Functional neuroanatomy
of visual event detection requiring foot and hand responses: An event-related fMRI study
Francis X. Graydon, Mark D. Benton
Brain Research and Imaging Neuroscience Division,
Objective: Previous fMRI studies of human
motor system functioning have focused almost exclusively on motor processes
associated with the hand or wrist (i.e. upper limb) such as movement
preparation, planning, execution and motor learning. Recently, researchers have
extended the use of fMRI to disclose the functional neuroanatomy of foot and ankle movements (i.e. lower limb).
In the current study, we were interested in defining the neural networks
associated with hand and foot responses during a visual-event detection task
that one might encounter in a real word scenario (e.g. driving). We predicted
that while hand and foot responses to the target visual events would show
unique somatotopy, both would activate a shared
network of motor regions, including the parietal cortex.
Methods: Seven healthy right handed and footed participants (4 women, 3
men, age 20-30) took part in the study. Subjects were imaged (BOLD EPI) as they
responded with their dominant (right) hand or foot to target visual events that
appeared in the center (C) or left periphery (P) of simple (black background)
or complex (driving video) visual conditions. The order of the conditions was
counterbalanced across subjects. An event related design was used such that
during each of the 4 experimental conditions, subjects responded to 60 center (C) and 60 peripheral (P) target visual events. These
120 events were combined with 60 null events (no stimulus, no response) for a
total of 180 events. Events were presented randomly with an inter-stimulus interval
(ISI) of 2.5 s. Image processing and statistical analysis was performed in
SPM2.
Results & Discussion: Response times for the foot were significantly
slower in the simple (593±93 ms v 400±28 ms) and complex (618±60 ms v 469±46
ms) conditions. Foot responses activated a network of cortical and subcortical regions that included: anterior cingulate (BA 24), premotor
cortex, supplementary motor area (SMA), dorsolateral
prefrontal cortex (DLPFC) (BA 9, 46), post central gyrus
(BA 2,5), inferior parietal lobules, superior temporal
gyrus, cerebellum, and putamen.
No significant foot response time differences were found between C and P events
in the simple visual condition. Foot responses were significantly slower for
peripheral events during the driving video (t = 6.80, p < .002) and
were associated with increased activation in the anterior cingulate
(BA 32), lingual gyri, cerebellum, cuneus and precuneus. Compared to
the hand, foot event detection showed greater involvement of the SMA, motor
cortex, anterior and posterior cingulate, paracentral lobule, post central gyrus
(BA 5), superior temporal gyrus, and cerebellum
during the driving video (complex) condition.
Conclusions: The network of foot regions identified
are consistent with those reported for cued foot flexion-extension
movements (Sahyoun et al. 2004). However, they also
show a role for the inferior parietal lobules not previously reported. This
study highlights the need to extend event detection paradigms to include pedal
and multi-limb responses. This will improve our ability to understand key brain
networks engaged during critical event detection performed within human
operator environments, as well as motor impairments in different clinical
populations.
References & Acknowledgements: Sahyoun C
et al. Neuroimage 21, 568 (2004).