[Neuroscience] Re: Neuronal activity in the brain

Fijoy George via neur-sci%40net.bio.net (by tofijoy from yahoo.co.in)
Sun Oct 22 14:20:28 EST 2006

Thank you for your reply, and sorry about using loose terminology in my 
question.  I hope I am making myself clear in the following.

We know that the primary sources of electrical currents in the brain are the 
pyramidal cells in the cortex. We also see that the pyramidal cells are 
normally oriented to the cortical surface. Suppose that a particular portion 
of the cortex (a cortical patch) is activated during a task. Suppose we 
measure the *current density* normally oriented to the cortical surface at 
various locations in the patch. Now, will the amplitudes of the current 
density be maximum at the center of the patch and slowly decline as we move 
along the cortical surface away from the center?

Thank you very much

"Matthew Kirkcaldie" <m.kirkcaldie from removethis.unsw.edu.au> wrote in message 
news:m.kirkcaldie-B07890.10410122102006 from news.sydney.pipenetworks.com...
> 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. 

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