<p>Techniques that measure brain activity at a distance such as EEG and MEG measure spiking activity very poorly and indirectly. Instead, these techniques primarily measure <em>synaptic currents</em>.</p>

<p>Synaptic currents of course originate in some way from spiking activity, however:</p>

<ol>
<li><p>Synaptic currents may not occur in the vicinity of the spiking cells</p></li>
<li><p>The amplitude of synaptic currents depends on the current state of the cells impinged upon</p></li>
<li><p>Synaptic currents of different types in the same area can cancel each other out</p></li>
<li><p>Phase, polarity, and geometry can lead to a complex inverse problem at the sensor that has an infinite number of solutions.</p></li>
</ol>

<p>However, by making some rather strong assumptions, one can attempt to solve this inverse problem. Higher frequency EEG/MEG activity is more closely associated with spiking activity, and therefore most appropriate for attempting to localize spiking rather than other types of activity. See for example David and Friston 2003.</p>

<p>I'd also add that although the current agreement seems to be that EEG/MEG primarily come from synaptic currents, because synaptic currents do originate ultimately from some sort of spiking, EEG/MEG signals can correlate well with spiking activity measured with depth electrodes (for example Whittingstall &amp; Logothetis, 2009). It's just likely that the correlation is indirect, mediated through synaptic potentials.</p>

<hr>

<p>Buzsáki, G., Anastassiou, C. A., &amp; Koch, C. (2012). The origin of extracellular fields and currents—EEG, ECoG, LFP and spikes. Nature reviews neuroscience, 13(6), 407.</p>

<p>David, O., &amp; Friston, K. J. (2003). A neural mass model for MEG/EEG:: coupling and neuronal dynamics. NeuroImage, 20(3), 1743-1755.</p>

<p>Whittingstall, K., &amp; Logothetis, N. K. (2009). Frequency-band coupling in surface EEG reflects spiking activity in monkey visual cortex. Neuron, 64(2), 281-289.</p>

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2018-08-01T16:49:20.177Z
2018-08-01T16:58:28.130Z
2018-08-01T16:58:28.130Z
Bryan Krause
<p>Given MEG is an approximation of neuronal spiking, are there any models that associate the spiking of simulated neurons to an MEG signal? Ideally, this would be a model with some amount of behaviour (mapping to an output, such as a motor action), but purely biological models are fine too.</p>

CC BY-SA 4.0
2018-08-01T12:26:21.687Z
*Ideally, this would be a model with some amount of behavior*? What kind of behavior? Neuronal behavior? If you mean behavior at the psychological level than single neuron activity is hard and next to impossible to couple to behavior, let alone in a simulation! What do you want to know? Quite frankly I don't understand the question.
AliceD
CC BY-SA 4.0
2018-08-01T13:12:49.123Z
it's not clear to me either, but maybe by "behavior" you mean something very simple so https://www.sciencedirect.com/science/article/pii/S0896627313009203 might be of interest
got trolled too much this week
CC BY-SA 4.0
2018-08-01T16:37:16.940Z
*"Given MEG is an approximation of neuronal spiking"* - I don't agree with this statement as a given. See for example https://www.nature.com/articles/nrn3241 (although they don't discuss MEG, most of the discussion of EEG there will also apply to MEG). If you are talking about seizures rather than normal brain activity, that's a bit different, though.
Bryan Krause
CC BY-SA 4.0
2018-08-01T16:46:44.850Z
@BryanKrause you're absolutely right. Research I'm doing to answer this question is pointing me in the direction that MEG is the sum of post-synaptic potentials. Due to a modeling bias I have, I often think of post-synaptic potentials as equivalent to spiking.
Seanny123
CC BY-SA 4.0
2018-08-01T16:50:33.550Z
@Seanny123 I made my comment into a brief answer; I could go in more depth but I think it would get a bit lengthy. I highly recommend that Buzsaki paper and in general reading across the EEG literature. Certainly EEG and MEG are different but I think in this context the arguments are nearly identical.
Bryan Krause
CC BY-SA 4.0
2018-08-01T16:52:12.663Z
I'd also add that although the current agreement seems to be that EEG/MEG primarily come from synaptic currents, your modeling bias that post-synaptic potentials are equivalent to spiking is also somewhat supported, and there are several papers showing that indeed, those EEG/MEG signals do correlate well with spiking activity measured with depth electrodes. It's just likely that the correlation is indirect, mediated through synaptic potentials.
Bryan Krause
CC BY-SA 4.0
2018-08-01T16:53:34.147Z
Whittingstall, K., & Logothetis, N. K. (2009). Frequency-band coupling in surface EEG reflects spiking activity in monkey visual cortex. Neuron, 64(2), 281-289. for example
Bryan Krause
<reference-request><theoretical-neuroscience><meg>
MEG from simulated neurons
Seanny123
# MEG from simulated neurons

