Biology subjects

Dickey, M. W.

Publications and source records attributed to Dickey, M. W..

5 recordsLinked to original sources

bioRxiv2026

Concept-Level Semantic Representations Remain Decodable in Chronic Post-Stroke Aphasia

Aphasia is characterized by impaired word retrieval, yet most cognitive models of word production assume that underlying conceptual-semantic representations are largely preserved. This study investigated whether concept-level semantic structure remains decodable from BOLD signals in chronic post-stroke aphasia and which semantic models best explain neural representational geometry during covert semantic feature generation. Eight healthy adults and six individuals with chronic aphasia completed a dense-sampling fMRI protocol in which they viewed 57 pictured nouns while silently generating semantic features. Representational similarity analysis showed that an experiential model (Exp48) best matched neural geometry in both people with aphasia and controls, outperforming taxonomic (WordNet) and distributional (Word2Vec, GloVe) models. Using representational similarity decoding, concept identity was recovered well above chance in both groups. No relationship was found between decoding accuracy and language measures from individuals with aphasia. These findings suggest that experiential semantic structure remains robustly represented and decodable in chronic aphasia despite lesion-related language impairments, highlighting preserved conceptual representations alongside altered anatomy.

neuroscience↗

bioRxiv2020

White matter neuroanatomical predictors of aphasic verb retrieval

BackgroundCurrent neurocognitive models of language function have been primarily built from evidence regarding object naming, and their hypothesized white matter circuit mechanisms tend to be coarse-grained. MethodsIn this cross-sectional, observational study, we used novel correlational tractography to assess the white matter circuit mechanism behind verb retrieval, measured via action picture-naming performance in adults with chronic aphasia. ResultsThe analysis identified tracts implicated in current neurocognitive dual-stream models of language function, including the left inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, and arcuate fasciculus. However, the majority of tracts associated with verb retrieval were not ones included in dual-stream models of language function. Instead, they were projection pathways that connect frontal and parietal cortices to subcortical regions associated with motor functions, including the left corticothalamic pathway, frontopontine tract, parietopontine tract, corticostriatal pathway, and corticospinal tract. ConclusionsThese results highlight that cortico-subcortical projection pathways implicated in motor functions may be importantly related to language function. This finding is consistent with grounded accounts of cognition and may furthermore inform neurocognitive models. Impact StatementThis study suggests that in addition to traditional dual-stream language fiber tracts, the integrity of projection pathways that connect frontal and parietal cortices to subcortical motor regions may be critically associated with verb-retrieval impairments in adults with aphasia. This finding challenges neurological models of language function.

neuroscience↗

bioRxiv2020

Thalamic encoding of lexical status is lateralized during reading aloud

To explore whether the thalamus participates in lexical status encoding, local field potentials were recorded in patients undergoing deep brain stimulation lead implantation while they read aloud single-syllable words and nonwords. Bilateral decreases in thalamic beta (12-30Hz) activity were preferentially locked to stimulus presentation, and these decreases were greater when nonwords were read. Increased broadband gamma (70-150Hz) activity also was locked preferentially to speech onset bilaterally, but greater nonword-related increases in this activity were observed only on the left, demonstrating lateralization of thalamic gamma selectivity for lexical status. In addition, this lexical status effect was strongest in more anterior thalamic locations, regions which are more likely to receive pallidal than cerebellar afferents. These results provide evidence from intracranial thalamic recordings for the lateralization and topography of subcortical lexical status processing.

neuroscience↗

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↗

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.

neuroscience↗