High-density VEP measures of global form and motion processing in infants born very preterm

Abstract

Infants born preterm show a delay in the onset of visual evoked potentials (VEP) for direction reversal, even when their responses to orientation reversal are comparable to term-born infants (Birtles et al, 2007, NeuroReport 18: 1975). Does this developmental difference between form and motion processing extend to the later development of systems responding to global organization in these domains? We tested a group of infants born ≤32 weeks gestation with term born controls, between 4.5–7 months post-term age. Using a 128-channel geodesic sensor net, we recorded high-density steady-state VEPs to (a) motion coherence transitions of a pattern of concentric dot trajectories alternating with randomly directed trajectories; (b) form coherence transitions of a similar pattern in which the dots of each trajectory were plotted simultaneously to form short concentric arcs. As in our earlier work (Braddick et al VSS 2006, 2007) a statistically significant first-harmonic signal was taken as evidence of a neural response to global structure. The control group confirmed our previous findings in showing a substantially lower incidence of global form responses (31% of infants significant) than global motion responses (100%). The preterm group showed a similar proportion with global form responses (42%) but a substantially lower proportion with global motion responses (67%). We conclude that, compared to the global form processing mechanisms of the ventral stream, the global motion mechanisms in extrastriate dorsal-stream areas are differentially vulnerable to neurological insults, likely to involve cerebral white matter, associated with preterm birth. Further analysis will relate these global processing measures to indicators from brain MRI in the neonatal period. We will also discuss the relation of these results to ‘dorsal stream vulnerability’ found in preterms and other neurologically compromised children in later childhood. (e.g. Williams syndrome, autism, fragile-X, hemiplegia; Braddick et al, Neuropsychologia, 2003).