Jared Medina

Post-Doctoral Fellow
jared [dot] medina (AT) uphs [dot] upenn [dot] edu
Department of Neurology
Center for Cognitive Neuroscience
University of Pennsylvania

Education

Ph.D., 2006: Cognitive Science, Johns Hopkins University

• Dissertation: Somatosensory frames of reference

• Master's Thesis: Representational dynamism in the somatosensory hand representation subsequent to cerebral lesion

Research

My research focuses on understanding the functional and neural architecture of the mind and brain using methodology from cognitive neuropsychology and cognitive neuroscience. In particular, I am interested in understanding body and spatial representations.

In work with Professor Brenda Rapp, I have examined how the location of a tactile stimulus is represented, using evidence from single-case studies of stroke patients. In patients with damage to somatosensory regions of the brain, we found systematic errors in localization of tactile stimuli presented to the hand. More specifically, perceived locations were shifted towards the center of the hand yet maintained the relative topography of the pre-lesion experience (Rapp, Hendel, & Medina, 2002 , PDF). We also found that this shifted topography could be altered by stimulating the forearm prior to a localization judgment. (Medina & Rapp, in preparation). The altered localization ability is thought to reflect increased plasticity after lesion in spatial representations for tactile localization. In another case study, we report a subject (DLE) who presented with a phenomenon known as synchiria: When stimulated on the ipsilesional side of the body, he perceived stimuli on both sides of the body (Medina & Rapp, in press). Remarkably, DLE was more "accurate" at localizing the phantom synchiric percept than localizing actual stimuli presented to his contralesional hand. This study provides evidence for precise connections between representations of homologous body regions in the two hemispheres, and suggests that phantom synchiric percepts may be due to removal of intrahemispheric inhibition.

My research has also investigated the representation of location in various frames of reference, in both tactile and visual domains. One synchiric subject exhibited a pattern of increased synchiria as his hands moved from ipsilesional to contralesional space in both trunk- and head-centered frames of reference (Medina & Rapp, in press). These results provide evidence that the cross-hemispheric connections that give rise to phantom synchiric percepts are inhibited by representations that operate in body-centered reference frames. I have also examined the reference frame of tactile representations in a novel application of the Simon effect paradigm with neurologically intact subjects (Medina & Rapp, in preparation). I found that when subjects’ arms are uncrossed, they demonstrate a Simon effect based on an allocentric, object-relative reference frame. However, when their arms are crossed, they exhibit a Simon effect based on an egocentric, somatotopic reference frame (e.g., the left hand is encoded as left, regardless of position). We found that egocentric neglect

Furthermore, I have collaborated with Professor Argye Hillis to explore the neural correlates of different sub-types of visual neglect (e.g., viewer-centered neglect, stimulus-centered neglect, etc.). We studied a series of acute right-hemisphere patients, using both behavioral data and magnetic resonance perfusion-weighted and diffusion-weighted imaging to correlate regions of hypoperfusion and/or infarct with different subtypes of neglect. We found that right supramarinal gyrus and more dorsal brain regions are involved in egocentric processing, whereas right posterior inferior temporal gyrus and other more ventral regions are involved in allocentric processing (Medina et al., in press).

I am currently examining the interaction of body representations with motor systems, in research with Professor Branch Coslett. First, we have examined the ability of individuals with severe proprioceptive deficits (due to a peripheral deafferentation) in reaching tasks. In one study, we presented a deafferented subject with a double jump task, in which she (hand unseen) was instructed to reach to a target that remains stationary or "jumps" to another location (Medina et al., submitted). Without vision or proprioception, our subject used information from a copy of the motor plan (efference copy) during the initial movement segment to make accurate turns to the target. However, she was very inaccurate at judging the correct endpoint of her movement, providing evidence that information from efference copy is available to direct movements during the initial, but not terminal, phase of movement. We have also explored the neural correlates of sensory feedback and motor information in localizing a body part without vision, comparing localization performance with (active movement) and without (passive movement) information from efference copy, using permutation analyses in conjunction with voxel lesion symptom mapping analyses. We have found that the right angular gyrus is important in representing limb location after passive movement, whereas damage to left premotor cortex is associated with limb localization after active movement (Medina, Jax & Coslett, submitted).

