Research projects

 

 

Neural and Behavioral Correlates of Speech and Language Impairments in Parkinson's Disease

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Parkinson's disease (PD) is associated with impairments in a wide range of motor and cognitive functions. Using electroencephalography (EEG),  we examine the neural mechanisms of speech, voice and language disorders in patients with PD.

 

Publications (* indicates equal contributions)

  1. Rohl A, Gutierrez S, Johari K, Greenlee J, Tjaden K, Roberts A. Speech Dysfunction, Cognition, and Parkinson's Disease. Progress in Brain Research (2022).
  2. Kopf L, Rohl A, Nagao T, Bryant K, Johari K, Tjaden K, Greenlee J. Voice Handicap Index in Parkinson’s Patients: Subthalamic versus Globus Pallidus Deep Brain Stimulation. Journal of Clinical Neuroscience (2022).
  3. Johari K, Behroozmand R. Neural Correlates of Speech and Upper Limb Motor Timing Deficits Revealed by Aberrant Beta Band Desynchronizations in Parkinson’s Disease. Clinical Neurophysiology (2021).
  4. Reifegerste J, Estabrooke IV, Russell LE, Veríssimo J, Johari K, Wilmarth B, Pagan FL, Moussa C & Ullman. Can Sex Influence the Neurocognition of Language? Evidence from Parkinson's Disease. Neuropsychologia (2020).
  5. Johari K, Walenski M, Reifegerste J, Ashrafi F & Ullman M.T. Sex, Dopamine, and Hypokinesia: A Study of Inflectional Morphology in Parkinson’s Disease. Neuropsychology (2019).
  6. Johari K, Walenski M, Reifegerste J, Ashrafi F, Behroozmand R, Daemi M, Ullman MT. A Dissociation between Syntactic and Lexical Processing in Parkinson’s Disease. Journal of Neurolinguistics (2019).
  7. Behroozmand R*, Johari K*. Pathological Attenuation of the Right Prefrontal Cortex Activity Predicts Speech and Limb Motor Timing Disorder in Parkinson’s Disease. Behavioural Brain Research (2019).
  8. Behroozmand R*, Johari K*. Sensorimotor Impairment of Speech and Hand Movement Timing Processing in Parkinson’s Disease. Journal of Motor Behavior (2018).

 

The role of subcortical structures in speech and limb motor control

We investigate the role of subcortical structures ins speech and limb motor control.  Deep brain stimulation surgery provides a great opportunity to collect Local field potentials and  spike activity  associated with speech and, voice and limb movement in patients with PD and essential tremor. 

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Publications (* indicates equal contributions)

  1. Tabari F, Flouty O, Greenlee J, Berger J& Johari K. Speech, Voice, and Language Outcomes Following Deep Brain Stimulation in Parkinson’s Disease and Essential Tremors: A Systematic Review of Literature.  Plos One(In Press).
  2. Johari K, Berger J, Rohl A,&Greenlee J.Dissociation Between Simple and Complex Speech Motor Tasks Within Bilateral Motor Thalamus ( under review) 
  3. Johari K, Kelley R*, Tjaden K, Patterson C, Rohl A, Berger J, Corcos D & Greenlee J. Subthalamic Nucleus Neurons Differentially Encode Speech and Limb Movement in Parkinson's Disease. Frontiers in Human Neuroscience (2023).
  4. Berger J, Johari K, Kovach C & Greenlee J. Speech Artifact is also Present in Spike Data. Neuroimage (2022).

 

The Application of Non-Invasive Brain Stimulation to Improve Speech and Language Functions
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Non-invasive brain stimulation techniques such as transcranial alternating/direct current stimulation hold a promise to modulate cortical activity and improve motor and non-motor functions in neurotypical adults and individuals with neurological conditions. We use  HD-tDCs /tACS along with EEG to establish and develop non-invasive protocols that could help patients with Parkinson’s disease.  The current projects have been funded by the Louisiana Board of Regents grant. 

 

Publications

  1. Johari K & Joel Berger. Theta Oscillations within Right Dorsolateral Prefrontal Cortex Contribute Differently to Speech vs. Limb Inhibition. Journal of Neuroscience Research (2024).
  2. Johari K, Berger J. High-Definition Transcranial Direct Current Stimulation Over Right Dorsolateral Prefrontal Cortex Differentially Modulates Inhibitory Mechanisms for Speech vs. Limb Movement. Psychophysiology (2023).
  3. Johari K, Tabari F& Desai, R. Right Frontal HD-tDCS Reveals Causal Involvement of Time perception Networks in Temporal Processing of Concepts. Scientific Reports (2023).
  4. Johari K, Riccardi N, Malyutina S, Modi M & Desai R. HD-tDCS of Primary and Higher-order Motor Cortex Affects Action Word Processing. Frontiers in Human Neuroscience (2022).
  5. Johari K, Riccardi N, Malyutina S, Modi M, Desai R. HD-tDCS over Motor Cortex Facilitates Action Sentence Processing. Neuropsychologia (2021).
  6. Behroozmand R, Johari K, Bridwell K, Hayden C, Fahey D, den Ouden DB. Modulation of Vocal Pitch Control through High-Definition Transcranial Direct Current Stimulation of the Left Ventral Motor Cortex. Experimental Brain Research (2020).

 

Sensory-Motor Systems Involvement in Conceptual Processing

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We use behavioral measures, HD-tDCS, and EEG to examine the motor-language coupling in action word processing in neurotypical adults and patients with Parkinson’s disease. These studies provided the causal and clinical evidence that action-related words are grounded in the motor system and have clinical implications for Parkinson’s disease, wherein action word processing is significantly compromised. As a part of the Louisiana Board of Regents grant, we have been studying the efficacy of HD-tACS on improving neural and behavioral markers of action word processing in PD patients and neurotypical adults. This work also has been supported by an R01 NIH grant awarded to Dr. Rutvik Desai at the University of South Carolina. 

 

Publications

  1. Johari K, Tabari F& Desai, R. Right Frontal HD-tDCS Reveals Causal Involvement of Time perception Networks in Temporal Processing of Concepts. Scientific Reports (2023).
  2. Johari K, Lai V, Riccardi N & Desai R. Temporal Features of Concepts Are Grounded in the Time Perception Neural Networks: An EEG study. Brain & Language (2023).
  3. Johari K, Riccardi N, Malyutina S, Modi M & Desai R. HD-tDCS of Primary and Higher-order Motor Cortex Affects Action Word Processing. Frontiers in Human Neuroscience (2022).
  4. Johari K, Riccardi N, Malyutina S, Modi M, Desai R. HD-tDCS over Motor Cortex Facilitates Action Sentence Processing. Neuropsychologia (2021).
  5. Johari K, Walenski M, Reifegerste J, Ashrafi F, Behroozmand R, Daemi M, Ullman MT. A Dissociation between Syntactic and Lexical Processing in Parkinson’s Disease. Journal of Neurolinguistics (2019).