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
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, 2002, PPT). 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, 2004, PPT). 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, 2005, PPT). 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. 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).
Furthermore, I am currently collaborating 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 are
studying 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. (Medina
& Hillis, 2003, PPT).
I am currently examining the interaction of body representations with
motor systems, in research with Professor Branch Coslett. I 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. Without vision or proprioception, our subject used
information from the motor plan (specifically, movement distance) 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 the motor plan is
available to direct movements during the initial, but not terminal, phase
of movement. We are also exploring the neural correlates of sensory
feedback and motor information in localizing a body part without vision,
comparing localization performance with and without information from a
motor plan, using permutation analyses in conjunction with voxel lesion
symptom mapping analyses (Medina,
Jax, & Coslett, 2007, PPT).
Publications
Download CV (PDF)
Presentations
Teaching
Coursework