Ar. Pearce et al., Development of functional connections between thalamic fibres and the visual cortex of the wallaby revealed by current source density analysis in vivo, J COMP NEUR, 418(4), 2000, pp. 441-456
Functional development of thalamic input to the cortex in anaesthetised wal
laby pouch young between postnatal day 25 (P25) and P153 has been studied b
y electrical stimulation of the optic nerve, current source density (CSD) a
nalysis, and histologic identification of recording sites. Conduction in th
e optic nerve was recorded prior to P39, by which time responses from the s
uperior colliculus appeared. No evoked potential of cortical origin was rec
orded until P46, even though thalamic fibres grew into the cortical plate f
rom P15. The first cortical synaptic responses were recorded at the margin
of the subplate and the developing cortical plate, where cells that later c
omprise the adult layer 6 settle. At about P66, an additional short-latency
, superficial response appeared, coinciding with the formation of layer 4.
The deep response was retained in layer 6. Evoked activity in the presumed
layer 4 was found progressively deeper in the cortex over the next few week
s, which would be expected from the addition of layer 3 above it. By P113,
a new sink was added superficial in the cortex. Thalamocortical connections
follow the same deep-to-superficial order in development as the cellular l
ayers of the cortex. (C) 2000 Wiley-Liss, Inc.