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.
Vision
- 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.
The brain paints in the blind spot by inferring from neighboring inputs.Vision fades when you focus on one spot. Vision is suppressed during eye movements – one reason why your video of your kids playing around in the yard is so jerky, as an example.
Hearing
- Basic anatomy and physiology – Hair cells in cochlea increase their firing rate as they are squeezed between the basilar membrane and the tectorial membrane. The cochlea is tonotopically organized. Some of the localization of sound in space starts in the brainstem, in the superior olivary complex, which establishes the time delay between sound arriving at left or right ear. Starting at the brainstem, the auditory pathway goes through a series of nuclei—the dorsal and ventral cochlear, the superior olivary, the lateral lemniscus, the inferior colliculus, the medial geniculate. Multiple cross-connections occur at each level. The bulk of neural activity from one ear winds up in the contralateral temporal lobe.
- Fun facts— Sounds can blend into each other and be misidentified.
- Cocktail party phenomenon—you can track one person’s voice in a complex auditory environment.
Speech and prosody (the musical quality of speech) are different neurological functions, and are actually located on different sides of the brain.
Smell
- Basic anatomy and physiology—100 million olfactory afferent fibers travel into your olfactory bulbs (you have two of these). These bulbs are organized into glomeruli (25000 receptor inputs), which respond to physicochemical properties of the odorant molecules. Local circuits and feedback inhibition result in mitral cell outputs that correspond to subjective sensations. Mitral and tufted cells project to central structures, including the amygdala, the cortex near the hippocampus, and the hypothalamus.
- Fun facts—Pheromones cause menstrual cycle synchronization.
- Most of taste is odors.
Notice how your olfactory memories are so strongly encoded.
Taste
- Basic anatomy and physiology—Taste buds detect four sensations—sweet, sour, salt, and bitter. The tip of the tongue detects all four, the anterior sides of the tongue detect sour, and the back of the tongue detects bitter. The sensory inputs come in on three separate cranial nerves, but integrate in the nucleus of the solitary tract. From there, the information is relayed to a pontine taste area, which projects to the lateral hypothalamic area, the amygdala, and the thalamus. From the thalamus, the sensory cortex near the face area is informed.
- Fun facts—Taste reflex arcs (circuits) in the brainstem cause both salivation and “gustatory sweating.”
- Taste is represented bilaterally, so it’s hard to know which side of the tongue is stimulated (try this sometime).
Tactile
- Overview – There are two types of tactile sensing: somatic and proprioceptive.
- Somatic, basic anatomy—Cutaneous receptors come in six types:
Four mechano-receptors
- Fast adapting – Pacinian corpuscle
- Slow adapting – Merkel’s disc
- Hair follicle endings – quickly adapting
- Meissner’s corpuscles – serving sense of touch
Two thermo-receptors
- Krause’s endbulb – free nerve endings
- Pain – free nerve endings
Proprioceptive (position):
- Joints – four receptor types giving movement, position, and pain
- Muscle – four receptors: one for vibration, one for pain, a Golgi tendon organ to detect tension, and a muscle spindle organ to set the length of the muscle.
- Incoming sensation from the body and the face is divided into two major systems:
- a posterior column system carrying discriminative touch or pressure, muscle length and tension, and joint position and vibration, all focused on mediating fine tactile and kinesthetic sensations.
- an anterolateral system carrying information about pain, temperature, coarse touch and pressure.
These systems relay in the thalamus and are passed on to cortex.
There are slight differences in the locations of the pathways in the brainstem and the relay stations in the thalami, but the principles are the same. The incoming sensory pathways are also under continuous dynamic control, both locally and from the cortex-thalamus-brainstem— an example is pain suppression.
- Fun facts— Your brain routinely suppresses pain signals so that you can pay attention to other things; it’s only when the pain signals get intense that they break through into awareness.
Note that the sensation from any part of the body is broken up into so many different characteristics that it isn’t a unitary experience at all. The cortex makes up that fable for convenience.
Visceral
This is a kind of sixth sense (not a paranormal one) that is commonly lumped together with the tactile sense.
