October 28, 2016

Impermanence Often Wrongly Described as Plasticity

Impermanence Often Wrongly Described as Plasticity

Everything changes. The largest chunk of uncertainly is impermanence. There are constant paradoxes and contradictions built into our brain function. We must be alert to notice and respond to changes but, at the same time, attempt to be stable and consistent. Our visual system is designed to notice minute changes but ignores most of the movement around us to create the illusion of a stable world in consciousness. Growth, development, and aging are the main expressions of predetermined impermanence that combines DNA programming with environmental opportunities and hazards. You could argue that brain growth and development changes are most vigorous in the first 20 years of life; later, after a brief period of relative stability, degenerative changes take over, accelerating with advancing age.

Too often, I am an unwilling victim of television news nonsense and plasticity is a current favorite topic. Brain damaged survivors are shown with plausible mental abilities, as if their example refuted neuroscience beliefs. The term plasticity has crept into neuroscience jargon and should be erased from the vocabulary. I am not aware of the source of plastic metaphor and can only assume that it refers to a material that can be coaxed into different shapes by heat and pressure using a variety of machines. I cannot see any connection between the malleability of plastic and the constant flux that characterize brain function.

Even smart, educated humans participate in these media delusions. For example, I was surprised to read a report by Allison Gandey from a meeting of the American Academy of Pain Medicine that revealed basic ignorance among a group of smart professionals. She stated: " Some suggest the discovery of neuroplasticity is the most important breakthrough in neuroscience since the revelation of the brain's basic anatomy. Proponents say the brain is pliable and can alter its structure and function. " One MD even admitted:" We used to think the brain was wired after about the first 3 years and what you had was what you got and you work within that because there was no chance of changing it. If on top of that the brain was damaged, you had to live with that damage. Neuroplasticity says that's not so — the brain is changing all the time."

It is true that the brain is changing all the time, but it is not true that this is a discovery or a breakthrough. It is also not true that lost function is easy to recover. While it might be true that limited recovery of function is possible after brain injury, it is more true that loss of function tends to be permanent after the initial recovery in the first few months. You might consider that some physicians are lost souls with erroneous assumptions and unrealistic fantasies, but then, I also read rather naïve comments about plasticity in the neuroscience literature.

A big problem we have is that while the world around us changes, we also change and the biggest changes occur in our brain. The idea of one personality remaining stable over many years is actually absurd, but we are tempted to believe in an enduring self. An astute observer will notice that each day brings forward a series of different personalities within one body. I call these personalities eigenstates. The self is not one entity but rather consists of a collection eigenstates that serve different needs, roles and capabilities. Some eigenstates are built it others are learned and remain open-ended, evolving with changing circumstances. '

Neurons and glial cells are the brain cells that a manifest all the properties of mind. The study of neurons could be considered ne plus ultra, the quantum mechanics of biology. Neurons come in different shapes and sizes but have the common property of constant changes receiving and sending information. Neurons conduct discrete signals as electro-chemical pulses, known as action potentials or “spikes.” The signal passes from one neuron to another by the secretion of chemical neurotransmitters in synapses. There are trillions of synaptic junctions in the human brain. Learning occurs at least in part by changes in the number, strength and kind of synaptic connections.

Learning, in the best case, is adaptive impermanence that requires changes to brain structure and function. We will consider, for example, that learned movements are generated from dynamic cortical maps based on fields of activity that converge and diverge in complex patterns. Over time, the pieces of the map change with learning and practice, so that the construction of cortical connections is always in flux. This impermanence allows us to learn at all stages of life, to adjust to changing environments and, to some extent, to work around disabilities that arise from brain injury and disease.

Sleep is a transformative time of day. Cortical neurons are active, reviewing events of the day. During slow-wave sleep, the cortex disconnects from other parts of the brain and concentrates on memory consolidation. The emergent properties of the sleeping brain are unpredictable. You could argue that the events of each day will alter the brain during sleep and a new person wakes in the morning.

From Neuroscience Notes by Stephen Gislason MD