The brain re-constructs the hologram.

And with the same amount of power as a clock radio, it does this quite efficiently.

Brain Stem

Continuing up the central nervous system, we are arrive at the brain stem which connects the spinal cord to the thalamus.

It’s how the body plugs into the brain for data processing and feedback control.

In addition to connecting the body with the mind, the brain stem is also responsible for regulating several autonomous functions, controlling basics such as heart rate, blood pressure, breathing, swallowing, and alertness.

A virtual spinal cord and brain stem

As such, it is said to be pivotal in maintaining consciousness.

Cerebellum

Hanging off the back of the brainstem is the cerebellum, which is a rather intriguing structure.

Receiving inputs from the spinal cord and other parts of the brain, its main function seems to be precision motor control, which encompasses a wide range of activities, including articulations of the thumb and motions of the mandible.

And while the cerebellum does not initiate movement, it contributes largely to the coordination, precision, and accurate timing of it. As such, it’s also responsible for motor learning, adapting and fine-tuning its motor programs through a process of trial-and-error.

But what’s really interesting is it’s structure.

The cerebellum’s function is best understood not in terms of the behaviors it affects, but the neural computations it performs; the cerebellum consists of a large number of more or less independent modules, all with the same geometrically regular internal structure, and therefore all, it is presumed, performing the same computation.

In other words, the subtleties and nuance of motion are computed independently and on a generic system-wide architecture.

Additionally, the cerebellum is a one-way street. Input comes in from the spinal cord and other brain regions, gets refined, and the output goes right back out to motor control.

As the nervous system requires a quick and clear response to the input, the cerebellum, with its feed-foward design, is thus able to drastically reduce noise by eliminating the possibility of feedback created by recurrent neural connections.

And for a real-time biological computer, this a great performance advantage.

Studies have shown that the cerebellum is activated during language, attention, and mental imagery tasks as well. Pressing inward, “what the cerebellum is doing to movement, it’s also doing to intellect and personality and emotional processing.” [link]

The cerebellum, then, is the center of balance and refinement. Precision steering for the body and mind.

What one might call our reptilian brain.

Cerebrum

Diencephalon

At the end of the body’s information super highway is a region called the diencephalon, which literally means between-brain.

As such, it’s the relay station of sensory and motor data between the body and the brain.

The hypothalamus connects the nervous system to the endocrine system, and the pituitary gland is basically a hormone factory under its control, regulating metabolism, growth, reproduction, sleep, mood, etc.

The thalamus is the integration hub and relay station of sensory and motor data.

It pre-processes data by transforming and integrating it, and then sends it along to the appropriate cortical regions for further computation.

The thalamus, then, is the gatekeeper to cognition. With help from the pineal gland, it also regulates states of sleep and waking consciousness.

One way to think about the thalamus is through the lens of reality modulation and gain control. It’s a bottleneck through which data about perception and movement must travel, a low-pass filter necessary for attention and focus.

The Limbic System

As data is passed between thalamus and the neocortex for cognition, it also travels through the limbic system, whose main functions are motivation, emotion, learning, and memory.

It performs lower order emotional processing of input from the sensory systems, and it is the seat of our emotional lives.

Amygdala

The amygdala’s primary function is the processing of memory, decision-making and emotional responses — including fear, anxiety, and aggression. More emotionally arousing stimuli increase the amygdala’s activity, and the level of this activity is correlated with memory retention.

Hippocampus

The hippocampus is primarily responsible for memory consolidation, transferring content from short-term and working memory to long-term storage. It also serves the function of spatial memory which prevents us from getting lost — most of the time.

As a whole, the limbic system provides an emotional reinforcement learning algorithm for the simulation. It’s a mental map of the world with a feedback loop for our actions, mediated as they are by feelings, thereby coloring the memories we store and retrieve.

A vehicle for re-membering the hologram and navigating our way through it.

Emotion is the key to its ignition.

Neocortex

At last we have reached the end of the road for the central nervous system, a region of the brain otherwise known as the neocortex, or the seat of rational thought.

As the most recent addition to our evolutionary arsenal in the pursuit of intelligence, it’s responsible for higher-order brain functions — which include “sensory perception, cognition, generation of motor commands, spatial reasoning, and language.”

With its deep grooves and ridges, the folding of the neocortex drastically increases the surface area available for processing which, more or less, explains the rise of humanity.

A convoluted hyperbolic manifold.

And consisting of columns with several layers, the neocortex distributes the parallel processing of perception, thought, and action into separate modules called lobes, each responsible for a particular dimension of experience.

There are 4 lobes of the brain and they are occipital, temporal, parietal, and frontal.

Occipital Lobe

The occipital lobe is the visual processing center of the brain. It deconstructs the visual signal of the world into parts and projects it through the lens of focus and attention.

It creates our perception of 3-dimensional space.

Temporal Lobe

The temporal lobe is the region where sound, language, and speech comprehension are processed.

