Well Rydi, I finally found the anatomical basis for why you hate 18 year olds. I recall we had a conversation about people younger than about 23, I still agree and now here comes the science!
Two essential components of neuroscience are needed to explain the observed phenomena.
Firstly, Myelin. A neuron has exactly one axon, which is a long process that extends and synapses upon another neuron, and it is down this axon that action potentials are conducted and forms the anatomical basis for the 'circuitry' that neuron complexes demonstrate. Each axon is surrounded by a sheath called myelin, which accelerates the action potential transmission. "slow" axons, that are un-myelinated, have been clocked no faster than 30 meters/second, and as slow as less than 1 meter per second. This seems fast, but 'fast' axons, with a myelin sheath, conduct as fast as 120 meters/second, and usually no slower than 100 meters/second. Now, this affects a great many things, action potentials must accumulate on a target neuron in order for the target neuron to fire its action potential, and you can see how a great many excitatory and inhibitory neurons all interconnected could propagate action potentials and, in a complex enough system, form the basis for storage, retrieval, and processing of information. Recall that in multiple sclerosis the pathophysiology is 'demyelination'.
Second, association cortex. For every sense the body has, as well as emotion, there is an association cortex. We have seen demonstrated through studies of lesions in living people that these areas are where 'higher order' though takes place, and stimuli are correlated here with emotion. Humans have vastly more association cortex in their brains than any other living creature, even dolphins, and we think this is why we have rocketships and they don't. Memory seems to be stored in the association cortex, as well as the emotional connotations of those memories.
Now that that's out of the way, I can reveal that until the third decade of life, the association cortex does not finish myelination. That's right. 30. So, the anatomical basis for processing of information balanced with emotion and memory does not reach it's most ideal configuration until somewhere in the mid to late 20s.
In the absence of myelin, these neurons would still transmit their pulses, but the pulses would fade out before enough pulses accumulated to cause the desired response. So, it takes more to do the same, which generally means you get less.
/end science.
Moderator: Mods
makes sense.
oddly, the brain shrinks as we age as well, but seems to become more efficient at doing what it is used to doing, and increasing crystalized memory, which makes up for the cell loss that occurs, though reaction times and adaptation/fluid memory do suffer somewhat. if i remember right. it's been a while since i dealt with that. should be dealing with it now, since i'm in biopsych, but my class sucks.
i do seem to remember that the point at wich a significant shrinkage occurs coincides with the completion of growth at around 30 though...
oddly, the brain shrinks as we age as well, but seems to become more efficient at doing what it is used to doing, and increasing crystalized memory, which makes up for the cell loss that occurs, though reaction times and adaptation/fluid memory do suffer somewhat. if i remember right. it's been a while since i dealt with that. should be dealing with it now, since i'm in biopsych, but my class sucks.
i do seem to remember that the point at wich a significant shrinkage occurs coincides with the completion of growth at around 30 though...
Threading the Gerbil since 1982
a lot of memory is actually created by the breaking down of neuronal connections, as well as the establishment of new ones. Also, it's been recently shown that even the adult brain can repair some types of damage, and that the common and widely accepted axiom that brain tissue can't heal is false.
Yeah, it shrinks. It seems to me that this is probably expansion of the sulci which increase the surface area of the brain. In the newborn, the brains surface is smooth. It develops it's typical and classic 'gyri-sulci' appearance over time. It goes from 300g to 1400g by the time you reach 30, so it would make sense that it's 'shrinkage' is an increase in surface area and a decrease in weight. Like a finely tuned machine.
But not in 18 year olds.
Yeah, it shrinks. It seems to me that this is probably expansion of the sulci which increase the surface area of the brain. In the newborn, the brains surface is smooth. It develops it's typical and classic 'gyri-sulci' appearance over time. It goes from 300g to 1400g by the time you reach 30, so it would make sense that it's 'shrinkage' is an increase in surface area and a decrease in weight. Like a finely tuned machine.
But not in 18 year olds.