Babies see blurry images during their first few months—their eyesight comes online only later. A new study published in Nature Neuroscience provides further insight into the workings behind this miracle of life.
From darknesses to light—such is the transition from womb to birth. Then, the eyes of the newborn have to get acquainted with the drastically-different world into which he finds himself. So, a baby opening his eyes for the first time will not see well at all; rather, he will be greeted with images of blurry objects dancing in the light and the dark. Thereafter, his eyesight will adjust itself, and the next level will be recognition: this will happen gradually, as he will first recognise people, and then, few months later, objects in the background—everything is now properly focused.
As these processes unravel, changes in the brain are simultaneously happening, thereby accounting for the gradual focusing. The team of researchers behind the recent findings aimed at understanding this very brain wiring. Led by Spencer Smith, assistant professor of cell biology and physiology, the scientists looked into the functioning of the brain areas involved in bringing about vision in its earliest stages, that is, at birth. Smith summarises the unwinding of the processes as follows:-
“There’s this remarkable biological operation that plays out during development,” Smith said. “Early on, there are genetic programs and chemical pathways that position cells in the brain and help wire up a ‘rough draft’ of the circuitry. Later, after birth, this circuitry is actively sculpted by visual experience: simply looking around our world helps developing brains wire up the most sophisticated visual processing circuitry the world has ever known. Even the best supercomputers and our latest algorithms still can’t compete with the visual processing abilities of humans and animals. We want to know how neural circuitry does this.”
Smith investigated two subnetworks making up the visual circuitry, namely the ventral and dorsal streams, the aim being whether visual experience is important for the latter’s development. The team, therefore, reverse-engineered the brain circuitry with specialized two-photon imaging systems in order to get to the functioning of the networks. Using this technology with the objective of investigating specific brain regions with neuron-level resolution, mice were reared in complete darkness, and compared with normal ones. The probing show that the ventral visual stream comes online immediately; the researchers even found individual neurones firing when the mice would respond to visual cues. On the other hand, the dorsal stream remains offline, so to speak, for some time. Neurones located in the dorsal area were not firing as fiercely as those in normal mice.
“Keeping the mice in darkness significantly degraded the magnitude of visual responses in the dorsal stream – responses to what they were seeing,” Smith said. “Interestingly, even after a recovery period in a normal light-dark cycle, the visual deficit in the dorsal stream persisted.”
This effect is actually similar to what humans with bilateral cataracts experience; fully understanding the visual brain circuitry and the functions of the relevant brain regions is crucial to treating partial or complete blindness.
“Not only did the mice need visual experience to develop their dorsal stream of visual processing, but they needed it in an early developmental time window to refine the brain circuitry,” Smith said. “Otherwise, their vision never properly developed.”
Interpreting the findings further, the researchers explain that human newborns might be going through similar changes in their ventral and dorsal streams. What the mice went through might be analogous to what happens to us as our vision is slowly unravelling during our first few months in this world.