A New Electroencephalogram Associated With Thinking

Electroencephalographic Differences between Resting and Mental Multiplication

The average frequency of 30 sec. of EEG tracing for two states, resting and mental multiplication (thinking), was determined for 20 Ss by counting each visually detectable change in pen deflection regardless of amplitude. (1) Thinking gave higher average activity scores than resting. (2) The difference in average activity between thinking and resting was greatest in the two frontal and left temporal areas and it was significantly different from the differences in the other areas. (3) In the resting state there was a difference between left and right frontal and temporal areas (which increased while thinking) in contrast with a left-right symmetry of the other areas tested. These findings were interpreted as representing characteristic average activity for the areas and condiions tested and were offered as evidence for the differential utilization of brain areas in the given tasks.

Pitfalls in the dipolar model for the neocortical EEG sources

For about six decades, primary current sources of the electroencephalogram (EEG) have been assumed dipolar in nature. In this study, we used electrophysiological recordings from anesthetized Wistar rats undergoing repeated whisker deflections to revise the biophysical foundations of the EEG dipolar model. In a first experiment, we performed three-dimensional recordings of extracellular potentials from a large portion of the barrel field to estimate intracortical multipolar moments generated either by single spiking neurons (i.e., pyramidal cells, PC; spiny stellate cells, SS) or by populations of them while experiencing synchronized postsynaptic potentials. As expected, backpropagating spikes along PC dendrites caused dipolar field components larger in the direction perpendicular to the cortical surface (49.7 ± 22.0 nA·mm). In agreement with the fact that SS cells have “close-field” configurations, their dipolar moment at any direction was negligible. Surprisingly, monopolar field components were detectable both at the level of single units (i.e., −11.7 ± 3.4 nA for PC) and at the mesoscopic level of mixed neuronal populations receiving extended synaptic inputs within either a cortical column (−0.44 ± 0.20 μA) or a 2.5-m3-voxel volume (−3.32 ± 1.20 μA). To evaluate the relationship between the macroscopically defined EEG equivalent dipole and the mesoscopic intracortical multipolar moments, we performed concurrent recordings of high-resolution skull EEG and laminar local field potentials. From this second experiment, we estimated the time-varying EEG equivalent dipole for the entire barrel field using either a multiple dipole fitting or a distributed type of EEG inverse solution. We demonstrated that mesoscopic multipolar components are altogether absorbed by any equivalent dipole in both types of inverse solutions. We conclude that the primary current sources of the EEG in the neocortex of rodents are not precisely represented by a single equivalent dipole and that the existence of monopolar components must be also considered at the mesoscopic level.

Recording the brain at work: the visible, the readable, and the invisible in electroencephalography

The electroencephalogram (EEG), the graphic recording of the electric activity of the human brain, kindled far-reaching speculations about the imminent deciphering of mind and brain in the 1930s. Regardless of the thousands of neurons in the human cortex, recording from a person at rest produced a surprisingly regular line oscillating at 10 per second that disappeared at the moment of mental activity. With ever more groups specializing in electroencephalography, however, the deciphering of mind and brain did not materialize but moved further away in the information produced. In the various approaches employed in EEG research, such as the analysis of the graphic code, the search for pathognomic patterns or the imaging of cognitive processing, visualization guided research as well as theorizing, its productivity continued to keep the epistemological question open.

Issues relating to the subtraction phase in EOG artefact correction of the EEG

An important method for removing the effect of ocular artefact from the EEG is 'EOG correction'. This method estimates the proportion of ocular artefact that is in the EEG, and removes it by subtraction. To date, EOG correction research has focused on problems relating to the estimation of the correction coefficients. Using both mathematical rationale and empirical data, this paper addresses issues relating to the subtraction phase, such as the magnitude of error that can be expected due to EOG correction. Using ERP methodology, principal component and regression analyses, it is shown that the N1P2 complex propagates forward to the horizontal and radial (but not vertical) electrooculograms (EOG), and it is shown mathematically that this will result in EOG-correction error. Assuming an accurate estimate of ocular contamination of the EEG, maximal subtraction-phase error of the N1P2 complex was found to be a prefrontal attenuation of 15-22%, decreasing to central and occipital enhancements of 3-4% and 13-14%, respectively. The magnitude of this subtraction-phase error is compared to between-subject ERP variability and to error associated with EOG rejection (omitting data contaminated by ocular artefact). It is argued that such EOG correction error is small relative to both artefact rejection procedures and to normal variability found in ERP studies, and that it is less pernicious than artefact rejection procedures.

