So periodically I fulminate against the notion of the brain’s hard wiring like in my post last year on the movie Transcendence or just a few weeks ago about variant views of empathy. In the effort to be more balanced I want to discuss more about the chemical side of the MEMBRAIN. I have been thinking as I have read various things, especially Joseph’s Neuroscience text, about cephalization, the evolutionary trend in which neuronal structures and processes increasingly congregate in the head, i.e., into a brain. I once had a ‘discussion’ with a friend who insisted that if you pushed a knife through a lobster’s shell just behind the eyes, it would feel no pain once thrown into the pot because the brain would be severed from the spinal cord. It mattered little to him that lobsters do not have a brain and spinal cord but lines of ganglia. They do have a head ganglion that is larger in order to process visual information and coordinate movements to gather in food or grab objects with their claws but otherwise the ganglia operate relatively independently. I suspect they do feel some version of pain maybe in one ganglion or several when confronted with aversive stimuli such as high temperature or another lobster clipping a leg or claw off, but I know it is not pain as a centralized emotion such we ‘cephalized’ creatures feel. Sharks were in at the beginning of the cephalization movement some 420 million years ago.
With cephalization comes a more complicated MEMBRAIN and a greater interiority, i.e., the mind within the MEMBRAIN greater on the inside than outside. The MEMBRAIN functions, then, of passing information in and out and keeping information in and out, correspondingly grow more complicated. Yes, the neurons, dendrites and axons are organized wire-like into different systems or circuits, and intra-neuron communication is via evoked potentials, thus we can measure the electrical activity of the brain, e.g., EEGs. However, inter-neuron communication is via chemicals, i.e., neurotransmitters, and there are many and they are important to way the MEMBRAIN works.
For one example, take passing information in through various channels. Different circuits in the perceptual system operate with different neurotransmitters as I learned from Panksepp and Joseph. Parallel processing using these different neurotransmitters works to select and sharpen different percepts and inhibit others. For example, per Panksepp, norepinephrine helps to elevate a particular signal over the surrounding noise, acetylcholine promotes arousal and attention to sensory channels, and serotonin modulates input to keep sensory information clear as it is integrated across modalities. Then we have dopamine that mediates motivation and stimulus valence.
Likewise, per Joseph, on the output side, the same neurotransmitters as on the sensory side organize and carry out motor commands to muscles but other neurotransmitters, GABA and glutamate, modulate the signals outward bound so that muscle contractions are graded and coordinated. Also on the output side dopamine is important in maintaining clarity of signal and inhibition of unintended movements. For example, in Parkinson’s disease, low dopamine translates into unwanted tremors that interfere with intentional actions.
All so complicated and I have not gone into my usual riff on hormonal influences, such as oxytocin on social caring behaviors. We have much to learn on many levels here and I find that exciting. I hope you now understand why I react so to the overuse of the “hard wired” metaphor for our brains, and why I propose we call computer circuits “dried neurons”. Travel on.