Cruise through life...are you a tenured full professor with a funded chair? ;-)
Programmed cell death is part of life and it is not surprising that
neurons and synaptic connections change throughout a life span. Lets
play a numbers game.
If at age 15 one typically uses a fixed percentage of neurones
(organized in circuits), it stands to reason that as cells die, some
of the redundant circuits are lost. If there is a finite number of
circuits needed for a function, the percentage of neurones would
conceivably increase (15 of 92 versus 15 of 100.) Hence, I use a
greater percentage of my ebbing brain capacity today than yesterday.
Coincidently, I have fewer nephrons, islet cells, patent capillary
beds, and muscle fibers. When I am in my dottering 90's I will
likely be using everything and anything I can to waddle to the head,
to the table, and to my computer screen where I will suck lemon drops
to provoke my three remaining salivary glands to moisten my dried old
mouth. 100% efficiency may not be all it is cracked up to be, but
I'm not giving up until I get it perfect, even if it takes me another
100 years.
We use all of our brain cells in a somewhat orderly fashion, from time to time.
A PET scan can be used to monitor metabolic activity of neurones in
the brain. Cells in use expend more energy than cells at rest. The
distinctive patterns of activity associated with specific tasks
demonstrate the involvement of untold neurons, many of which are not
active most of the time. An area that is consistently inactive
typically reflects a pathology. But virtually every neuron in the
brain remains metabolically active and functional, unless it becomes
isolated, impoverished of nutrients and synaptic inputs.
Our conscious levels and intellectual capacities vary from time to time.
Clearly our brain has a range of calculating "gears". Most of us
experience heightened awareness and intellectual prowess following
modest stimulation by caffeine. Abuse of amphetamines is associated
with accelerated powers of calculation that eventually overload and
precipitate a deep and profound depression. The immense emotional
"kick" that results from the ability to think underpressure reflects
the adaptive capacity of our brains from moment to moment.
In calculating basal metabolic rates, it is generally assumed that
ion pumps consume about 600 Kcal per day. Every neuron in the body
needs pumps to maintain ionic asymmetries. It would be a waste to
spend all that energy on cells that are not needed. We use every
cell in our body, we use every neuron, but not all at the same time...
Men vs Women ;-)
From a developmental perspective, female is the default course of
human development (turtles too.) Males lack the genetic information
needed to be female. It astounds me that women keep harping about
our loutish ways...we are the victims of evolution. Males are the
victim of thousands of generations of mate selection- women do choose
their mates- that we have arrived at this sorry state. We have 0.5%
less genetic information at our disposal (Y versus X chromosomes.)
Now 0.5% does not seem like much, but it happens to be a very
important 0.5%. The gene for dropping the toilet seat is X linked.
We need to be bigger because we need the additional mass because
redundancy does not win arguments. We are so inefficient, we need
larger salaries to get by. Have you priced 15 inch high profile
radials lately? Whew! Men buy pickups because the smaller passenger
area means fewer folks to entertain or keep track of. Women are
smarter and have raised male anxieties to the uptight point where we
whistle when we pass air.
enjoy your weekend.
rlh
>Richard Hall (rhall at uvi.edu) wrote:
>: This is getting nowhere, slowly and painfully.
>: If one assumes that natural selection acts on phenotypes resulting in
>: improved fitness, it seems reasonable to assume that anything not
>: contributing to fitness would be eliminated.
>>I think that part of the idea that we need only 10 % blahblahblah, is that
>at some point you might need 100%, while you are developing and making
>connections, but once all the circuitry is established and you just cruise
>through life, you only need 10% of what is there. Consider the
>scientifically established fact that the majority of your connections and
>even neurons disappear between fetal stage and teenage years.
>> Didier
>>--
>Didier A Depireux didier at isr.umd.edu>Neural Systems Lab http://www.isr.umd.edu/~didier>Institute for Systems Research Phone: 301-405-6557 (off)
>University of Maryland -6596 (lab)
>College Park MD 20742 USA Fax: 1-301-314-9920
