The sometimes pernicious role of theory in science

Neurophysiology of functional imaging

The successes of PET and fMRI in non-invasively localizing sensory functions had encouraged efforts to transform the subjective concepts of cognitive psychology into objective physical measures. The assumption was that mental functions could be decomposed into non-overlapping, context-independent modules that are operated on by separable areas of a computer-like brain. The failures of cognitive modularity and of a very localized phrenology are generally, but not universally, accepted; but in their place, and usually not distinguished from the original revolutionary hopes of clarification, experimental results are being interpreted in terms of rather flexible definitions of both cognitive concepts and the degree of localization. In an alternative approach, we have connected fMRI, (13)C MRS, and electrophysiology measurements of brain energy to connect with observable properties of mental life (i.e., awareness). We illustrate this approach with a sensory stimulation experiment; the degree of localization found in BOLD signals was related to the global energy of the brain which, when manipulated by anesthetics, affected the degree of awareness. The influence of brain energy upon functional imaging maps is changing the interpretations of neuroimaging experiments, from psychological concepts generating computer-like responses to empirical responses dominated by the high brain energy and signaling at rest. In our view "baseline" is an operational term, an adjective that defines a property of a state of the system before it is perturbed by a stimulus. Given the dependence of observable psychological properties upon the "baseline" energy, we believe that it is unnecessarily limiting to define a particular state as the baseline.

EEG synchrony during a perceptual-cognitive task: widespread phase synchrony at all frequencies

OBJECTIVES

(1) To examine the validity of comparing the phase of broad-band signals. (2) To measure phase synchrony over the whole head, at a variety of frequencies.

METHODS

The concept of broad band phase is investigated (a) by visual comparison of the time series of two channels of filtered data with the time series of the spatial analytic phase difference (SAPD) between the two channels and (b) using artificial sinusoids. Phase synchrony is then measured in 64-channel EEG recorded while human subjects performed a perceptual-cognitive task, by calculation of analytic phase differences between each channel and a frontal synchrony reference channel. The number of channels in synchrony with the reference channel at a series of frequency passbands is compared for data acquired using a common recording reference, the same data re-referenced to an average reference and artificial noise.

RESULTS

Analytic phase is shown to represent the resultant of the phasor angles of all the narrow band signals incorporated in a composite waveform. Episodic global phase synchrony is identified in background EEG, in all passbands from theta to epsilon. Many of the episodes of widespread synchrony occur in both common-referenced and average-referenced data, but some common-reference episodes are not seen in average-referenced data. In both forms of data, synchrony is about equally widespread in all subjects at lower passbands, but more widespread in some subjects than others at higher passbands.

CONCLUSIONS

(1) It is valid to measure the analytic phase of broad band EEG signals. (2) Non-local phase synchrony is intermittently present in all frequency bands from theta to epsilon, not only during and after external stimuli, but also in background EEG. (3) In some subjects synchrony is more widespread in gamma and epsilon bands than in beta, alpha or delta bands, but in others the reverse is true. (4) Some of the episodes of synchrony seen in common referenced data may be artifacts of a sudden decrease in power at the recording electrodes in comparison with the common reference electrode. However, most of the episodes of synchrony in common-referenced data cannot be explained in this fashion. (5) Episodes of widespread synchrony are not established instantaneously. During the establishment of most episodes of '40 Hz' synchrony, the number of channels in synchrony peaks after about 100 ms.

SIGNIFICANCE

If long-range phase synchrony really is a hallmark of consciousness, it should be present most of the time the subject is conscious. Our results confirm this prediction, and suggest that consciousness may involve not only gamma frequencies, but the whole range from theta to epsilon. The mechanism of synchrony establishment at the scalp as shown by the present method is relatively slow and thus more likely to involve chemical synapses than gap junctions, electric fields or quantum non-locality.

In pursuit of knowledge

This article is based on the proposition that to understand the nature of knowledge, and how best to acquire it, one must look first at how the brain abstracts knowledge from the information provided by sensory receptors. The nature of this biological process of knowledge acquisition is suggested by the necessary conditions for the occurrence of learning, and from consideration of these necessary conditions in terms of what is currently known about the properties and limitations of neural systems. This entails discussion of an important distinction that must be made between "perceptual" and "associative" learning and between the neural systems required to mediate these two kinds of learning. There is also discussion of the manner in which language can overcome the limitations of neurological systems to greatly extend the scope of associative learning. This leads on to discussion of the role of active efferent language systems and temporary memory in the mediation of thinking. Consideration of the main features of the biological process of knowledge acquisition confirms, and extends to perception, Hume's famous conclusion that knowledge derives from the similarity or temporal contiguity of recurring events. New insights are also obtained concerning the biological causes of bias in the knowledge acquisition process, concerning the intellectual process of theory generation, and concerning the role of theory in the conduct of empirical research. Finally, and most importantly, it can be concluded that all knowledge is theory and hence that the ultimate goal of science is the development of better theories.