Angela Hewitt

Ph.D. 2013

E-MAIL: hewit051@umn.edu

View CV

Thesis Title:

Does cerebellar cortex function as a forward internal model for motor control?

Current Position:

Child Neurology MD Resident, Mayo Clinic

Undergraduate Institution and Major/Degree:

  • M.S. Biomedical Engineering, May 2005
    Area of Emphasis: Neuromusculoskeletal Movement
    University of Wisconsin-Madison, Madison, WI
  • B.S. Biomedical Engineering, December 2002
    University of Wisconsin-Madison, Madison, WI

Major Advisor(s):

Timothy J. Ebner, M.D., Ph.D.

Research Description:

Motor control theorists have postulated that production of rapid, coordinated movements requires control circuitry that can bypass sensory feedback delays by providing an estimate of the consequences resulting from a motor command.  This control element, termed a forward internal model, receives an efferent copy of the motor command and information about the current state in order to predict the future state of the limb (i.e, kinematic variables like position and velocity).  Previous pychophysical, imaging, and patient case studies suggest that the cerebellum is a possible location for implementation of an internal model.  However, few electrophysiological studies have investigated whether the firing discharge from cerebellar neurons is consistent with the properties of a forward internal model.  The ultimate goal of this project is to evaluate whether the simple spike firing from Purkinje cells (PCs) in lobules IV-VI of the intermediate/lateral cerebellar zones is consistent with output from a forward internal model.  Although no single result will conclusively prove this hypothesis, two electrophysiology experiments examining hand movements in rhesus macaques are proposed to test several aspects of a forward internal model.  Aim 1 will examine whether PC firing predicts future hand kinematics in a task-independent manner.  Aim 2 will further evaluate model adaptability and whether changing model inputs alters predicted kinematics.  The results will either show that PC firing is incompatible with the output expected from a forward model or provide solid support for future experiments. 

Lab Rotations:

  • Apostolos Georgopoulos
  • Tim Ebner
  • Bin He

Courses Taken Beyond the Core Courses:

  • Medical school courses

Graduate Level Minor:

  • Medicine

Committee Members:

  • Jim Ashe- chair
  • Alvin Beitz
  • Khalaf Bushara
  • Tim Ebner- advisor 

Selected Publications:

  • Popa LS, Streng ML, Hewitt AL, Ebner TJ. The errors of our ways: Understanding error representations in cerebellar-dependent motor learning. Cerebellum. 2016;15(2):93-103.
  • Hewitt AL, Popa LS, Ebner TJ. Changes in Purkinje cell simple spike encoding of reach kinematics during adaption to a mechanical perturbation. J Neurosci. 2015;35(3):1106-24
  • Popa LS, Hewitt AL, Ebner TJ. The cerebellum for jocks and nerds alike. Front Syst Neurosci. 2014 Jun 17;8:113. 
  • Popa LS, Hewitt AL, Ebner TJ. Purkinje cell simple spike discharge encodes error signals consistent with a forward internal model. Cerebellum. 2013 Jun;12(3):331-3.
  • Popa LS, Hewitt AL, Ebner TJ. Predictive and feedback performance errors are signaled in the simple spike discharge of individual Purkinje cells. J Neurosci. 2012;32(44):15345-58
  • Hewitt A, Popa L, Pasalar S, Hendrix C, Ebner T. Representation of limb kinematics in Purkinje cell simple spike discharge is conserved across multiple tasks.  J Neurophysiol. 2011;106:2232-47
  • Ebner T, Hewitt A, Popa L. What features of limb movements are encoded in the discharge of cerebellar neurons?  Cerebellum, 2011;10(4):683-93. 
  • Hewitt A, Hind J, Kays S, Nicosia M, Doyle J, Tompkins W, Gangnon R, Robbins J.  Standardized instrument for lingual pressure measurement. Dysphagia 2007;23:16-25.
  • Robbins J, Kays S, Gangnon R, Hind J, Hewitt A, Gentry L, Taylor A.  The effects of lingual exercise in stroke patients with dysphagia. Arch Phys Med Rehab. 2007;88:150-158.
  • Robbins J, Gangnon R, Theis S, Kays S, Hewitt A, Hind J. The Effects of Lingual Exercise on Swallowing in Older Adults. J Amer Geriat Soc. 2005;53:1483-1489.

Invited Talks:

  • Hewitt A (2011).  “Purkinje Cell Simple Spikes: Simply Encoding Movement Kinematics?”, University of Minnesota MSTP Annual Retreat, Stillwater, MN, July 13.

Awards and Honors:

  • Doctoral Dissertation Fellowship 2012
  • Graduate Program in Neuroscience (GPN) Stark Travel Award 2012
  • GPN Richard Poppele Award 2010
  • GPN Milne-Brandenburg NRSA Achievement Award 2010
  • NINDS / AUPN / ANA Travel award: Combining Clinical and Research Careers in Neuroscience 2009
  • Neuro-physical-computational Sciences (NPCS) Graduate Trainee 2007-09

Conferences Attended and Presentations:

  • Conference Presentations:

  • Popa LS, Streng ML, Hewitt AL, Ebner TJ. The Errors of Our Ways: Understanding Error Representations in Cerebellar-Dependent Motor Learning. Cerebellum. 2015 Jun 26.
  • Hewitt AL, Popa LS, Ebner TJ. Changes in Purkinje Cell Simple Spike Encoding of Reach Kinematics during Adaption to a Mechanical Perturbation. J Neurosci. 2015 Jan 21;35(3):1106-24.
  • Popa LS, Hewitt AL, Ebner TJ. The cerebellum for jocks and nerds alike. Front Syst Neurosci. 2014 Jun 17;8:113. doi: 10.3389/fnsys.2014.00113. eCollection 2014. Review.
  • Hewitt A, Popa L, Ebner T (2012). "Adaptation to force perturbations alters feedforward and feedback signals in Purkinje cell simple spike firing", 22nd Annual Meeting of the Society for the Neural Control of Movement, Venice, Italy, April 22-29.
  • Popa L, Hewitt A, Ebner T (2012). "Individual Purkinje cell simple spike discharge is full of errors", 22nd Annual Meeting of the Society for the Neural Control of Movement, Venice, Italy, April 22-29.
  • Hewitt A, Popa L, Ebner T (2011). "Purkinje cell simple spike firing shows progressive trial by trial changes during adaptation to force perturbations", Society for Neuroscience Annual Meeting, Washington, DC, November 12-16.
  • Popa L, Hewitt A, Ebner T (2011). "Purkinje cell simple spike discharge encodes complex temporal representations of the movement goal", Society for Neuroscience Annual Meeting, Washington, DC, November 12-16.
  • Hewitt A, Popa L, Pasalar S, Hendrix C, Ebner T (2010). "Purkinje cell simple spikes: simply predicting movement Kinematics?", Twentieth Annual Meeting of the Society for the Neural Control of Movement, Naples, FL, April 20-25.
  • Popa L, Hewitt A, Pasalar S, Hendrix C, Ebner T (2010). "Purkinje cell simple spike discharge integrates task error signals with hand kinematics signals", Twentieth Annual Meeting of the Society for the Neural Control of Movement, Naples, FL, April 20-25.

Professional Memberships:

  • Biomedical Engineering Society
  • American Medical Association
  • Society for the Neural Control of Movement (NCM)
  • Society for Neuroscience (SfN)
  • American Academy of Neurology (AAN)
  • Student Interest Group in Neurology, UMN chapter president 2007-2008

Home Town:

  • Chetek, WI
Angela Hewitt