Download The effect of visual experience on the development of the mirror

Visual experience is not necessary for the development of the mirror neuron system in the
human brain
Emiliano Ricciardi
Laboratory of Clinical Biochemistry and Molecular Biology, University of Pisa Medical School,
Pisa, Italy
A particular class of visuomotor neurons in humans, discovered originally in the monkey premotor
cortex and called mirror neurons, discharges both when subjects perform a goal-directed action
and when they observe another individual performing a similar action. Furthermore, several pieces
of evidence support the existence of a particular subclass of mirror neurons, defined auditory-visual
mirror neurons (AV-MNS), that allows to understand the actions of other individuals by hearing the
sound of a specific action (Gazzola et al., Curr Biol, 2006). A crucial question is whether this
activity in the AV-MNS is merely mediated by a visual imagery representation of a given action or
is truly engaged by auditory perception. To address this question we investigated brain response to
visual and/or auditory perception of different stimuli in sighted and congenitally blind individuals.
Using an fMRI (GE Signa 1.5 Tesla scanner) sparse sampling block design we examined neural
activity in 7 congenitally blind and 12 sighted right-handed healthy volunteers while they were
presented with action/environmental sounds or movies, and performed an odd-ball motor testing
paradigm. Both congenitally blind and sighted individuals during the listening (and the observation
for sighted only) of actions performed by others activated a left lateralized network including the
superior and middle temporal gyri, the inferior parietal lobule and the inferior frontal premotor
cortex. These results indicate that sighted and congenitally blind subjects similarly activate the AVMNS, and suggest that visual experience is not a necessary prerequisite for the development of the
neural functional architecture for action recognition of other individuals. These findings further
expand previous data indicating that representation of the external world relies on supramodal
cortical association areas (Pietrini, this symposium) and may contribute to explain why individuals
who have had no visual experience interact effectively with the surrounding environment.
Neural correlates of mental representation of space in sighted and blind individuals
Daniela Bonino
Laboratory of Clinical Biochemistry and Molecular Biology, University of Pisa Medical School,
Pisa, Italy
Visual perception and visual imagery share common cortical regions within the parietal lobes. The
extrastriate cortex of the dorsal pathway for spatial localization can process stimuli independently
from the sensory modality that conveys the information to the brain and thus appears to be
organized in a supramodal fashion. Here we tested the hypothesis that the neural mechanisms that
subserve spatial imagery also might be supramodal in nature. We used fMRI (GE Signa 1.5 Tesla
scanner) to examine neural activity in 10 sighted and 7 congenitally blind right-handed healthy
volunteers while they performed a modified version of the mental clock task in three distinct
conditions. During an auditory condition, subjects were asked to imagine two analogue clock faces
showing the times that were indicated verbally, and to judge in which case the clock hands formed
the wider angle. During the visual and tactile angle discrimination conditions, participants
compared pairs of clock faces presented visually or tactilely and decided which hand set formed the
wider angle. During the auditory imagery condition, both the sighted and congenitally blind
individuals showed significant activations in posterior parietal areas, including the intraparietal
sulcus and the inferior parietal lobule. These same areas showed significant activations also during
the tactile and visual angle discrimination conditions. As expected, auditory, visual and tactile
primary sensory regions also were activated during the respective conditions. Ventral occipital brain
areas additionally were recruited in blind as compared to sighted subjects during both the tactile and
auditory tasks. Both spatial discrimination and spatial imagery representation occur in the posterior
parietal extrastriate cortex also when spatial stimuli are not visual in nature. This may also explain
how people who have had no visual experience are able to form appropriate mental spatial
representations about their surroundings, and thus interact effectively with the environment.