This class of sensation is largely mediated through the autonomic nervous system, which regulates our internal housekeeping department.
Neuroanatomy of Feeling (The Second Aggregate)
Recall that “feeling” here does not mean emotion, but the basic tone of an experience as pleasant, unpleasant, or neutral.
The primary neurological unit in your brain that creates the feeling tone is the amygdala, with a supporting role for the hippocampus and the insula.
The “decision” the amygdala makes for labeling an experience is heavily influenced by “upstream” processing in the nervous system, especially related to pain and pleasure.
Pain –starts locally, the product of a stimulus suggesting actual or impending tissue damage. This activates nociceptive fibers (both myelinated fibers that cause the jerking away response and “electric” sensation, and unmyelinated fibers that are slower and mediate the burning/aching sensation), which travel to the spinal cord or brainstem and are then relayed to thalamus and cortex. This results in the activation of behaviors such as withdrawal, wincing, or changes in facial expression.
As pain signals cascade through neural circuits, the autonomic nervous system is activated, especially the sympathetic systems, which participate in regulating the organism’s response to actual or threatened damage. The heart rate and blood circulation alter. Chemical signals from damaged tissues result in white cells migrating to the area, and these chemicals also stimulate pain neurons. All this is at a very fundamental level in your body.
Pain is also a feature of higher cortical functions, such as loss, embarrassment, frustration, and other mismatches between desires and attainments. There is a feedforward mechanism between pain thresholds and depression such that pain sensations are perceived more intensely by depressed people, and those amplified pains contribute to the maintenance of the depression.
Pleasure -Much more complicated. It’s actually not the opposite of pain, but rather a different direction. It has more to do with the relief of a perceived imbalance, such as hunger or thirst or sexual/sensual gratification. A lot of these behaviors are coordinated at the hypothalamic and limbic system level. At a higher cortical level, the forethought of how not to have a problem, the anticipation of reward, is pleasurable. The opening up to the experience leads us to seek and approach and attain.
Neutral (boredom)—Some might argue that no truly neutral experience actually exists, but the sensations coming in are below the threshold of necessary avoidance or the cost of pursuit. The thrust of a living organism moving through time is to seek pleasure and avoid pain: who cares about the neutral?! Subthreshold stimuli probably initiate a search mechanism to find the next great thing.
Therefore, as a meditation practice, these neutral stimuli are useful to help us note why we keep chasing rainbows or running from ghosts. And in the addiction world, the experiences of cocaine, methamphetamine, and crack addicts shows how the modification of the dopamine receptor by stimulant exposure diminishes enjoyment responses to everyday sensations, therefore making them unsatisfying, which increases the search for more intense pleasures (e.g., the next fix).
Neuroanatomy of Perception (The Third Aggregate)
Out of the sensory inputs, neural patterns related to the object are constructed in the appropriate cortices, involving many different regions working in concert and synchronized by the 40 Hz gamma oscillation frequency of the cortical columns involved.
The various aspects of the object are mapped. These mappings are simultaneously compared against memories of previous experiences. A perception is born. It is categorized as a concept or language or experience, and stored for later retrieval and comparison. Sometimes you can observe this coding in action.
Examples: Visual of forms, letters—Try not to see the letter “W.” Try not to see the color of your skin. Auditory of sound—On a retreat once, the buzzing of a fly in my (Rick Mendius) ear morphed (as the fly moved away) imperceptibly into the train horn down in the valley. Smell and memory—Diesel exhaust on a cloudy wet day evokes Vienna for me.
Neuroanatomy of Mental Formations (The Fourth Aggregate)
This is where it gets interesting.
The emotional, volitional, and intellectual aspects of any experience can now be seen as a result of the combination of:
- the genetic loading of the organism at conception
- the biological progress of that nervous system and body through embryogenesis and development up until this moment
- the experientially determined behaviors and memories of that organism
All of this biases the organism to perceive and react to stimuli – including internal stimuli – in a particular way, whether it’s the banana on the table or the PTSD experience of loud noises imitating Iraqi IEDs.
