Yehouda Harpaz
yh@maldoo.com
last updated 3 Dec 2007
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Progress in understanding of how the brain works

Most of the discussion in this site of current research are highly critical (Errors, Myths). This page is intended to highlight what looks to me like progress.

1. The brain is always active

1.1) In my model I wrote as one of the major hypotheses that the System (i.e. the brain) is always active (Major Hypothseis 6, 4.5.3). I also wrote that it looks to me obvious (6.3.2.6).

1.2) At least 99% of published articles in the area are effectively based on the assumption that the activity of the brain when it does not explicitly do something is of no interest. However, this seems to change. For example, in this article (Spontaneous Activity Associated with Primary Visual Cortex: A Resting-State fMRI Study, Wang et al, Cerebral Cortex Advance Access published online on June 29, 2007 ; Full text here) they look at activity of the resting brain, and say that "This confirmation supports the perspective that brain is a system intrinsically operating on its own, and sensory information interacts with rather than determines the operation of the system."

1.3) A much stronger support to their conclusion is the observation that the activity of the "resting brain" is far larger than the changes that are normally reported, which they discuss in the paragraph following the abstract. As the references that they mention (one from 1955) show, that is an old fact. What is progress is the fact that they are actually looking at a resting brain, and interpret it as ".. operating on its own..".

1.4) They (and apparently the papers by Raichle that they quote) are still worried of "going too far". They say "Therefore, as suggested by Raichle and colleagues, in terms of overall brain functions, the ongoing intrinsic activity within various brain systems may be at least as important as the activity evoked by external stimuli (Raichle and Gusnard 2005; Raichle and Mintun 2006)." Thus the intrinsic activity is only ".. at least as important..", rather than the obvious "much more important", so we still have some distance to go. But there is a progress in the right direction.

2. Do neurons "represent" anything?

In this article (Churchland MM, Shenoy KV (2007) Temporal complexity and heterogeneity of single-neuron activity in premotor and motor cortex. Journal of Neurophysiology. 97:4235-4257doi ), they find that the neurons in the premotor and motor cortex show complex and heterogenous activity. From this, they suggest the possibility that these neurons don't represent anything.

As discussed here, neurons don't represent anything, but many cognitive scientists and neurosceintists seem to be unable to comprehend this possibility. The authors of the article above are clrearly capable to comprehending it. They present alternative view, but seem to regard their observations as showing that the neurons that they look at do not represent anything. They present the same view in other articles (list of publications, for example the one about "Reference frames for reach planning in macaque dorsal premotor cortex").

The fact that they positively think that the neurons do not represent is progress. The progress is limited, however, because it is still based on the assumption that showing correlation between neural activity and something else (behaviour, stimulus) shows representation. Therefore "representationalists" can still believe that these neurons represent something else.

3. looking at ensembles of neurons.

In this article (Natural stimuli evoke dynamic sequences of states in sensory cortical ensembles, Jones et al, PNAS | November 20, 2007 | vol. 104 | no. 47 | 18772-18777 (open accesss article)), they analyze ensembles of neurons, and show that the ensemble response correlates much better with the input than single-neuron analysis. They stress that the single-neuron analysis that is normally used loses information.

Their data is about taste in rats, and it is not obvious how it is going to generalize to other senses. The number of neurons in each "ensemble" is also pretty small (10). But it is encouraging to see researchers that look at ensembles, and explicitly state that single-neuron analysis loses information. They explicitly state that the coherent state sequences that they see do not represent sensory codes, which is also progress.