On the intercorrelation of some frequency and amplitude parameters of the human EEG and its functional significance. Communication. I: Multidimensional neurodynamic organization of functional states of the brain during intellectual, perceptive and motor activity in normal subjects

In 95 normal subjects, a separate evaluation of the amplitude and frequency parameters of EEG by period analysis made it possible to reveal, using factor analysis, four independent groups of parameters--the EEG factors, two of which being independent of the amplitude fluctuations. They were considered as integral EEG characteristics of qualitatively different neurophysiological processes. Decrease of Factor I values during mental activity (called 'general activation') reflected an intercorrelated desynchronization of the wave amplitudes in all the bands, a decrease of alpha-index (percentage presence in epoch) and regularity together with parallel increase of the indices and mean periods of delta- and theta-waves. This generalized reaction has shown 'non-specific' dependence upon novelty and difficulty of the tasks and stimuli with certain task-specific topographical distribution. An increase of values of regional Factor Ia in the anterior areas was caused by delta- and theta-amplitude synchronization, more pronounced during matching the rhymes (MR) than in mental multiplication (MM). An increase of Factor II values (related to increase of the index, frequency and regularity of beta-activity and called 'cortical excitation', CE) was more expressed during MR, whereas an increase of Factor III values (an increase of mean alpha-period and theta-index called 'active selective inhibition', ASI) was characteristic of MM, the latter reaction being evident in the right hemisphere. During analysis of external sound stimuli and rhythmical clenching of a fist, an increase of Factor III values was accompanied by decrease of Factor II values [corrected]; in the motor activity, such reciprocal reaction being localized in the central areas contralateral to the hand moved . Neuropsychological analysis suggests that CE correlates with associative and successively organized mental operations involving search for memory traces and ASI presumably relates to different aspects of mental selectivity such as simultaneous mental operations, voluntary attention and mental automation, the latter two cases being supported by parallel reduction of CE.

Differential responses to mental stress in high and low anxious normal humans assessed by frontal midline theta activity

The distinct EEG theta rhythm from the frontal midline area observed during performance of mental tasks has been called Fm theta. In the present study, plasma catecholamine responses to mental stress were investigated using male students with (n = 12) and without (n = 12) Fm theta. The subjects were requested to complete the trait anxiety scale of STAI, and control blood samples were obtained. 65 min later, their EEGs were recorded during performance of an arithmetic addition task for 5 min. The state anxiety scores of STAI were obtained twice before and after the EEG recording. Blood samples were drawn three times during the state anxiety test and the EEG recording. The Fm theta appearance group showed low trait anxiety and a decrease of state anxiety after the mental task; however, the Fm theta non-appearance group exhibited high trait anxiety and no changes of state anxiety before and after the mental task. The concentrations of DA, HVA, NA and MHPG in the Fm theta appearance group showed lower levels at all times compared to those in the non-appearance group. In the Fm theta appearance group, an increase of DA turnover was observed by the addition of mental task. On the other hand, the Fm theta non-appearance group showed an increase of NA turnover.

Alpha-like EEG activity in non-REM sleep and the fibromyalgia (fibrositis) syndrome

The occurrence and characteristics of alpha-like activity during non-REM (NREM) sleep were examined in 11 subjects suffering from non-inflammatory (non-rheumatoid) musculoskeletal pain--fibromyalgia ('fibrositis'), and in 15 symptom-free controls. Both groups claimed to be good sleepers. Mean percentage alpha-like activity in sleep stages 2, 3, 4 and for NREM as a whole were greatest for the fibromyalgia group, but not significantly different from those of the controls. Overlap in the distribution of NREM alpha-like activity in sleep between the two groups indicated that it is not directly related to musculoskeletal symptoms. Spectral analyses showed a frontal area prevalence of this (kappa?) activity in the fibromyalgia group.

Alpha-like rhythmical activity of the temporal lobe

In addition to the classical posterior alpha rhythm and Rolandic mu rhythm, a third type of rhythmical activity in alpha- (or sub-alpha-) frequency can be recorded over the temporal lobe and especially over the midtemporal region. This rhythm usually escapes detection in the scalp EEG but is commonly seen over bone defects ("breach rhythm"). With the use of epidural electrodes, however, this rhythm becomes quite prominent and dominates the activity of the temporal lobe unless there is excessive local EEG abnormality and/or pathology. This temporal rhythm lies in the range of 6-11/sec and thus often extends into the theta frequency range. There is no proven blocking effect; this mere fact sets it apart from posterior alpha and Rolandic mu rhythm. It is essentially a rhythm of the waking state but may linger into drowsiness and even into light NREM sleep. It is also separable from the highly controversial frontotemporal "kappa rhythm" of bygone times. EEG recordings from the depth of the temporal lobe (limbic structures) do not demonstrate such a rhythm that is likely to originate from the neocortical portion. Its neurophysiological and psychophysiological significance is enigmatic.