Each experience has a resonance throughout the entire brain, from multiple sensory systems to memory stores to preferential motor responses. These resonances are mediated by coalitions of cortical columns throughout the brain, coupled with their cortical connections and brainstem-hypothalamic-spinal cord-somatic-autonomic connections.
For example, the neurologic correlate of visual conscious awareness is a 40 Hz oscillation synchrony.
There is a habitual pattern of interaction, which has proven effective in the past, which will predominate the oscillations because “neurons that have fired together have wired together and will fire together again.” Because this is a dynamic and inherently unstable system, there is hope that the organism can correctly perceive this unique moment and act effectively.
Most of the time, that is what happens.
But, we need to work our brains to correct the times that this does not. This is the everyday process of learning from experience; as they say in medicine: “Good judgment comes from experience . . . and experience comes from bad judgment.” And it is also the not-so-common process of serious introspection, deliberate psychological growth, and spiritual practice.
Neuroanatomy of Consciousness (The Fifth Aggregate)
While the term, consciousness, is routinely used, it has many philosophical and religious associations that go far beyond its meaning in a neurological or psychological sense. Probably the word, awareness, is better since it is simple and clear (relatively speaking!). That’s what we mean here when we speak of “consciousness.”
With that preamble out of the way, it’s worth noting that most neurological activities never rise to the level of awareness. Nonetheless, these processes within processes within processes usually are – taken as a whole – incredibly intelligent.
For example, I (Rick Hanson) was once rock climbing in Colorado and standing on a tiny belay ledge overlooking a river 500 feet below. As I paid out the rope for my friend climbing above, and reflected on all the high tech gear and training that enabled us to progress safely up territory many would consider insane, I saw a large black ant crawling up the coarse granite in front of my nose. It reached its claws and legs up and over crystals in the rock that, at its scale, amounted to much more difficult ground than my friend and I could handle. That ant was a heck of climber! Then it occurred to me that with all of modern science and computer technology, humans are still not able to make a robot that could do what that ant could, with a brain smaller than a grain of sand.
And that was simply an ant. Just imagine all of the activities occurring beneath conscious awareness that get assembled in increasingly complex and summary architectures of meaning until they just barely break the waterline of consciousness, the tiniest discernible tip of a vast iceberg below.
To be sure, many of these activities involve relatively simple circuits, sometimes so simple that they’re called “reflexive.” Perhaps a better term for behaviors that do not require conscious awareness and direction, but which rely upon adaptive and learned patterns of neurological activity, is “automatic.” Christof Koch and Francis Crick sometimes refer to these as “zombie” activities, which is evocative, but which might lead one to underestimate the sophisticated information processing they require – even if it’s only a “soulless one” lurching down Main Street in a B movie.
An excellent discussion of the possible neurology of consciousness – a subject that is still in its scientific infancy, and full of controversy – can be found in Antonio D’Amasio’s book, The Feeling of What Happens. In particular, he makes a crucial distinction between “core consciousness” and “autobiographical consciousness.”
Core consciousness, in D’Amasio’s terms, is the appearance of an external stimulus or internal state at the point of awareness. It is right after that appearance that we can gain some control over the process, and change our behavior.
When the autobiographical consciousness begins to take hold, we can rewrite the chapter of the book. That is dependent on practicing with the internal witness, whose anatomic correlate is probably the anterior cingulate. That appears to be one of the main points of meditation practice, to use the recursive watcher of the watcher circuitry, which is built into the system, to familiarize ourselves with how we construct this moment. Knowing how something is built up gives us the perspective and the tools to deconstruct it, refurbish it, and improve it.
In Sum
- There are recurring themes in neuropsychology – and contemplative practice –
of differentiation and integration. - There is mindfulness of the body, to be sure. But also a body of mindfulness, or
embodied mindfulness. - In other words, the mechanisms that produce mindfulness of the body are
themselves embodied! It is the body being mindful of the body.
May you be ever more mindful of your body. And bodily mindful!
This article is Part Two of a series: Part One – The Five Aggregates
© Rick Hanson, PhD
