An interpretable method for mapping stimulus-differentiated evoked response

Multivariate time series from neural electrophysiological recordings are a rich source of information about neural processing systems and require appropriate methods for proper analysis. Current methods for mapping brain function in these data using neural decoding aggregate information across space and time in limited ways, rarely incorporating spatial dependence across recording locations. We propose Shrinkage Classification for Overlapping Time Series (SCOTS), a neural decoding method that maps brain function, while accounting for spatio-temporal dependence, through interpretable dimensionality reduction and classification of multivariate neural time series. SCOTS has two components: first, overlapping clustering from sparse semi-nonnegative matrix factorization gives a data-driven aggregation of neural information across space; second, wavelet-transformed nearest shrunken centroids with sparse group lasso performs multi-class classification with selection of informative clusters and time intervals. We demonstrate use of SCOTS by applying it to human intracranial electrophysiological and MEG data collected while participants viewed visual stimuli from a range of categories. The method reveals the dynamic activation of brain regions with sensitivity to different object categories, giving insight into spatio-temporal contributions of these neural processing systems.

neuroscience↗

bioRxiv2019

Differential Tractography as a Track-Based Biomarker for Neurodegeneration

Diffusion MRI tractography has been used to map the axonal structure of human brain, but its ability to detect neuronal injury is yet to be explored. Here we report differential tractography, a new type of tractography that utilizes repeat MRI scans and a novel tracking strategy to map the exact segment of fiber pathways with a neuronal injury. We examined differential tractography on multiple sclerosis, Huntington disease, amyotrophic lateral sclerosis, and epileptic patients. The results showed that the affected pathways shown by differential tractography matched well with the unique clinical symptoms of the patients, and the false discovery rate of the findings could be estimated using a sham setting to provide a reliability measurement. This novel approach enables a quantitative and objective method to monitor neuronal injury in individuals, allowing for diagnostic and prognostic evaluation of brain diseases.

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bioRxiv2018

Subthalamic nucleus and sensorimotor cortex activity during speech production

The sensorimotor cortex is somatotopically organized to represent the vocal tract articulators, such as lips, tongue, larynx, and jaw. How speech and articulatory features are encoded at the subcortical level, however, remains largely unknown. We analyzed local field potential (LFP) recordings from the subthalamic nucleus (STN) and simultaneous electrocorticography recordings from the sensorimotor cortex of 11 patients (1 female) with Parkinsons disease during implantation of deep brain stimulation (DBS) electrodes, while patients read aloud three-phoneme words. The initial phonemes involved either articulation primarily with the tongue (coronal consonants) or the lips (labial consonants). We observed significant increases in high gamma (60-150 Hz) power in both the STN and the sensorimotor cortex that began before speech onset and persisted for the duration of speech articulation. As expected from previous reports, in the sensorimotor cortex, the primary articulator involved in the production of the initial consonant was topographically represented by high gamma activity. We found that STN high gamma activity also demonstrated specificity for the primary articulator, although no clear topography was observed. In general, subthalamic high gamma activity varied along the ventral-dorsal trajectory of the electrodes, with greater high gamma power recorded in the more dorsal locations of the STN. These results demonstrate that articulator-specific speech information is contained within high gamma activity of the STN, with similar temporal but less specific topographical organization, compared to similar information encoded in the sensorimotor cortex.\n\nSIGNIFICANCE STATEMENTClinical and electrophysiological evidence suggests that the subthalamic nucleus is involved in speech, however, this important basal ganglia node is ignored in current models of speech production. We previously showed that subthalamic nucleus neurons differentially encode early and late aspects of speech production, but no previous studies have examined subthalamic functional organization for speech articulators. Using simultaneous local field potential recordings from the sensorimotor cortex and the subthalamic nucleus in patients with Parkinsons disease undergoing deep brain stimulation surgery, we discovered that subthalamic nucleus high gamma activity tracks speech production at the level of vocal tract articulators, with high gamma power beginning to increase prior to the onset of vocalization, similar to cortical articulatory encoding.

neuroscience↗

bioRxiv2018

Cortico-basal-ganglia communication: Temporally structured activity for selective motor control

Despite the hard-wired structural connectivity of neural pathways, neural circuits allow context-dependent reactions to sensory cues by triggering the desired movement. Cortico-basal-ganglia circuits seem particularly important for flexible motor control as this is impaired in Parkinsons disease (PD). We analysed subthalamic nucleus (STN) spike and cortical ECoG activity from PD patients performing a visually-cued hand grip task. Fast reaction times were preceded by enhanced STN spike-to-cortical gamma phase coupling irrespective of firing rate changes, suggesting a role of gamma coupling in motor preparation. STN spike timing was offset by half a cycle when comparing ipsilateral with contralateral movements. Additionally, cortical high-frequency activity increased more steeply within each gamma cycle at the sites that showed the strongest coupling with STN spikes. Cortico-basal-ganglia gamma coupling may thus help shape neural activity to facilitate selective motor control. The observation that this effect occurs independent of changes in mean firing rate has far-reaching implications.\n\nHighlightsO_LIFast RTs were preceded by enhanced STN spike-to-cortical gamma phase coupling\nC_LIO_LISTN spike probability was significantly modulated relative to the gamma cycle\nC_LIO_LIDuring ipsilateral movement, spikes were more likely at the opposite part of the cycle\nC_LIO_LISTN output may thus help shape cortical gamma for selective motor control\nC_LI

neuroscience↗

bioRxiv2018

The left midfusiform gyrus interacts with early visual cortex and the anterior temporal lobe to support word individuation.

