Steve, The image posted at http://neuroelectrodynamics.blogspot.com/p/spike-directivity.html shows continuous extracelular recordings, in vivo -MTL region, human brain, not intracellular data. One can isolate and analyze spikes generated by a single neuron using the recorded signal (see the spike sorting procedures) . The attenuation is strong enough, if two neurons simultaneously generate APs and are close to the electrodes then the shape of recorded signal visibly changes and one can easily exclude those APs. The image of AP propagation can be constructed for every spike. You can read the "literature", little information that can be related to this discussion, the issue can be further explained but I feel is beyond the excellent topic posted here
Dorian On Sat, Jun 30, 2012 at 12:12 PM, Steve Richfield <[email protected] > wrote: > Dorian, > > I'm not sure we are on the same page here. Most of the neuronal activity > you see in the literature is intracellular, where the electrode is put into > the cell to observe what is happening. This has the advantage of providing > an absolute depolarization voltage scale. Most of these recordings show a > millivolt (mv) scale on the left. This has the major disadvantage of often > killing the cells involved, often so fast that nothing useful can be > recorded. > > However, there are also extracellular recordings, where electrodes are > placed near cells to observe things. These have the major disadvantage > that, with cells being all packed in together with NO space between them, > you can't avoid recording several other cells in addition to the one you > want. Hence, there can be no absolute depolarization voltage scale. > Depending on the setup, you may be recording millions of other cells in > addition to the one you want. This may be great for measuring overall > activity in an area as EEGs do, but is pretty useless for watching the > activity of any single cell. > > On Sat, Jun 30, 2012 at 11:18 AM, Dorian Aur <[email protected]> wrote: > >> I'm not sure that you recorded action potentials (APs) . > > > Again, MOST of the recordings of neuron spiking in the literature are > intracellular. Just look for the "mv" scale on the left to show that they > have paid attention to seeing exactly what is happening inside the cell. > > >> Do you have a clear image of recorded spikes. >> > > I haven't done this stuff in a LONG time. > > Steve > ================== > >> On Fri, Jun 29, 2012 at 4:34 PM, Steve Richfield < >> [email protected]> wrote: >> >>> Dorian, >>> >>> Look again at those graphs. Action potentials come and go in >>> sub-millisecond times, yet those "spikes" are tens of milliseconds long. >>> Either there is something wrong with the apparatus (I always used coaxial >>> "driven shields" to eliminate the effects of capacitance, etc), or there >>> are LOTS of neurons involved in making those slow "spikes". >>> >>> On Fri, Jun 29, 2012 at 3:53 PM, Dorian Aur <[email protected]> wrote: >>> >>>> The signal from every "antenna" can be used to see what happens >>>> inside the cell during action potential generation (1ms) in vivo, see the >>>> papers, >>>> http://neuroelectrodynamics.blogspot.com/p/spike-directivity.html >>> >>> >>> Note that most people expect 1/r^2 dropoff with distance, but with long >>> neurons, the dropoff is only 1/r. Worse yet, if you haven't well grounded >>> things so that dropoff can happen (and the "floating" nature of the curve >>> literally screams of bad grounding), there is NO dropoff at all with >>> distance - you see everything there is to see, all superimposed, like in an >>> EEG. Indeed, note the similarity in appearance with an EEG. >>> >>> >>>> With single electrodes in vitro,the phenomenon cannot be observed >>>> >>> >>> Thereby proving that it doesn't exist. >>> >>> Anyway, our discussion here illustrates the sorts of disagreements that >>> so often exist when neuroscience meets computer science. It takes >>> scrupulous attention to details to be able to capture things you can really >>> believe, and there are SO many subtle indications of things that aren't >>> really happening. >>> >>> Speculation on inadequate evidence is GOOD, because without it the field >>> could not advance. However, be careful not to become too invested in your >>> speculations. To