In short, it is the timekeeper of the brain.

Parietal Lobe

The parietal lobe plays an important role in the integration of sensory information from the body, with the knowledge of numbers and their relations, and in the manipulation of objects.

It is the primary area of body and spatial awareness, and, in addition to the temporal lobe, holds the power of association.

Somatosensory Cortex

The somatosensory cortex is a region of the parietal lobe that receives and processes sensory input from the entire body.

The sense of touch. Input.

Comparison of cortical surface area mappings for somatosensory and motor cortex

Motor Cortex

And the motor cortex, a portion of the frontal lobe, manages the planning, control, and execution of voluntary movements.

The seat of action. Output

Frontal Lobe

The frontal lobe is the part of the brain that controls important cognitive skills such as “emotional expression, problem solving, memory, language, judgment, and sexual behaviors.”

Inside Out

It is the control panel to personality and our ability to communicate.

The orchestrator of thought and action in accordance with internal goals, the frontal lobe is often considered the seat of self-awareness.

Cortical Layers

With the dimensions of experience computed in parallel across the lobes, how then, do they actually compute?

In order to efficiently make sense of the world and act on it, the neurons in the neocortex evolved into 6 distinct layers, providing recurrent connections and feedback loops for data passing through the cortical columns.

The 6 layers of the neocortex

With a collection of layered neurons, we have a computational grid for performing integration and differentiation of inputs, having either excitatory or inhibitory effects on their neighbors, and producing a rather complicated neural network.

Entangled strings of neurons, if you will.

And each layer consists of a characteristic distribution of neurons and connections to other cortical and sub-cortical regions, including thalamus.

In the simplest caricature, input comes in on layer 4, is passed to layers 2/3 for processing, and feeds to layer 5 for output to thalamus.

Additionally, layers 2/3 feed to layer 1 which also projects axons to layer 6.

Layer 6 is feedback control. It connects directly to thalamus, and influences input on layer 4 and output on layer 5.

With the recurrent connections and feedback loops of cortical laminae, we are provided the architecture of thought.

Neurons

As noted, each of the lobes of the brain consists of columns of nerve cells distributed in layers and these specialized nerve calls are neurons. They are the fundamental computational units of the brain, and when considered individually, they perform a very simple function.

A neuron with dendrites (upper left), a soma (nucleus), and an axon (lower right)

A neuron consists of dendrites (input), the soma or cell body (computer), and one axon (output). And depending on the inputs, a neuron will either fire an action potential or not in response, essentially a bit. 1 or 0.

Grey Matter

Up to this point, we have been largely exploring white matter, the tracts of nerve fibers for signals to propagate through the nervous system and the neurons themselves. The wiring, as it were.

And the distinction with white matter is its myelinated axon sheath, or insulating cover, that allows for the transmission of signals across great distances. White matter also contains relatively few cell bodies, and is composed mostly of long-range axons.

In other words, a little bit of computation and a lot of output.

Grey matter, on the other hand, contains a large number of neuronal cell bodies but few axons.

That is, lots of computation, but little output.

Additionally, those axons are un-myelinated, meaning their influence is strictly local, and they are packed closely together.

Glial Cells

Glial cells are non-neuronal cells in the central nervous system, meaning they do not produce electrical impulses. Nonetheless, they play an important role in maintaining homeostasis by providing support and protection for the neurons.

Four different types of glial cells found in the central nervous system: ependymal cells (light pink), astrocytes (green), microglial cells (dark red), and oligodendrocytes (light blue). [link]

Additionally, glial cells are crucial to the function of neurotransmitters.

Grey matter and glial cells, taken together, are neural dark matter, the underlying bio-chemical grid supporting electrical oscillation in the brain, weakly interacting with the neurons of the white matter.

Claustrum

And one last piece to the puzzle is the claustrum.

The claustrum is a thin, bilateral surface that connects cortical regions to the thalamus.

It is the most densely connected structure in the brain allowing for integration of various cortical inputs (ex. colour, sound and touch) into one experience rather than singular events.

And due to its location deep inside the brain and with only a few cases of specific damage to this region to draw from, the study of the claustrum remains difficult.

Nonetheless, it is thought to play a key role in consciousness and sustained attention.

Ventricles

And sitting at the center of the brain, supplying it with nutrients and removing its toxins, are the ventricles. A dark space filled with cerebro-spinal fluid (CSF) that is critical to all brain functions.

During waking hours, the flow of CSF is generally restricted. And this restriction prevents the removal of toxins throughout the day, the byproducts of whatever it is that our brains are thinking about.

When we sleep, however, the brain gratuitously flushes the ventricles with CSF and removes the toxins, supplying the brain with new resources and preparing it for another wave of sensorium upon awakening— reinforcements, if you will.

And this is why it’s good to get a good night’s sleep. On a long enough time scale, staying awake is literally poisonous.