X-Message-Number: 7901 Date: Thu, 20 Mar 1997 08:38:10 -0800 (PST) From: Joseph Strout <> Subject: neuron emulation, state of You can't get anything past Thomas, can you? :) It's true, the current state of the art in neuron emulation is crude at best. Here's where we are, at least as I can see it: 1. We can emulate a neuron's spike-generating function. That is, given the current at the spike initiation zone (usually the cell body), we can predict when the spikes will occur. NOT just the statistical properties of the spike train, but exactly when each and every spike will happen. This is usually done via kernel-based "black box" models, which can be configured in real time. That is, some folks have connected a neuron (via an electrode, of course) to a computer, and within minutes, the computer can predict the neuron's spikes as they happen. 2. We can reproduce most of the signal integration that occurs in the dendritic tree via compartmental modeling. This takes into account active ion channels, second messengers, and other good stuff which you might think is difficult to reproduce. It's not that difficult, in principle; it's just a big set of differential equations. The trouble, of course, is that the set can't be solved symbolically, and can only be approximated on a digital computer. So we approximate, and to get convergence (i.e., to keep the results close to the "correct" answer over extended periods of time), we use lots of compartments and very small time steps. It's a hideously slow process, but it does a fair job. 3. A few groups have started using analog VLSI to model neurons on microchips. To simplify their engineering, they strip away most or all of the dendritic properties listed as #2 above, and basically build a network of black boxes of the sort described in #1. But it's a start. These chips are very fast. Hmm, these are rather arbitrary distinctions, as there are a number of models that combine various levels. For example, many researchers look at small networks of neurons with simplified (but present) dendritic trees. Nobody has modelled more than a neuron or two in excrutiating detail, because the computation involved is overwhelming. But we're getting there! Cheers, -- Joe ,------------------------------------------------------------------. | Joseph J. Strout Department of Neuroscience, UCSD | | http://www-acs.ucsd.edu/~jstrout/ | `------------------------------------------------------------------' Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=7901