.
\nSensory experience changes the way humans see the world
\nduring early postnatal development. Now, an international team
\nof researchers, including Tadaharu Tsumoto from the RIKEN
\nBrain Science Institute in Wako, may have an explanation. They
\nreport in the journal Neuron that visual experience drives the
\nmaturation of inhibitory synapses in the visual cortex during a critica
\nl period of early postnatal development by activating endocannabinoid
\n receptors1. \u201cThis maturation makes synaptic transmission more
\n reliable,\u201d explains Tsumoto. These findings may be crucial to
\n understanding the changes in the way the brain processes
\nvisual information from early postnatal life to puberty.
\n.
\nThe researchers electrically stimulated the visual cortex and
\nmeasured the resulting inhibitory currents in the superficial layer
\n of visual cortex slices from 3-week-old rats, a time during development
\n soon after the initial opening of the eyes. High-frequency
\nstimulation of the slices\u2014similar to input that visual cortex neurons
\n may receive during visual experience\u2014led to a long-lasting drop
\n in the amount of inhibitory current that the stimulation could elicit.
\nThis is called long-term depression of inhibitory currents (iLTD).
\nTsumoto and colleagues could not induce iLTD in the visual cortex
\nof 5-week-old rats, a stage in development akin to puberty. The
\n researchers therefore realized that there was a \u2018critical period\u2019
\n for the induction of visual cortex iLTD that occurred after eye opening.
\n.
\nInterestingly, Tsumoto and colleagues were able to delay the onset of the
\ncritical period by raising the rats in darkness, and even brief exposure
\nof dark-reared rats to light induced the loss of iLTD in the visual cortex.
\nThe research team realized that visual experience therefore plays an
\nimportant role in regulating the timing of the critical period.
\nEndocannabinoids are signaling molecules that regulate neuronal
\nactivity throughout the nervous system. The researchers showed
\nthat a drug that activates endocannabinoid receptors can induce the
\n loss of iLTD in the visual cortex in dark-reared animals that would
\nnormally still exhibit iLTD, while a drug that blocks endocannabinoid
\nsignaling could inhibit the loss of iLTD that is normally induced by
\nlight. This suggested to Tsumoto and colleagues that visual experience
\n drives endocannabinoid signaling to induce iLTD during visual
\ncortex development.
\n.
\nThe researchers argue that endocannabinoid-mediated iLTD seems
\n to be important for the maturation of inhibitory synapses that occurs
\nduring development of the visual cortex. Tsumoto suggests that this
\nmaturation could help to \u201cmake responses of neurons in the visual
\n cortex selective to a particular feature of visual stimuli,\u201d such as
\norientation of contours or direction of movement.<\/p>\n","protected":false},"excerpt":{"rendered":"
. Sensory experience changes the way humans see the world during early postnatal development. Now, an international team of researchers, including Tadaharu Tsumoto from the RIKEN Brain Science Institute in Wako, may have an explanation. They report in the journal Neuron that visual experience drives the maturation of inhibitory synapses in the visual cortex during … <\/p>\n