Cortical spontaneous activity at birth in a control mouse (left) and a mouse where retinal waves were blocked by carbenoxolone injection into the eye (right). Credit: Instituto de Neurociencias (IN, CSIC-UMH)
Key Points:
- A study published by Spanish scientists reveals that the senses of sight and touch are separated by the brain only after birth.
- The research team studied the brains of mice to reach this conclusion, and found the separation to take place in the superior colliculus.
- Impeding the superior colliculus from splitting the two senses was found to cause sensory issues.
Scientists in Spain spearheaded a study that sheds light on sensory development at the embryonic stage. The study, published in Science, determined that the neural pathways responsible for touch and sight are interdependent before birth. The neurons are restructured after birth, and it is only at that point that the brain perceives the two senses separately.
The scientists discovered in a mouse model that the division of touch and sight is achieved in the superior colliculus, a part of the brain that assimilates sensory information and translates it into a motor response by the body.
The team knew beforehand that the sensory neural pathways were activated by tactile stimuli. What was not known, however, was whether they were activated independently or if a certain degree of enmeshment existed. Experiments on the embryonic brains of mice led the scientists to conclude that tactile stimuli simultaneously activated cortexes of the brain responsible for both touch and sight.
"We then tested whether the disappearance of this multimodal response could be related to the arrival of signals from the retina to the cerebral cortex and other brain structures,” said Teresa Guillamón-Vivancos, the lead researcher. “Our data show that somatosensory and visual circuits are not secreted by default, but require the arrival of activity waves from the retina to do so.”
Guillamón-Vivancos’s team discovered that the separation occurs close to birth when activity from the retina signals the superior colliculus to divide the pathways. Consequently, the scientists learned that preventing the retina from signaling the superior colliculus caused defects in how the brain processes tactile and visual stimuli.
The scientists say they will continue studying the development of evolutionarily significant body parts to better understand how different parts of the brain form.