Scientists are a step closer to unravelling the mystery of sight now that they have revealed part of the process by which the brains of mice interpret visual stimuli.
From previous research, scientists understood that neurons in the visual cortex – the part of the brain that processes sensory impulses from the eyes – exchange excitatory signals through connections called synapses according to the distinct features in a visual space.
Despite this, the exact connectional logic behind this network remained a mystery as it was unclear what information these individual neurons receive from a visual field and how this impacts the visual features that each cell encodes.
The new research, conducted by Maria Iacaruso from the University of Oxford and her colleagues and published in Nature, endeavoured to explore this process by mapping the interactions between individual neurons in the visual cortexes of mice as the animals reacted to black and white squares placed in different parts of their field of view.
To map this synaptic activity, the researchers measured brief increases in calcium-ion concentration, which occur in response to the activation of neuronal dendrites – extensions of neurons through which electrical impulses travel to move between cells.
From their study, Iacaruso’s team found that the synaptic activity in the mice tended to mirror the organisation of the visual space around them, particularly with respect to edges and lines.
Iacaruso and her colleagues note that this not only holds true for the signals coming from the particular part of the visual field involved but also for supplementary signals that come from more distant sections of the field of vision.
These signals are delivered to a particular neuron according to its predilection for spatial orientation, which helps provide context for the primary signal, as Iacaruso’s colleague Sonja Hofer explains.
“Our visual environment contains many long lines and contours,” Hofer says. “The structure of the world around us is therefore mirrored in the pattern of synapses in the brain.”
Hofer claims that the brains of mammals are so good at identifying contours and objects in images that they are occasionally deceived into seeing them when they do not exist, such as in optical illusions.
The work of Iacaruso, Hofer and the rest of their team is an essential step in the investigation of the relationship between synaptic activity in mammalian brains and the vision it helps create.
Angus Bezzina is a writer from Sydney, Australia.
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