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Our recent work has concerned examining the properties and role of spontaneous neural activity in the development of the visual system. Early brain activity is instrumental in the development and refinement of visual system connectivity. It was known since the early 1990s that the isolated retina in vitro, can display fantastic patterns of spontaneous activity ('retinal waves') during development. Retinal waves have been thought to mediate interactions at developing synapses through the information carried in their spike patterns, in effect 'wiring together' visual circuits and preparing the brain for vision based learning and behavior later in development. However it had remained unclear what the nature of retinal waves were in the living brain and whether circuits throughout the visual system exhibit similar patterns of activity.

Our research involved the first direct optical recordings of the developmental activity pattern known as 'retinal waves' in live mice via presynaptic calcium imaging from retinal ganglion cell terminals[1]. The work not only demonstrated that retinal waves do exist in vivo, but also through postsynaptic calcium imaging showed that waves propagate to and activate neurons throughout developing midbrain and visual cortex. Surprisingly, retinal waves have unique spatiotemporal properties (e.g. directionality and nucleation site preferences in binocular retina) that could not have been anticipated from previous in vitro recordings. Furthermore, retinal waves play a differential role in activating primary versus extrastriate visual cortical areas.

Figure 1. Imaging spontaneous activity throughout the developing visual system. a, Calcium imaging in GCaMP transgenic mice. Montage shows dF/F signals simultaneously in superior colliculus and ipsilateral visual cortex during a single retinal wave propagating in a resting neonate. b, Maps of retinotopy in superior colliculus and visual cortex based on spontaneous retinal wave-front position. c, Retinal wave propagation is matched retinotopically in superior colliculus and primary visual cortex.

Thus retinal waves provide a source of patterned information suitable for activity-dependent development in visual circuits before the onset of sensory experience and exhibit spatiotemporal properties that enable waves to match visual map development in visual cortex to the superior colliculus as well as coordinate inter-hemispheric circuit refinement. This work significantly advances our understanding about the origin and nature of neural activity that is likely present for a substantial period of human gestation and which sculpts wiring throughout the developing brain[2].

Previous research

  1. Ackman, J. B., Burbridge, T. J., and Crair, M. C. (2012). Retinal waves coordinate patterned activity throughout the developing visual system, Nature, 490(7419), 219-25 ↩︎

  2. Ackman, J. B. and Crair, M. C. (2014). Role of emergent neural activity in visual map development, Curr Opin Neurobiol, 24C(), 166-175 ↩︎