Intracranial EEG power spectra and phase synchrony during consciousness and unconsciousness.

Power density spectra and phase synchrony measurements were taken from intracranial electrode grids implanted in epileptic subjects. Comparisons were made between data from the waking state and from the period of unconsciousness immediately following a generalised tonic-clonic seizure. Power spectra in the waking state resembled coloured noise. Power spectra in the unconscious state resembled coloured noise from 1 to about 5 Hz, but at higher frequencies changed in two out of three subjects to resemble white noise. This boosted unconscious gamma power to a higher level than conscious gamma power. For both gamma and beta passbands, synchrony measurements showed more widespread phase synchrony in the unconscious than the conscious state. We conclude that neither gamma activity per se nor phase synchrony per se are neural correlates of consciousness.

Public health and the radio frequency radiation emitted by cellphone technology, smart meters and WiFi.

This paper argues that the prevailing official narrative in New Zealand concerning the relationship between public health and the radio frequency emissions (RF) from cellphone technology, WiFi and electricity smart meters is scientifically and ethically flawed. The main regulatory document in the area, NZS2772.1:1999, is 20 years out of date and ignores existing laboratory evidence disproving its core assumption that the only biological effect of non-ionising radiation is tissue heating. This and further laboratory evidence for harmful effects of RF continues to be ignored, nominally on the contradictory grounds that (a) cellphone manufacturers say their products now emit less RF than early models, so early lab studies exposed tissue to RF levels higher than those now relevant (b) given the lack of actual data on population exposures either then or now, all laboratory evidence is unconvincing anyway. The offical narrative further opines that since there exist both laboratory and epidemiological studies concluding that RF is not biologically harmful, as well as studies concluding that RF is harmful, the appropriate response is to count up the number on each side, declare the "weight of evidence" to be such that "causation is not proven" and, pending unspecified further studies, continue exposing to unmonitored levels of RF the entire population of the country, none of whom has given informed consent to participate in the experiment. This approach is obviously unethical. It is also unacceptable scientifically. First, the algebraic model is flawed: studies that do find a harmful effect of RF are not invalidated by differently constructed studies that fail to find an effect. Secondly, while causation is relatively easy to study in the laboratory, it is difficult if not impossible to prove epidemiologically, given that (1) the very narrative under discussion has ensured that there is now no unexposed control group and (2) interpretation of timeline correlation studies is hampered by changes in the way new cancer registrations have been recorded over the years and the perennial problem of multiple possible causal factors. The present paper concludes that a precautionary approach is justified, and ends with a number of specific suggestions on how to start implementing such an approach.

Auditory click stimuli evoke event-related potentials in the visual cortex.

The objective of this study was to determine whether unimodal auditory stimuli evoke event-related potentials (ERPs) in brain areas normally designated as the visual cortex (VC). The topographical distribution of ERPs evoked by auditory click stimuli was measured from (a) electroencephalographic electrodes on the scalp of six neurologically normal adult human participants and (b) intracranial electrodes implanted on the cortex of one epileptic adult human participant. In all participants, unimodal click stimuli evoked ERPs over both the auditory cortex (AC) and the VC. Relative amplitudes of ERPs at different scalp electrodes did not support the idea that the ERPs over VC were volume-conducted versions of those over AC, and intracranial records confirmed the origin of some click-evoked ERPs in both V1 and other regions of VC. We conclude that unimodal auditory stimuli can evoke ERPs in VC. This finding adds to the earlier evidence for the effect of visual stimuli on AC by providing new evidence for bidirectional functional connectivity in the audio-visual network of the human brain. The implication is that not only do visual stimuli affect hearing; auditory stimuli also affect visual perception.

A possible physiological basis for the discontinuity of consciousness.

A comparison is made between the frequency of local minima in the analytic power (AP) of intracranial EEG (ECoG) from waking and unconscious human subjects and the frequency of putative frames of consciousness reported in earlier psychological literature. In ECoG from unconscious subjects, the frequency of deep minima in AP is found to be a linear function of bandwidth. In contrast, in ECoG from conscious subjects, the bandwidth/minima-frequency curve saturates or plateaus at minima frequencies similar to the frequencies of previously reported frames of consciousness. This result is consistent with the hypothesis that local minima in AP may act as the shutter in a cinematographic model of consciousness. The fact that artificially generated samples of black noise with power spectra similar to ECoG data give similar results in the analyses above suggests that the discontinuous nature of consciousness is not due to some specifically biological factor, but is simply a consequence of the physical properties of the 1/f (aka power law) oscillations that are widely found in nature.

A method to study global spatial patterns related to sensory perception in scalp EEG.

Prior studies of multichannel ECoG from animals showed that beta and gamma oscillations carried perceptual information in both local and global spatial patterns of amplitude modulation, when the subjects were trained to discriminate conditioned stimuli (CS). Here the hypothesis was tested that similar patterns could be found in the scalp EEG human subjects trained to discriminate simultaneous visual-auditory CS. Signals were continuously recorded from 64 equispaced scalp electrodes and band-pass filtered. The Hilbert transform gave the analytic phase, which segmented the EEG into temporal frames, and the analytic amplitude, which expressed the pattern in each frame as a feature vector. Methods applied to the ECoG were adapted to the EEG for systematic search of the beta-gamma spectrum, the time period after CS onset, and the scalp surface to locate patterns that could be classified with respect to type of CS. Spatial patterns of EEG amplitude modulation were found from all subjects that could be classified with respect to stimulus combination type significantly above chance levels. The patterns were found in the beta range (15-22 Hz) but not in the gamma range. They occurred in three short bursts following CS onset. They were non-local, occupying the entire array. Our results suggest that the scalp EEG can yield information about the timing of episodically synchronized brain activity in higher cognitive function, so that future studies in brain-computer interfacing can be better focused. Our methods may be most valuable for analyzing data from dense arrays with very high spatial and temporal sampling rates.

