Integrative cortical dysfunction and pervasive motion perception deficit in fragile X syndrome.
BACKGROUND
Fragile X syndrome (FXS) is associated with neurologic deficits recently attributed to the magnocellular pathway of the lateral geniculate nucleus.


OBJECTIVE
To test the hypotheses that FXS individuals 1) have a pervasive visual motion perception impairment affecting neocortical circuits in the parietal lobe and 2) have deficits in integrative neocortical mechanisms necessary for perception of complex stimuli.


METHODS
Psychophysical tests of visual motion and form perception defined by either first-order (luminance) or second-order (texture) attributes were used to probe early and later occipito-temporal and occipito-parietal functioning.


RESULTS
When compared to developmental- and age-matched controls, FXS individuals displayed severe impairments in first- and second-order motion perception. This deficit was accompanied by near normal perception for first-order form stimuli but not second-order form stimuli.


CONCLUSIONS
Impaired visual motion processing for first- and second-order stimuli suggests that both early- and later-level neurologic function of the parietal lobe are affected in Fragile X syndrome (FXS). Furthermore, this deficit likely stems from abnormal input from the magnocellular compartment of the lateral geniculate nucleus. Impaired visual form and motion processing for complex visual stimuli with normal processing for simple (i.e., first-order) form stimuli suggests that FXS individuals have normal early form processing accompanied by a generalized impairment in neurologic mechanisms necessary for integrating all early visual input.
Kogan
C S
CS
Department of Psychology, 1205 Dr. Penfield Avenue, Stewart Biologic Sciences Building, Room W8/1, McGill University, Montréal, Québec, H3A 1B1, Canada. cary@hebb.psych.mcgill.ca
Bertone
A
A
Cornish
K
K
Boutet
I
I
Der Kaloustian
V M
VM
Andermann
E
E
Faubert
J
J
Chaudhuri
A
A
D000293:Adolescent; D000328:Adult; D005600:Fragile X Syndrome / Q000503:physiopathology*; D005829:Geniculate Bodies / Q000503:physiopathology; D006801:Humans; D008297:Male; D009039:Motion Perception; D009778:Occipital Lobe / Q000503:physiopathology; D010296:Parietal Lobe / Q000503:physiopathology*; D012684:Sensory Thresholds; D013702:Temporal Lobe / Q000503:physiopathology*; D014795:Visual Pathways; D014796:Visual Perception