Summary of the Paper “What do brain data really show?” By Valerie G. Hardcastle and C. Matthew Stewart.

1. Introduction

In the paper, the authors try to show that the current approach of the neuroscientists to localize and modularize brain functions has no basis. This approach has been inspired from the study of body, where it is clear that it is composed of a very large number of parts, and that each part is highly specialized to perform a specific function in service of the survival and reproduction of the organism. Using the body as a model for the brain, neuroscientists guess that the brain, too, is composed of one or more functional parts, each of which is also specialized to facilitate the survival and reproduction of the organism. One by one, authors show that the techniques used by the neuroscientists are not compatible with the approach stated above. According to the authors, “… these are just prejudices, nothing more. And the underlying assumptions could very well be wrong” (Hardcastle, V and Stewart, C. M., pp. S73).


2. Localization and Single Cell Recordings

Neuroscientists study brain using single cell recordings, where they insert an electrode in or near a cell, and then record whether the activity of the cell changes when animal is stimulated in some way. If it does, then the degree of stimulus is changed and recordings are made. If it doesn’t, then the stimulus is changed or nearby cell is examined.

Authors point out that neuroscientists assume the brain to be a discrete system while making single cell recordings. Moreover, the maximum number of simultaneous recordings that they have done is around 150, which is very less compared the number of neurons in various brain areas. Based on the activity of the neurons, they try to make connections between cognitive tasks and the brain areas, which are also restricted by the fact that there are many different types of neurons, with different response properties and different interconnections with other cells.


3. Lesion Studies and the Assumption of Brain Constancy

By using the data from single cell recordings, neuroscientists estimate the behavior of certain brain areas and then they try to disrupt the hypothesized functions by placing lesions in otherwise normal animals.

These methods have serious technical difficulties. “By lesions studies are notorious for highly variable functional damage… A genuine replication of a lesion study in neurosciences is a practical impossibility” (Hardcastle, V and Stewart, C. M., pp. S76). Moreover, it is well known that any functional change in the nervous system leads to compensatory changes elsewhere. So the changes seen after the lesion is placed might be due to these compensatory changes.

Authors give an example of TMJ (Temporo-mandibular joint syndrome) to show that till now we don’t have a sketch of correct neuro-anatomy. TMJ is accompanied by ringing in the ear and till recent times it was not known that there was an auditory nerve that ran alongside the lower jaw. This makes the task of deriving the functions of brain areas, even more difficult.

4. Functional imaging to the rescue?

fMRI and other imaging techniques are the best known non-invasive recording devices currently available. Using these techniques we can observe the activity of the whole brain at the one time tied to some cognitive activity. But authors point out that these techniques have low spatial and temporal resolution. According to them, “…has a spatial resolution of 0.1mm and each scan samples about 5 secs” (Hardcastle, V and Stewart, C. M., pp. S77); whereas, the cell activity is about three to four orders of magnitude smaller and faster.

Moreover, the subtraction method used by experimenters to interpret the data, has an underlying assumption that two conditions under which experiment is conducted differ only in the cognitive task under consideration. This assumption is not necessarily true.

Lastly, the imaging techniques show the metabolic activity in the brain, so they ignore the components of cognition that may not require any changes in the metabolism.


5. Conclusion

Authors have been able to show that the simplifying assumptions of discreteness and constancy of function are not justified. Further, authors argue that the bias of neuroscientists to modularize brain data has no experimental backing; rather, it is just a prejudice. Therefore, the claims about functions are not correct as they assumed the local and specific functions prior to the gathering data for that claim.

References:

Hardcastle, V and Stewart, C. M. (2002), “What do brain data really show?”, Philosophy of science, 69, pp. S72-S82.