The first electroencephalogram (EEG) was made about eighty years ago. Ever since, due to its non-invasive basis, it has been one of the most used instruments to analyse the brain activity. However, it is still unknown which processes in the brain are represented in the EEG and which are not. Let’s go even a step further: how sure are we EEGs really tell us something?

Creutzfeldt and his colleagues were one of the first to show that the major part of the EEG signal consists of excitatory and inhibitory postsynaptic potentials (Creutzfeld et al., 1966). However, they also found that a certain part of the EEG is based on processes that have nothing to do with brain or even cellular activity. Even, for instance, blinking your eyes or even just moving them, gives a signal that is out of proportion to such an extent that it ruins the whole EEG. Is it possible to make a distinction between these signals in order to find the activity that really matters?

It had not been until 2009, when a group of researchers tried to make a correlation between surface EEG and the scalp’s underlying neural activity (Whittingstall & Logothetis, 2009). This, they achieved by using a kind of mini-EEGs (actually they are listed as MUA and LFT, but let’s try to keep it somewhat comprehensible). These electrodes however, as distinct from the EEG (where they are placed on the scalp), were placed on the neurons directly.

In monkeys, they analysed the different data sets after showing them different movies with footage of everyday life. You know, bananas and so on. And indeed, the striking result was that a high neuron firing rate correlated to high EEG levels.

Well, ‘nothing new’, you would say. ‘That’s pretty obvious’. Yes, as obvious as things seem, they do need to be proven first really to be obvious. But this was not their only goal. Their goal was to find a way of deducing real neural activity from the raw EEG in order to find a sound image. And perhaps this crucial tool is is now being found.

Works listed:

Whittingstall, K & Logothetis, N. Frequency-Band Coupling in Surface EEG Reflects Spiking Activity in Monkey Visual Cortex. Neuron 64, 281-299. October 29, 2009. Elsevier Inc.

Creutzfeldt, O.D., Watanabe, S., and Lux, H.F. Relations between EEG pehomena and potentials of single cortical cells. Electroencephalogr. Clin. Neurophysiol. 20, 1-18. 1966.