Spatial and temporal properties of visual responses in the thalamus of the developing ferret.

Spatiotemporal patterning of neural activity is thought to influence the development of connections in the visual pathway. This patterning can arise spontaneously or through sensory experience. Here, we use a combination of natural and simple stimuli to investigate which elements of the visual environment modulate the earliest responses in the primary visual pathway of developing ferrets. Recordings were made during the first 2 weeks of visual responsiveness, which, in the ferret, overlaps with the period that the eyelids have not yet opened. Even when the eyelids are closed, both thalamic and cortical activity was found to be temporally modulated under conditions of natural visual stimulation. The modulations correlated with temporal changes in stimulus contrast but also reflected spatial structure in the visual scene. Simple stimuli were used to show that early responses to naturalistic stimuli are influenced by the localization and structure of through-the-eyelid receptive fields. The early visual responses were also characterized by substantial variability in the ability of the cells to detect stimuli of different duration and different intensity, in a temporally precise manner. These temporal and spatial properties should constrain how plasticity mechanisms interpret naturally patterned activity.