Brain networks

also see: Anatomy, physiology & brain networks, in this section

Aim of this article: answering some questions raised in forums and clarifying what networks do and how they develop.

Readers: Tell us if it works! Also, please tell us anything that you feel would explain stuff better, bearing in mind that we’d like it to be less wordy but clearer. After reading it, consider whether you now have a clear idea of what networks do what? If not, what’s missing? What doesn’t need to be in here? Feedback in the forums please!

Networks –clarifying what they do and how they develop

Who are you?

‘Game Space’ of network connections or ‘wiring’ across one half of the brain. What we are seeing here is a map of axons; connections between networks; not the neuron cell bodies themselves. The clear line of blue from front to back about two thirds up is the thin part of N6, just above the Corpus Callosum marked in red (we can’t see most of it because it runs laterally from left to right). We can’t see much of each lateral hemisphere either, but we can at least appreciate how ‘networks’ are not tidy little modules geographically separated and neatly wired together; in fact they more closely resemble a dangerous server room.

The example above may not be a fully developed brain, despite the fact it is an adult one. The concept of ‘development’ as linear does not accord well with any species having a life cycle –a fully developed body, for example, is not at all the same as one that has completed its cycle! By developed we mean ‘reached the peak potential of its maturity’ and for the brain and body this means it needs to have done things and learned things as well as grown things. Brain development with optimal input still takes about 25 years. If things are not optimal, development at any stage may slow or stop.

The speediest part of growth should occur in the womb, at about the following pace:

During the 40 weeks of pregnancy, neurogenesis causes the fetal brain to increase rapidly in size and complexity. In humans, there is still a lot more development to go after birth, most of it involving dendritization and synaptogenesis. At every stage from conception, development can be slowed or stopped.

A healthy baby's brain has many more neuronal connections at age two than it does at birth. An unhealthy brain may not. This is the basis for educating parents on diet, anxiety control and drug use in pregnancy, and urging parents and caregivers to support childrens’ development by providing a stimulating enriched (natural) environment that includes appropriate input for all 5 senses.

There are a number of conditions that can result in retardation (retardation literally means ‘holding back’) of the normal development of the brain before birth, during birth, or during childhood. For example, genetic abnormalities can cause disorders that affect a child's development or metabolism, which in turn can cause problems in the brain. Sometimes the brain is damaged or just does not develop normally before birth, as occurs in the condition called cerebral palsy. If the mother drinks alcohol or does not take in sufficient vitamins or other nutrients in her diet during the pregnancy, brain and spinal cord development can also be affected. Ongoing development is hindered or enhanced by available input and by distraction.

What do you like?

Activity in the Medial OrbitoFrontal Cortex (N6) and in N3 correlated with the reported pleasantness of drinks.

In this study all extraneous data has been ignored, only the areas firing in multiple subjects or scans in response to the same input has been highlighted. This is the case with most scans of this kind. They don’t reflect what’s going on in the brain; just highlight a small part of it that the researchers want to study.

Whom do you trust?

Friend (L amy) or foe (Rt amy), -benefit or danger?

And if you just can’t decide……….

Both amygdalae –keeping your options open.

When a situation holds both benefits and dangers, we stay alert but open minded.

We may from there move into conditional or unconditional trust:

Conditional trust selectively activates the ventral tegmental area in the paracingulate cortex, a region linked to the strategic evaluation of expected and realized reward [N6], whereas unconditional trust selectively activates the septal area, a region linked to social bonding behavior [N3].

The interplay of these neural systems supports reciprocal exchange that operates beyond the immediate spheres of kinship, one of the distinguishing features of the human species. In situations where N6 is lacking, unconditional trust is given without consideration, which is another way of saying people in whom N6 is not developed are easier to deceive. Young children are ‘gullible’ because this area hasn’t fully developed yet, and the same excuse is unfortunately applicable to many adults.

What are you paying attention to?

Even a fairly simple task like recognizing something by shape and motion will engage several networks:

P = Posterior (rear); A = Anterior (front)

You can see activity in N1 & 2 marked in gray here. The area in black above them in the top left picture is part of the major association area in N3, which will be comparing the input to examples from eidetic memory. Further forward and to the left N5 joins in, probably calculating or deducing the finer details of motion (N2 having recognized the basics). It’s not necessary in this task to recruit neurons from N4 or N6.

