Corpus callosum🧠
The corpus callosum is the part of the brain which connects the left and right hemispheres. It contains an estimated 300–800 million fibers connecting topologically similar areas in either hemisphere. Yet only 2 per cent of cortical neurons are connected by this tract. What is more, the main purpose of a large number of these connections is actually to inhibit—in other words to stop the other hemisphere interfering. Although the majority of cells projecting to the corpus callosum use the facilitatory neurotransmitter glutamate, and are excitatory, there are significant populations of neurons that use the neurotransmitter GABA whose function is inhibitory. The evidence is that the primary effect of callosal transmission is to produce functional inhibition.
So much is this the case that a number of neuroscientists have proposed that the whole point of the corpus callosum is to allow one hemisphere to inhibit the other. Stimulation of neurons in one hemisphere commonly results in an initial brief excitatory response, followed by a prolonged inhibitory arousal in the other, contralateral, hemisphere. Such inhibition can be widespread, and can be seen on imaging. Even the excitatory fibers often terminate on intermediary neurons, or ‘interneurons’, whose function is inhibitory. The types of attention that the cerebral hemispheres bear to the world are incompatible, thus the corpus callosum keeps them from interfering with each other.
References
- Mcgilchrist, Iain. (2010). The Master and His Emissary Chapter 1 Asymmetry and the Brain (p. 41). London, UK: Yale University Press.
Metadata
Type:🔵 Tags: Biology / Neuroscience / Anatomy / Neuroanatomy Status:☀️