[Neuroscience] Re: Neuronal activity in the brain

[Matthew Kirkcaldie]

In article <ehdkh3$are$1 from mailhub227.itcs.purdue.edu>,
 "Fijoy George" <tofijoy from yahoo.co.in> wrote:

> Hi all,
> 
> Would someone be able to help me with the following question?
> 
> When we look at the neuronal activation areas in Functional Magnetic 
> Resonance Images obtained from various experiments, we see that in each 
> area, the activity is most intense at the center and slowly declines towards 
> the boundary. Now, suppose we were to actually measure the neuronal currents 
> in the activation areas. Will the current amplitudes follow the same 
> pattern? That is, will the current amplitudes be highest near the center of 
> the area, and smoothly decline toward the boundary?
> 
> Thank you very much
> Fijoy

Fairly unlikely, in my estimate.  The nearest correlate to fMRI signal I 
know of is firing rate in neurons, but the decrease at the edges of the 
fMRI signal is likely to be a combination of measurement artifact 
(limited resolution of the technique) and the anatomy of the blood 
vessels - in particular, anastomoses between vessels, spreading 
increased blood flow around the activated area.  I'm not exactly sure 
what you mean by "neuronal currents" -  firing rates?  Evoked 
potentials?  More info would allow a better answer.

      Cheers,

         Matthew.