illustrate, I first "proved" that at least some neurons >>> communicate the logarithms of probabilities of assertions being true, only >>> to decades later show that more likely those same neurons are communicating >>> the derivatives of the logarithms of probabilities being true. >>> >>> In this business there is very little that can be proved, only >>> disproved, and then only under certain particular circumstances. >>> >>> Steve >>> ================ >>> >>>> On Fri, Jun 29, 2012 at 2:39 PM, Steve Richfield < >>>> [email protected]> wrote: >>>> >>>>> Dorian, >>>>> >>>>> On Fri, Jun 29, 2012 at 2:05 PM, Dorian Aur <[email protected]>wrote: >>>>> >>>>>> Excellent topic. During every action potential every neuron *solves* >>>>>> an n-body problem analog ‘doing’/ execution and the information is >>>>>> electrically carried and integrated in the brain >>>>>> http://neuroelectrodynamics.blogspot.com/p/spike-directivity.html *The >>>>>> fundamental process of computation by physical interaction in the brain >>>>>> has >>>>>> been widely misunderstood*. >>>>>> >>>>> >>>>> I think the thesis of this site is misdirected. extracellular >>>>> recording involves using a sort of "antenna" that collects not only the >>>>> cell you are near, but also other nearby cells all added together. Hence, >>>>> OF COURSE you will see apparent modulation, even when it isn't actually >>>>> there. >>>>> >>>>> There has been most of a century of intracellular recording, where >>>>> they impale a neuron with an electrode and look at what is happening >>>>> inside >>>>> the cell. Those experiments have observed NO such modulation. >>>>> >>>>> It appears that the value being transmitted is a function of the >>>>> separation between spikes. This is NOT linear, and closely placed spikes >>>>> count as MUCH more than isolated spikes. >>>>> >>>>> However, information travels BOTH ways on axons, and there may even be >>>>> more than one "forward channel" as ions travel both ways along axons. >>>>> >>>>> However, only a tiny percentage of neurons, mostly ones with really >>>>> long axons (often long enough to see even without a microscope) to >>>>> transmit >>>>> their information to a distant place, even produce spikes. The vast >>>>> majority of neurons simply vary their potential as they "compute", all >>>>> without producing any spikes. >>>>> >>>>> Steve >>>>> >>>>> *AGI* | Archives <https://www.listbox.com/member/archive/303/=now> >>>>> <https://www.listbox.com/member/archive/rss/303/17795807-366cfa2a> | >>>>> Modify <https://www.listbox.com/member/?&;> Your Subscription >>>>> <http://www.listbox.com> >>>>> >>>> >>>> *AGI* | Archives <https://www.listbox.com/member/archive/303/=now> >>>> <https://www.listbox.com/member/archive/rss/303/10443978-6f4c28ac> | >>>> Modify <https://www.listbox.com/member/?&;> Your Subscription >>>> <http://www.listbox.com> >>>> >>> >>> >>> >>> -- >>> Full employment can be had with the stoke of a pen. Simply institute a >>> six hour workday. That will easily create enough new jobs to bring back >>> full employment. >>> >>> >>> *AGI* | Archives <https://www.listbox.com/member/archive/303/=now> >>> <https://www.listbox.com/member/archive/rss/303/17795807-366cfa2a> | >>> Modify <https://www.listbox.com/member/?&;> Your Subscription >>> <http://www.listbox.com> >>> >> >> *AGI* | Archives <https://www.listbox.com/member/archive/303/=now> >> <https://www.listbox.com/member/archive/rss/303/10443978-6f4c28ac> | >> Modify <https://www.listbox.com/member/?&;> Your Subscription >> <http://www.listbox.com> >> > > > > -- > Full employment can be had with the stoke of a pen. Simply institute a six > hour workday. That will easily create enough new jobs to bring back full > employment. > > > *AGI* | Archives <https://www.listbox.com/member/archive/303/=now> > <https://www.listbox.com/member/archive/rss/303/17795807-366cfa2a> | > Modify<https://www.listbox.com/member/?&;>Your Subscription > <http://www.listbox.com> > ------------------------------------------- AGI Archives: https://www.listbox.com/member/archive/303/=now RSS Feed: https://www.listbox.com/member/archive/rss/303/21088071-c97d2393 Modify Your Subscription: https://www.listbox.com/member/?member_id=21088071&id_secret=21088071-2484a968 Powered by Listbox: http://www.listbox.com