(Asked by: username_0 on 2018-08-01)

Given MEG is an approximation of neuronal spiking, are there any models that associate the spiking of simulated neurons to an MEG signal? Ideally, this would be a model with some amount of behaviour (mapping to an output, such as a motor action), but purely biological models are fine too.

**Tags:** reference-request, theoretical-neuroscience, meg

> **Comments:**
> **username_1**: *Ideally, this would be a model with some amount of behavior*? What kind of behavior? Neuronal behavior? If you mean behavior at the psychological level than single neuron activity is hard and next to impossible to couple to behavior, let alone in a simulation! What do you want to know? Quite frankly I don't understand the question.  
> **username_2**: it's not clear to me either, but maybe by "behavior" you mean something very simple so https://www.sciencedirect.com/science/article/pii/S0896627313009203 might be of interest  
> **username_3**: *"Given MEG is an approximation of neuronal spiking"* - I don't agree with this statement as a given. See for example https://www.nature.com/articles/nrn3241 (although they don't discuss MEG, most of the discussion of EEG there will also apply to MEG). If you are talking about seizures rather than normal brain activity, that's a bit different, though.  
> **username_0**: @BryanKrause you're absolutely right. Research I'm doing to answer this question is pointing me in the direction that MEG is the sum of post-synaptic potentials. Due to a modeling bias I have, I often think of post-synaptic potentials as equivalent to spiking.  
> **username_3**: @username_0 I made my comment into a brief answer; I could go in more depth but I think it would get a bit lengthy. I highly recommend that Buzsaki paper and in general reading across the EEG literature. Certainly EEG and MEG are different but I think in this context the arguments are nearly identical.  
> **username_3**: I'd also add that although the current agreement seems to be that EEG/MEG primarily come from synaptic currents, your modeling bias that post-synaptic potentials are equivalent to spiking is also somewhat supported, and there are several papers showing that indeed, those EEG/MEG signals do correlate well with spiking activity measured with depth electrodes. It's just likely that the correlation is indirect, mediated through synaptic potentials.  
> **username_3**: Whittingstall, K., & Logothetis, N. K. (2009). Frequency-band coupling in surface EEG reflects spiking activity in monkey visual cortex. Neuron, 64(2), 281-289. for example  

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## 1 answers

### Answer by username_3 on 2018-08-01. Score: 4 | Accepted answer

Techniques that measure brain activity at a distance such as EEG and MEG measure spiking activity very poorly and indirectly. Instead, these techniques primarily measure *synaptic currents*.

Synaptic currents of course originate in some way from spiking activity, however:

1. Synaptic currents may not occur in the vicinity of the spiking cells
2. The amplitude of synaptic currents depends on the current state of the cells impinged upon
3. Synaptic currents of different types in the same area can cancel each other out
4. Phase, polarity, and geometry can lead to a complex inverse problem at the sensor that has an infinite number of solutions.

However, by making some rather strong assumptions, one can attempt to solve this inverse problem. Higher frequency EEG/MEG activity is more closely associated with spiking activity, and therefore most appropriate for attempting to localize spiking rather than other types of activity. See for example David and Friston 2003.

I'd also add that although the current agreement seems to be that EEG/MEG primarily come from synaptic currents, because synaptic currents do originate ultimately from some sort of spiking, EEG/MEG signals can correlate well with spiking activity measured with depth electrodes (for example Whittingstall & Logothetis, 2009). It's just likely that the correlation is indirect, mediated through synaptic potentials.

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Buzsáki, G., Anastassiou, C. A., & Koch, C. (2012). The origin of extracellular fields and currents—EEG, ECoG, LFP and spikes. Nature reviews neuroscience, 13(6), 407.

David, O., & Friston, K. J. (2003). A neural mass model for MEG/EEG:: coupling and neuronal dynamics. NeuroImage, 20(3), 1743-1755.

Whittingstall, K., & Logothetis, N. K. (2009). Frequency-band coupling in surface EEG reflects spiking activity in monkey visual cortex. Neuron, 64(2), 281-289.


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