Publications

• Medina, J. & Rapp, B. (in press). Phantom tactile sensations modulated by body position. Current Biology.
• Medina, J., Kannan, V., Pawlak, M., Kleinman, J., Newhart, M., Davis, C., Heidler-Gary, J., Herskovits, E., & Hillis, A. (in press). Neural substrates of visuospatial processing in distinct reference frames: Evidence from unilateral spatial neglect. Journal of Cognitive Neuroscience.
• Rapp, B., Hendel, S.K., & Medina, J. (2002). Remodeling of somatosensory hand representations following cerebral lesions in humans. Neuroreport, 13, 207-211. (PDF)
• Medina, J., Jax, S.A., & Coslett, H.B. (under review). Maintenance of Internal Models Requires Proprioception: Evidence from Deafferentation.
• Medina, J., Jax, S.A., Brown, M.J., & Coslett, H.B. (under review). Efference Copy Access in Initial but not Terminal Stages of Movement: Evidence from Deafferentation.
• Medina, J., Jax, S.A., & Coslett, H.B. (under review). Representing limb location: Neural substrates of predicted state and sensory state information.
• Medina, J., & Rapp, B. (in preparation). Somatotopic and non-somatotopic frames of reference – Evidence from the Simon effect.
• Medina, J., & Rapp, B. (in preparation). Representational dynamism in the somatosensory hand representation subsequent to cerebral lesion.

Presentations

• Coslett, H.B. & Medina, J. (2007). Reaching with and without vision after deafferentation. Poster presented at the 37th Annual Meeting of the Society for Neuroscience, San Diego.
• Medina, J. & Rapp, B. (2007). Multiple somatosensory frames of reference: Evidence from the Simon effect. Poster presented at the 48th Annual Meeting of the Psychonomic Society, Long Beach.
• Medina, J., Jax, S.A., & Coslett, H.B. (2007). Reaching to moving targets after deafferentation. Poster presented at Progress in Motor Control VI, Santos, Brazil.
• Medina, J., Jax, S.A., & Coslett, H.B. (2007). Representing Effector Location: Contributions of Predicted State and Sensory State Information. Poster presented at the 14th annual meeting of the Cognitive Neuroscience Society, New York City.
• Medina, J., & Rapp, B. (2006). Somatosensory Frames of Reference: A Case of Tactile Synchiria. Talk given at the Tactile Research Group meeting, Houston.
• Medina, J., & Rapp, B. (2006). Tactile Perception Modulated by Body Position. Poster presented at the 13th Annual Meeting of the Cognitive Neuroscience Society, San Francisco.
• Medina, J., & Rapp, B. (2004). A Case of Tactile Synchiria: Preserved Somatotopy? Poster presented at the 32nd Annual Meeting of the International Neuropsychological Society, Baltimore.
• Medina, J., & Hillis, A. (2003). Using MR perfusion and diffusion imaging to identify neural substrates of specific types of unilateral spatial neglect. Talk given at the Joint International Conference on Cognitive Science, Sydney.
• Medina, J., & Hillis, A. (2003). Identifying neural regions for distinct types of unilateral spatial neglect using MR perfusion and diffusion imaging. Talk given at the IGERT Student Research Symposium, Pittsburgh.
• Medina, J., & Hillis, A. (2003). Neural Substrates of Distinct Patterns of Unilateral Spatial Neglect. Poster presented at the 10th annual meeting of the Cognitive Neuroscience Society, New York City.
• Medina, J., Barker, P., Jacobs, M., Wityk, R., & Hillis, A. (2003). Neural Substrates of Specific Types of Unilateral Spatial Neglect: Evidence from MR Perfusion and Diffusion Imaging. Talk given by A. Hillis at the 55th Annual Meeting of the American Academy of Neurology, Honolulu.
• Medina, J., & Rapp, B. (2002). The plasticity of somatosensory representations following cerebral lesions in adult humans. Poster presented at the 9th annual meeting of the Cognitive Neuroscience Society, San Francisco.

Teaching

• Fall 2000: T.A., Language & Mind, Dr. Bill Badecker
• Fall 2001: T.A., Introduction to Cognitive Neuropsychology, Dr. Michael McCloskey
• Spring 2002: T.A., Cognitive Neuroscience: Exploring the Living Brain, Dr. Brenda Rapp
• Spring 2002: T.A., Topics in Neuroscience, Dr. Michael Steinmetz
• Fall 2002: T.A., Foundations in Cognitive Science, Dr. Paul Smolensky
• Spring 2003: T.A., Cognitive Neuroscience: Exploring the Living Brain, Dr. Brenda Rapp
• Fall 2003: T.A., Reading and Writing: Normal Processing and Disorders, Dr. Brenda Rapp
• Spring 2004: T.A., Cognitive Neuroscience: Exploring the Living Brain, Dr. Brenda Rapp
• Supervision of six undergraduates doing research in cognitive neuropsychology.