Default Mode Network # 4 Final
Happy New Year 2018

Default Mode Network Posting # 4

Posting # 1: Default Mode Network (DMN) is aerobic glycolysis (AG), AG is defined as glucose utilization more than that used for oxidative phosphorylation despite sufficient oxygen to completely metabolize glucose to carbon dioxide and water. AG is present in the normal human brain at rest, it is highest in the regions that relate to memory and emotion. During neuronal activity, i.e., when we see or hear or touch or smell or do a job, the AG decreases in these regions and metabolism increases in those regions that are activated locally by neuronal activity.

Posting # 2: In terms of biochemistry, glucose is the principal energy source of energy for our brain; there are transporters that carry glucose to the brain; to generate energy, 90% of glucose is used by oxidative pathway and 10% of glucose is used by “aerobic glycolysis” since it occurs in presence of oxygen. I said that the brain uses this combination pathway is to preserve some carbon for remodeling and repair of synapses and to protect against oxidative stress. I said also that there are 3 types of brain cells which use these glucose pathways differently and coordinate with each other to achieve the goal of smooth organized brain function.

Here is the metabolic energy organization of the 3 cells that coordinate with each other, they are astrocytes, neurons and oligodendrocytes. Blood flows through the capillary, glucose is taken up by astrocytes; metabolize it by aerobic glycolysis up to pyruvate/lactate and then gives lactate to neurons to oxidize it to CO₂ and H2O. Neurons are rich in mitochondria and astrocytes lack mitochondria to match their role.

Rationale for this organization in the brain, synapse is the site of action, it is the connecting part of one neuron to another, the neuron sends the signal to the receiving neurons by firing a chemical (neurotransmitter). The neuron(s) that receives the signal becomes electrically active and passes the signal to the next neuron. Now the neuron that sent signal must remain in reduced redox state to send the next firing signal, the neuron that received the signal must come back to its original state to receive the next firing signal. Importantly, all these actions occur within milliseconds. It is an energy consuming process. Two points: One, this can’t be done by neuron alone, it requires a second player, to provide instant energy, that is where astrocytes come to play. They convert glucose to lactate and provide instant energy. Neurons take up the lactate and burn it to CO2 and H2O, to provide maximal energy for transmission. Neurons have a sheath of myelin to reduce energy loss, but they can’t do for long distances, so we have node of Ranvier, a way station that provide us an opportunity to generate additional energy, this is where oligodendrocytes come to play, they do similar function to that of astrocytes, provide instant energy and energy bars for neurons to push the transmission further. That is the sum of the game on neurotransmission. The second point is, when you are not attending to physical activity, engaging with the external environment, or carrying on a conversation. Inattention DMN, also consumes energy, that is why you don’t see any difference in blood flow, glucose and oxygen consumption as we age. Take home lesson: quality of glucose consumption rather than the quantity makes all the difference.

Posting # 3: There is a change in the way how the brain metabolizes glucose (AG) as we age. We are using glucose less toward formation of new memory and emotion at older age than when we were younger. If we don’t, what was an asset when we were younger, all the energy spent towards emotion and memory, now is a liability at older age, you don’t want to live in the past, it is good to remember but not live in the past. If our mind starts to live in past and we lose all the contacts, we have developed that defines you as who am I?

Solution: Mindful Meditation, as we age, what can we do to decrease the blood flow to the regions of memory and emotion and increase to the blood flow to the regions that relates to what we are doing. Here are four conscious exercises that are proposed to help us as we age

Meditation

I wish that I had done this as a daily routine, spend half-an-hour each day just close the eyes and focus on the breathing. It is easier said than done but setting aside 30 min each day will change AG over a longer period. Here is the published result: “We found that the main nodes of the default-mode network (medial prefrontal and posterior cingulate cortices) were relatively deactivated in experienced meditators across all meditation types. Furthermore, functional connectivity analysis revealed stronger coupling in experienced meditators between the posterior cingulate, dorsal anterior cingulate, and dorsolateral prefrontal cortices (regions previously implicated in self-monitoring and cognitive control), both at baseline and during meditation. Our findings demonstrate differences in the default-mode network that are consistent with decreased

mind-wandering. As such, these provide a unique understanding of possible neural mechanisms of meditation”.

Exercise. Making physical exercise a part of your daily routine is the next best thing that you can do to maintain the difference in aerobic glycolysis at rest and during activation. It refreshes the brain. When you exercise, I mean simple, turn of TV, focus on your breathing and where your feet are in space as you move. 

During brushing your teeth and taking bath. You can't go a day without brushing your teeth, taking a bath, making this daily task the perfect opportunity to practice mindfulness. Feel your feet on the floor, the brush in your hand, your arm moving up and down. Einstein said he did his best thinking while he was shaving--what he was really doing in those moments was practicing mindfulness! The same is true when you take bath. Focus on what you need to do the whole day, plan your day, what is the app message you want to send to your family? What is the dinner plan? What do I need each member of the family to do for that day, set reminders?   

Evening, men cook and do the dishes. "washing the dishes to wash the dishes". When you give yourself over to the experience, you get the mental refreshment of a mind-body practice and a clean kitchen. For men, if you can cook, that is the best mental relaxation that you can come up with, but what is important is you must love it to do it and not feel it as burden. It's multi-tasking at its best! I have been doing this for the past 30 years.