Increased blood flow detected by fMRI scans?
zhil at online.no
Thu Oct 25 15:46:21 EST 2001
"John H." <John at faraway.com.au> skrev i melding
news:_KVB7.1322$Fi4.73149 at ozemail.com.au...
> > Yes, it would be nice if I could answer these questions, but I'd say
> > they were measuring in monkeys that were unconscious, they would not
> > measure the real energy usage.
> > Protein production for growth of the synapses are probably the greatest
> > of oxygenated blood.
> No, my bet is is ion channel function(for cellular ion homeostasis and
> transmission) is the greatest user of resources in neurons. Eg. various
> calcium pumps are continually pumping against a substantial gradient. They
> don't just switch on for a while, more probably are maintaining a basal
> level of function. I don't like the term 'electrical signals' because in
> neurons transmission is a very demanding process, not just some flow of
> electrons but the continuous synchronous activities of a plethora of ion
> channel types. The energy to create new synapses in no way compares to the
> amount of energy required to maintain normal ion homeostasis because new
> synapses are relatively rare. Synapses come and go, degraded and
> probably even in long term memory, but even a resting brain is
> expensive. 2% bodyweight, 20% of all resources.
Ok, thanks for the input.
And I didn't add the extra usage by the new synaptic connections.
More synapses, more energy-usage.
It probably follows an exponatial rate, as there's an upper limit of how
many synapses a neuron can handle.........
> If fMRI was measuring synaptic formation activity, then in the cases of
> term memory at least there should remain activity in the region after the
> individual has stopped observing the stimulus. The area should remain
> activated as indicative of ongoing synaptic formation. That does not
> or at least I don't know of it, my understanding that fMRI relates to
> immediate cognitive activities.
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