Neural mechanisms distinguishing the neocortical EEG of C57BL/6 mice from that of DBA/2 mice

C57BL/6 inbred mice lack the 1-5 sec bursts of 6-7 cps spindles characteristic of the neocortical EEG of DBA/2 mice during waking. C57BL/6 mice (1) may be unable to generate any synchronized cortical EEG activity, (2) may lack the thalamocortical circuitry required to generate these brief spindle episodes (BSEs), (3) may lack mechanisms that can activate this circuitry or (4) may possess a potent mechanism to suppress BSE initiation and generation. Possibilities 1 and 2 have been eliminated because C57BL/6 mice generate pentobarbital, rostropontine-induced and sleep spindles, and because certain C57BL/6 sleep spindles resembled the BSEs seen in DBA/2 mice. Possibilities 3 and 4 were examined in the experiments reported here. In DBA/2 mice, pentylenetetrazol activates BSEs at subconvulsant doses. In contrast, neither 20 nor 50 mg/kg, IP, pentylenetetrazol activated BSEs in C57BL/6 mice, although the higher dose provoked 4-5 cps slow waves and myoclonic jerks. In DBA/2 mice, the beta-noradrenergic antagonist propranolol has been reported to powerfully release BSEs. In C57BL/6 mice, 10 and 15 mg/kg propanolol weakly released BSEs; fewer than 3 per hour occurred. Hence neither possibilities 3 and 4 are sufficient in themselves to explain the lack of BSEs during waking in C57BL/6 mice. However, simultaneous administration of 10 mg/kg propranolol and 20 mg/kg pentylenetetrazol provoked numerous BSEs in C57BL/6 mice. This suggests that perhaps C57BL/6 mice, as compared to DBA/2 mice, possess both a more powerful noradrenergic mechanism to suppress spindles and a more weakly functioning mechanism to activate BSEs. Hence possibilities 3 and 4 may both be correct.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of cortical spindles in DBA/2 and C57BL/6 inbred mice

Continuous twenty-four hour EEG recordings were conducted on freely-moving DBA/2 and C57BL/6 inbred mice. No brief spindle episodes (BSEs: 6-7 cps, 1-5 sec duration, high amplitude spindle bursts) were seen in the waking EEG of C57BL/6 mice. BSEs were a conspicuous element of the EEG during active waking (AW) and quiet waking (QW) in DBA/2 mice. BSEs occurred at a 10X faster rate in QW than in AW and had a longer duration. Sleep spindle bursts resembling BSEs were seen in both C57BL/6 and DBA/2 mice, and occasionally were observed to follow a K-complex. Rostropontine, but not midpontine, brainstem transection released spindles in both strains. Pentobarbital produced spindles in both strains. The waveforms of the waves comprising BSEs, sleep spindles, transection-induced spindles and barbiturate spindles were quite similar, though differing in frequencies and amplitude. Genetic factors may be critical for the lack of BSEs during AW and QW in C57BL/6 mice and for the occurrence of BSEs during AW in DBA/2 mice. In contrast, most other rodents whow a third pattern: BSEs only during QW. Since C57BL/6 mice can generate spindles under some circumstances, the absence of spindles during waking reflects some alteration in the mechanisms that control the initiation of BSEs rather than a lack of the circuits required to generate a BSE. These mechanisms are distinct from those processes of arousal that produce the background EEG desynchronization of waking. Following both rostropontine and midpontine transection, the background EEG is desynchronized, yet after rostropontine, but not midpontine transection, BSEs occur freely, at a rate over 200 per hour.

Periodic appearance of theta rhythm in the frontal midline area during performance of a mental task

The distinct theta rhythm in the frontal midline area during performance of a mental task has been called Fm theta. In the present study, periodicity in the appearance of Fm theta was investigated. Thirty male university students were requested to perform the Uchida-Kraepelin test (a test of continuous arithmetic addition) for 5 min continuously after a 2 min practice and 5 min rest. EEGs were recorded monopolarly from disc electrodes placed on Fz and Cz during the whole procedure. A 5 min distribution diagram of appearance of Fm theta was defined according to our criteria. Fm theta appeared in 19 out of 30 subjects. The total appearance time of Fm theta in each subject showed no correlation either to the amount of performed task or to the number of errors. In the subjects who showed a relatively small amount of Fm theta, it tended to appear mainly at 6 points in the 5 min distribution diagram: about 20, 60, 100, 200, 240 and 290 sec after the beginning of calculation. In contrast, Fm theta was almost uniformly distributed in those who showed a larger amount of Fm theta. These results suggest that appearance of Fm theta shows individual differences and there might exist some periodicity of an attention mechanism in certain subjects.

EEG theta waves and psychological phenomena: a review and analysis

In this paper, studies which have explored the relation between EEG theta waves and psychological phenomena in normal human subjects are reviewed. It is noted that increases in theta activity occur in conjunction with several kinds of psychological processes. The importance of ocnsidering properties of theta activity, such as amplitude, rhythmicity and scalp topography when analyzing the relation between theta and psychological processes is emphasized. Although there is some evidence for a relationship between theta and psychological processes, it is concluded that the degree to which properties of theta activity are systematically related to specific psychological processes is not yet known.