Dr. Annette Schmid
Human Movement and Balance Unit,
Institute of Neurology,
University College London
will speak on
A fMRI Study of Anticipation and Learning in Smooth Pursuit Eye Movements
Abstract:
Smooth pursuit eye movements to predictable visual stimuli presented in
the dark lead not only to improved tracking accuracy but also to
anticipatory responses. In a functional magnetic imaging (fMRI) study of
human volunteers (n=5) with simultaneous eye movement recording, such
predictable conditions were achieved by an audio-cued, repeated
presentation of a white dot moving at constant velocity (20o or 40o s-1,
to the left or right). After 3 to 4 of the 10 presentations per condition
the stimulus evoked a steady state response in which anticipatory smooth
eye movements were initiated up to 300ms before stimulus onset. This was
contrasted to smooth pursuit in a nonpredictable situation where timing of
the audio cue, the velocities and directions were balanced but
pseudo-randomised. This abolished the anticipation and improvement in
tracking. In a control condition subjects were asked to gaze at the centre
of the projection screen.
The fMRI images were analyzed with the SPM99 software package for fixed
effects of the 24s epochs per condition using mean and exponential decay
functions to model changes in the blood oxygenation level dependent (BOLD)
signal. Comparison of smooth pursuit with the control condition revealed
statistical parametric maps in a network of brain areas known to be
involved in visuomotor tasks and motion processing including prefrontal,
premotor, medial temporal, parietal and cerebellar areas. While
activations in the dorsolateral prefrontal cortex and the parietal areas
around the intraparietal sulcus increased with time (p<0.001, corrected
for multiple comparisons) during nonpredictable conditions, the anterior
cingulate and preSMA showed an increase in activation during predictable
epochs (pcluster= 0.015 and 0.003 respectively). These changes in
activation over time may be associated with a type of short-term learning
of the timing and eye movement trajectory and are reminiscent of findings
in other types of motor and sequence learning. Intriguingly, the
experiment revealed also a clear correlation of activation in the cuneus
with the contraversive eye movement condition (p<0.001, corrected for
multiple comparisons).
The lecture will take place in the
Lecture Hall, Room 203, 44 Cummington St.
on Thursday, August 3, 2000
at 11:00 am
Hosted by the
Brain and Vision Research Laboratory