Information on BiPolar Disorder

Alex:
> >>>Yep, I know the work well … it’s a really cool idea with a couple
> >>>limitations at present … primarily, the heterogeneous distribution of
> >>>ion channels present across a neuron makes it hard to interpert signals
> >>>(e.g., you might have capacitive coupling or a leak current or anything).
> >>>The videos are cool as well – anyway, it would be better if they could
> >>>make an array of eos-fets rather then via-ed mosfets but they’re harder to
> >>>scale … enjoy your retreat and let me know about the cells … I
> >>>appreciate everything,

Me:
> >>Alex,
> >>
> >>Thanks for the interesting stuff to think about. Is the heterogeneity
> >>really an
> >>issue? Are the MOSFETs really limited to sensing such a small area that they
> >>would be susceptible to ion channel inhomogeneities? (I’m thinking of the FETs
> >>as really tiny bipolar electrodes here, which I think it correct…) Are the
> >>source and base terminals for each FET very close together in a chip
> >>like this?

Alex:
> > Hey Neville,
> >
> > So, in short, the answer is yes – some of their older papers document this
> > well … If you compare a patch recording (x) with what the FET sees (y),
> > sometimes x=y, sometimes dx/dt = y, sometimes -dx/dt = y, and everything
> > in between. The real issue arises from the manner in which the FETs are
> > gated – basically, you’re using gradients in the ion concentration as the
> > gating mechanism … if you have a distribution, and those channels have
> > different polarities and opening times, it becomes very hard to figure
> > out what’s going on … and even without ion channels, you can get a
> > capacitive signal from the membrane. In CMOS, there’s only one carrier
> > (the electron), here everything is much more complicated … finally, to
> > help you think about size, remember that the FETs are at 7 um pitch -
> > that means that within 7 um, you have a source, a gate, and a drain for
> > the FET and a spacer area (between it and the adjacent FET) … this
> > means that the gate is relatively small … I hope this helps,

Me:
>> I see what you mean… I can imagine that the terminals
>> could be small enough that you would have issues with
>> spatial inhomogeneity. I guess the best solution would be to
>> pack the chip at an even higher density. Then, you’d hope
>> that certain spatially continguous sets of FETs covary
>> together enough that you’d believe that they were controlled
>> by a single cell…

Alex:
> Neville,
>
> I should point out that it’s a brilliant idea – it just hasn’t proven
> itself yet … you’re right about generating algorithms to interpret the
> data – the big problem then is the size of the data stream – 2khz*10^4
> transitors*experiment time = a lot of data to store and then correlate
> and then analyze … it’s daunting to say the least … we thought about
> modifying Fromherz’s FET design originally (and probably will do something
> like it in the not so distant future), but opted not to based on the fact
> that, for large data sets, you want to be positive from which neuron
> you’re recording … also, we wanted to study intrinsic changes (e.g.,
> resting membrane potential) …