The left mid-ventral temporal cortex (lmVTC) plays a dynamic role in reading. In this study we investigated the neural interactions that influence lmVTC dynamics and the lexical information these interactions are dependent on. We monitored activity with either intracranial electroencephalography or magnetoencephalography while participants viewed real words, pseudowords, consonant strings, and false fonts. A coarse level representation in early lmVTC activity allowed for decoding of visually dissimilar real words, pseudowords, and false fonts. Functional interactions between anterior ventral temporal regions, possibly containing stored knowledge about words, and low-order visual regions occurred after this initial stage of processing and was followed by the individuation of orthographically similar real words in lmVTC, but not similar pseudowords, letter strings, or false fonts. These results suggest that the individuation of real word representations in lmVTC is catalyzed by stored knowledge about word forms that emerges from network-level interactions with anterior regions of the temporal lobe.

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bioRxiv2018

Modulation of electrocorticographic seizure features predicts response to closed-loop brain stimulation

Why does closed-loop invasive brain stimulation improve seizure control in some patients with epilepsy, but not others? The RNS System, the only FDA-approved bi-directional brain-computer interface, has been shown to improve seizure control in patients with refractory epilepsy, although the mechanisms behind this success are undefined. We analyzed recordings from the RNS System and discovered two main categories of electrophysiological signatures of stimulation-induced modulation of the seizure network. Direct effects included ictal inhibition and early frequency modulation but did not correlate with improved clinical outcomes. Only indirect effects, those occurring remote from triggered stimulation, predicted improved clinical outcomes. These indirect effects, which included spontaneous ictal inhibition, frequency modulation, fragmentation, and ictal duration modulation, may reflect progressive local epileptogenic network compartmentalization that hinders the spread of pathological synchrony from recruiting neuronal populations. Our findings suggest that responsiveness to RNS may be explained by chronic stimulation-induced modulation of seizure network activity, rather than direct effects on each detected seizure.

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bioRxiv2018

Sensorimotor cortical-subthalamic network dynamics during force generation

The subthalamic nucleus (STN) is proposed to participate in pausing, or alternately, in dynamic scaling of behavioral responses, roles that have conflicting implications for understanding STN function in the context of deep brain stimulation (DBS) therapy. To examine the nature of event-related STN activity and subthalamic-cortical dynamics, we performed primary motor and somatosensory electrocorticography while subjects (n=10) performed a grip force task during DBS implantation surgery. The results provide the first evidence from humans that STN gamma activity can predict activity in the cortex both prior to and during movement, consistent with the idea that the STN participates in both motor planning and execution. We observed that STN activity appeared to facilitate movement: while both movement onset and termination both coincided with STN-cortical phase-locking, narrow-band gamma power was positively correlated with grip force, and event-related causality measures demonstrated that STN gamma activity predicted cortical gamma activity during movement. STN participation in somatosensory integration also was demonstrated by casual analysis. Information flow from the STN to somatosensory cortex was observed for both beta and gamma range frequencies, specific to particular movement periods and kinematics. Interactions in beta activity between the STN and somatosensory cortex, rather than motor cortex, predicted PD symptom severity. Thus, the STN contributes to multiple aspects of sensorimotor behavior dynamically across time.

neuroscience↗

bioRxiv2018

Posterior and Mid-Fusiform Contribute to Distinct Stages of Facial Expression Processing

Though the fusiform is well-established as a key node in the face perception network, its role in facial expression processing remains unclear, due to competing models and discrepant findings. To help resolve this debate, we recorded from 17 subjects with intracranial electrodes implanted in face sensitive patches of the fusiform. Multivariate classification analysis showed that facial expression information is represented in fusiform activity, in the same regions that represent identity, though with a smaller effect size. Examination of the spatiotemporal dynamics revealed a functional distinction between posterior and mid-fusiform expression coding, with posterior fusiform showing an early peak of facial expression sensitivity at around 180 ms after subjects viewed a face and mid-fusiform showing a later and extended peak between 230 - 460 ms. These results support the hypothesis that the fusiform plays a role in facial expression perception and highlight a qualitative functional distinction between processing in posterior and mid-fusiform, with each contributing to temporally segregated stages of expression perception.

neuroscience↗

bioRxiv2017

Subthalamic nucleus neurons differentially encode early and late aspects of speech production

Basal ganglia-thalamocortical loops mediate all motor behavior, yet little detail is known about the role of basal ganglia nuclei in speech production. Using intracranial recording during deep brain stimulation surgery, we tested the hypothesis that the firing rate of subthalamic nucleus neurons is modulated in response to both planning and motor execution aspects of speech. Nearly half of 79 recorded units exhibited firing rate modulation, during a syllable reading task administered in 12 subjects. Trial-to-trial timing of changes in subthalamic neuronal activity, relative to cue onset versus production onset, revealed that locking to cue presentation was associated more with units that decreased firing rate, while locking to speech onset was associated more with units that increased firing rate. These uniquely acquired data indicate that subthalamic activity is dynamic during the production of speech, reflecting temporally-dependent inhibition and excitation of separate populations of subthalamic neurons.

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