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.

The concept of free will: philosophy, neuroscience and the law.

Various philosophical definitions of free will are first considered. The compatibilist definition, which says simply that acts are freely willed if they are not subject to constraints, is identified as much used in the legal system and essentially impervious to scientific investigation. A middle-ground "incompatibilist" definition, which requires that freely willed acts be consciously initiated, is shown to be relevant to the idea of mens rea and in the author's view not actually incompatible in principle with a fully scientific worldview. Only the strong libertarian definition, which requires that freely willed acts have no physical antecedents whatsoever, makes the existence of free will very hard to swallow scientifically. However, with regard to the middle-ground "incompatibilist" definition, three different lines of scientific experimental evidence are then described, which suggest that, in fact, consciousness is not the real cause of much of what is generally considered as voluntary behavior. Many voluntary actions are initiated preconsciously, with consciousness kept informed only after the neural events leading to the act have begun. It is suggested that a reasonable way of integrating these experimental findings with the idea that persons do have a somewhat more than compatibilist version of free will is to acknowledge explicitly that a person is a mixture of conscious and unconscious components. In this scenario, the mind in mens rea would have to be judged guilty if it contained either conscious or unconscious intentions to perform the guilty act.

The rotating spot method of timing subjective events.

The rotating spot method of timing subjective events involves the subject's watching a rotating spot on a computer and reporting the position of the spot at the instant when the subjective event of interest occurs. We conducted an experiment to investigate factors that may impact on the results produced by this method, using the subject's perception of when they made a simple finger movement as the subjective event to be timed. Seven aspects of the rotating spot method were investigated, using a factorial experiment. Four of these aspects altered the physical characteristics of the computer generated spot or clock face and the remaining three altered the instructions given to the participant. We found compelling evidence that one factor, whether the subject was instructed to report the instant when the finger movement was initiated or the instant when it was completed, resulted in a systematic shift in the response. Evidence that three other factors affect the observed variability in the response was also found. In addition, we observed that there are substantial systematic differences in the responses made by different subjects. We discuss the implications of our findings and make recommendations about the optimal way of conducting future experiments using the rotating spot method. Our overall conclusion is that our results strongly validate the rotating spot method of timing at least the studied variety of subjective event.

Topography, independent component analysis and dipole source analysis of movement related potentials.

The objective of this study was to test, in single subjects, the hypothesis that the signs of voluntary movement-related neural activity would first appear in the prefrontal region, then move to both the medial frontal and posterior parietal regions, progress to the medial primary motor area, lateralize to the contralateral primary motor area and finally involve the cerebellum (where feedback-initiated error signals are computed). Six subjects performed voluntary finger movements while DC coupled EEG was recorded from 64 scalp electrodes. Event-related potentials (ERPs) averaged on the movements were analysed both before and after independent component analysis (ICA) combined with dipole source analysis (DSA) of the independent components. Both a simple topographic analysis of undecomposed ERPs and the ICA/DSA analysis suggested that the original hypothesis was inadequate. The major departure from its predictions was that, while activity over many brain regions did appear at the expected times, it also appeared at unexpected times. Overall, the results suggest that the neuroscientific 'standard model', in which neural activity occurs sequentially in a series of discrete local areas each specialized for a particular function, may reflect the true situation less well than models in which large areas of brain shift simultaneously into and out of common activity states.

Spatial resolution and the neural correlates of sensory experience.

Freeman and Baird [5; Freeman WJ, Baird B. Behav Neurosci 1987;101:393-408] recorded from the surface of the brain in waking rabbits and found spatial patterns of voltage that covaried with sensory experience. We simulate mathematically the electric fields produced by radial dipoles in cortical gyri and show that patterns with the spatial frequencies observed by Freeman and Baird could be produced by cortical dipoles spaced 3 mm apart. We further calculate that to resolve the patterns produced by such dipole arrays, it is necessary to record less than 2.5 mm above the surface of the cortex. High-pass spatial filters increase this distance to 4.5 mm. Since the human scalp is 15-16 mm above the brain, we conclude that spatial patterns of voltage covarying with sensation are unlikely to be detectable in scalp records. If such patterns do exist in humans, dural or sub-dural electrode arrays, with an inter-electrode spacing of 1 mm or less, will be necessary to record them.

The great subjective back-referral debate: do neural responses increase during a train of stimuli?

Evidence is summarised for and against the hypothesis that potentiation or facilitation of neural responses during a train of threshold-level stimuli occurred in the experiments reported by . It is concluded that such potentiation probably did occur. Since the main arguments for the existence of subjective backwards referral () take it as given that such potentiation did not occur, it is further concluded that the main arguments for the existence of subjective backwards referral fail.