This is part two of a two-part series. Find part one, here.
The Neurology of the Aggregates
What follows is a summary of the neurology that is associated with the psychology of the Aggregates. In other words, these are the structures and functions of your brain that enable, underlie, and are in a sense, one with the movements of your mind.
You don’t really need to learn or remember any of the details that follow (unless you want to). The point is to get a feeling for the incredible compounded complexity that produces the moment to moment unfolding of lived experience. A great way to do this is to pause periodically as you read and imagine the physical processes that are producing your sensing, feeling, perceiving, thinking, and awareness.
Neuroanatomy of Form and Sensation (The First Aggregate)
The term, “sensation,” can refer both to the most elemental experience of the physical world (that’s its meaning in the Buddha’s system of the Five Aggregates), and to one of the five basic senses, the tactile one. Just keep this in mind when we get tactile sensing below.
- Basic anatomy – Rods and cones to ganglion cells in retina, then optic nerves to lateral geniculate in brainstem, then optic radiations to occipital cortex in back of head. The left visual field goes to the right occipital region, and vice versa; events below the horizon go to the upper occipital areas; in other words, your brain receives a doubly mirrored set of inputs which it unscrambles to let you hit a baseball or drive a car.
- Basic physiology – One-hundred million rods detect dim light, five million cones detect daylight vision and color (three types of cones, for short, middle, and long wavelengths of light). Ganglion cells organize the output into receptive fields. The lateral geniculate organizes the visual data into fine grain color vision (red-green, blue-yellow) and a sense of luminosity.
The data input stream consists of about 10 million bits-per-second of visual information; the cortex processes this data and filters out a lot of it. Even with all that filtering, your brain receives around 5 to 50 “pictures,” each second.
From the primary visual cortex, two pathways emerge—a vision-for-action path to parietal and then to frontal lobes, and a vision-for-perception path to temporal and then to frontal lobes. Visual consciousness occurs in the path through the temporal lobes, where memory and identification happen.
- Fun facts – The central one degree of vision is heavily overrepresented with processing power in the brain – kind of like the zoom center of a movie camera – so we move our eyes around a lot to take advantage of this high-power center of the visual field.