Some tasks use multiple networks:

This person is watching a video and answering simple questions about it such as ‘is the guy holding the object with all five fingers?’ The pic on the left is the right hemisphere and vice versa. You’ll notice the motor cortex is joining in even though the guy’s not moving, just because of paying attention to the movements. All networks except N5 seem to be involved in some way, with a lot of activity over N3’s association area.

We know what some of the networks’ tasks will be because we know what sort of processing goes on in each network. Here’s a reminder below:

Here is a table showing what each network processes and pays attention to, together with some of their associations.

Many tasks use multiple networks, and the same network can perform many tasks as you can see in the activities above in which people are listening to spoken language or music; but sometimes they are quite specific. Below is a scan of N5 doing arithmetic:

The little panels on the right show groups of neurons in the same area and their strength of firing for different tasks. Darker squares indicate more intense firing.

What happens when you meditate?

Lots, but this is some of it. The area in the bottom two pics is part of a main association area between networks, normally considered a part of N3. The section firing in the two top pics is part of the ‘bridge’ area between N3 & N6. Meditation seems to increase synchrony between networks.

With continued meditation, this happens:

As seen from above through a slice from the middle of the brain. From the side it looks like this:

We can see N3 and N6 blazing away. But when you view this from the front, you can see where some spiritual imagery gets its intuitive ideas from:

(medial Pre Frontal Cortex & Anterior Cingulate Cortex; N6, plus bits of the cingulate ‘bridge’).

This pic has been put around the net as an ‘MRI of the third eye’ or ‘the house of god’ by some hopefuls who believe that god’s house is there. If this were so, god would have to be really small, like, microscopic; and no proof is as yet forthcoming. But I love the uncanny reflection of the back of the brain through the eye sockets in this one.

Interestingly, we also use these parts when making decisions:

And sometimes the whole of the N3 /N6 connection gets involved:

If there is emotional instability, though, this doesn’t happen. Only the areas in N3 –associated with emotional processing- light up when making decisions. Notably absent is activation of the dorsolateral prefrontal cortex, the part of N6 most associated with reasoning. The researchers who discovered this hypothesized that the sentiment-driven processes that lead to biased judgments likely occur outside of awareness, and are distinct from healthy reasoning processes when sentiment is not engaged. This seems to demonstrate the extent to which sentiment can truly distort our thought processes — to the extent of shutting down normal reasoning altogether — without our awareness even that this is happening. But we cannot read cause and effect into a correlation. What we know is that when there is emotional instability and anxiety, N6 is often unresponsive in decision making. What we can’t assume is that the former causes the latter. It could be the other way round, or a third factor could be affecting both. That’s why it’s a hypothesis and not a theory.

Order in development

Networks develop in the order they are numbered. The continuing development of all networks requires gene transcription triggered by specific events. Initially networks 1,2 and 3 need specific input cues from the outside environment on order to fully wire up. Once this is achieved, each network awaits the trigger of a critical mass of input from those before it in order to fully wire up. Development from there depends on regularity and intensity of integrated use with healthy input.

Why N3 is special

N3 contains the amygdalae, and the structures below:

Hippocampus (colored). The brain is sliced in half horizontally; the front of the head is to the left. The brain is in the same position in the next two pics.

Putamen –part of the striatum, and together with the caudate nucleus (they contain the same type of neurons and circuits) the border between N3 & frontal networks.

The way your networks themselves are wired up is unique to you and your stage of development. It is invariably complex and can’t be covered in something this small. But there is a circle of circuits in N3 that connect it with all surrounding networks, and the putamen is a part of that (so are the globus pallidus, substantia nigra, and caudate nucleus).

Thalamus. The thalamus is a major relay station for both input and output. It is the thalamus that runs the ‘defragging’ program when we sleep, and regulates arousal, level of awareness and activity. Most importantly, this is where translation from one kind of input to another takes place (where input is coded or decoded and forwarded to the relevant nets).