Jackson Beatty

Magnetic localization of a dipolar current source implanted in a sphere and a human cranium

Magnetic fields produced by a dipolar source implanted in a spherical conductor and a human cranial specimen were measured in the magnetoencephalogram (MEG). The location of the source was accurately computed in the spherical conductor from the identified magnetic field extrema using equations for a current dipole in a sphere. This same method was insufficient for localizing the source in a human cranium, where magnetic field maps appeared as distortions from the classical dipolar pattern. A more complete computer modeling procedure was used, adjusting for the non-spherical dimensions of the recording matrix on the cranium. By fitting the gradient of computer simulated fields to those measured outside the cranium, the accuracy of source localization was substantially improved. The greatest distortion of the extracranial magnetic field was an inequality in the measured amplitude of the two extrema, produced by an increased distance and angle of the MEG probe when recording over the lower face and ear. However, gross heterogeneities in the resistance of the skull due to a craniectomy and an implanted insulating balloon had a negligible effect on the extracranial magnetic field pattern.

Detection and recognition: Concurrent processes in perception

In two experiments, event-related brain potentials (ERPs) were recorded while subjects performed a simultaneous detection and recognition task. Ten subjects listened to pure tones in noise and reported both whether a target tone had occurred (using a four-category confidence rating scale) and whether the target was one of two (Experiment 1) or four (Experiment 2) tones differing in frequency. The amplitudes of three ERP components were found to be differentially related to detection and recognition performance. The early N100 component varied with processing related only to detection, while the late P300 varied with both detection and recognition, and a later slow positive shift varied only with recognition and not with detection. While the latenciee of both N100 and P300 increased for less confident target detections, there were no differences in the latencies of these ERP components between correctly and incorrectly identiffed targets. Recognition performance was above the level expected by chance even when subjects reported that no target had been presented. The results indicate that brain potential components can be used to disclose temporal features of the processing of a stimulus by the nervous system and support the view that detection and recognition are partially independent, concurrent processes in perception.

Towards effective and rewarding data sharing.

Recently issued NIH policy statement and implementation guidelines (National Institutes of Health, 2003) promote the sharing of research data. While urging that “all data should be considered for data sharing” and “data should be made as widely and freely available as possible” the current policy requires only high-direct-cost (>US

Similar effects of feedback signals and instructional information on EEG activity

500,000/yr) grantees to share research data, starting 1 October 2003. Data sharing is central to science, and we agree that data should be made available.

Prolongation of magnetic resonance T2 time in hippocampus of human patients marks the presence and severity of Alzheimer's disease

Abstract Normal human subjects may systematically modify the proportions of alpha and beta frequency activity in the occipital EEG in either of two conditions. They may be provided with information giving appropriate strategies for producing such changes or with only second by second feedback about their success in achieving the response criteria. Subjects provided with both did no better than subjects given prior information or feedback alone. Subjects who received no treatment, or who were given information inappropriately matched to the feedback signal, showed no systematic changes. The similarity in both the development and final magnitude of the differential responsiveness in the groups which learned emphasizes the difficulty in ascribing learned changes to the effects of feedback if subjects are also informed about the nature of the task.

Effects of initial alpha wave abundance and operant training procedures on occipital alpha and beta wave activity

Spin-spin relaxation time (T2) was measured in the hippocampal formation, thalamus, and cortical white matter in 13 patients with probable Alzheimers disease (AD), 11 elderly normal individuals, 23 healthy young persons, and 9 subjects diagnosed with multi-infarct dementia. A 0.04 tesla magnetic resonance scanner was used. Hippocampal T2 values for all AD patients exceeded those of any non-AD individual, regardless of age or dementia due to infarction. Further, these T2 values were highly correlated (+ 0.96) with the severity of functional and cognitive impairment of the AD patients. This T2 prolongation was not observed at the other sites examined. These results suggest that hippocampal T2 prolongation may provide a specific marker by which AD pathology can be detected, characterized, and followed in vivo.

Intracellular currents of interictal penicillin spikes: Evidence from neuromagnetic mapping

Operant methods were used to increase differentially the abundance of occipital EEG waves in the alpha (8-12 Hz) and beta (above 13 Hz) frequency bands of naive undergraduate Ss in the presence of a discriminative stimulus. Ss were grouped by the amount of alpha wave activity in their pretraining EEG. Operant training with continuous reinforcement produced reliable and orderly changes in EEG spectra as a function of reinforcement contingency. Baseline alpha abundance predicted only the mean level of alpha output over trials, not the efficiency of training. Matched yoked controls showed no difference in EEG spectra between the two reinforcement conditions.

Slow potential shifts of human brain during forewarned reaction

To analyze the net intracellular current produced by interictal spikes, we mapped the extracranial magnetic fields of the rat brain following application of penicillin to the right or left medial cingulate cortex. Averaged interictal spikes in both the magnetoencephalogram (MEG) and in the electrocorticogram (ECoG) were composed of 4 temporal components, a biphasic spike and slow wave. Magnetic field maps for each of these components indicated a source at the location of penicillin application, with intracellular currents oriented perpendicular to the surface of the cingulate cortex, along the axis of the major pyramidal cells. The polarity of the magnetic fields for each of the components was reversed between the two cingulate groups, reflecting the respective orientation of pyramidal cells between the juxtaposed faces of the medial cingulate cortex. This neuromagnetic study of net intracellular current complements and extends the analysis of extracellular currents within the penicillin focus obtained using laminar electrodes. These data also demonstrate how animal neuromagnetometry may provide an empirical foundation for the neurogenesis of the MEG and a new unique method for the non-invasive study of population cell physiology.

Catecholamine correlates of radar monitoring performance.

The slow brain potentials observed during the 4 sec interstimulus interval (ISI) of a CNV paradigm were investigated by a factorial manipulation of the parameters that have been identified as affecting the CNV at ISIs of 1 or 2 sec. Subjects performed choice and simple reaction time (RT) tasks under all possible combinations of auditory and visual warning (S1) and imperative (S2) stimuli. The choice task involved easy or difficult intensity discriminations at S2, which were forewarned by S1s that cued the subject as to the level of difficulty for that trial. Principal components analysis (PCA) of the data revealed two negative afterwave factors and a late positive component (LPC) related to warning stimulus variables, and a late negative shift preceding S2 that was related to motor preparation. The negative afterwave components were enhanced in the choice RT task, and the earlier of the two components showed a modality-specific distribution. The LPC factor was also enhanced in the choice task and was further enhanced by S1s signaling difficult discriminations. Additionally, the LPC was larger for visual S1s. The S1-related components are interpreted in terms of orienting, while the later shift is identified with the readiness potential and motor preparation. The results support the notion that the conventionally recorded CNV consists of S1 evoked and response-related potentials rather than non-specific and modality-specific anticipatory potentials.

Genomic regulation of natural variation in cortical and noncortical brain volume.

Two experiments were concluded in which target detection performance was measured for male and female subjects engaged in a simulated radar monitoring task. In the first, 20 subjects performed for 2 h; in the second, 28 subjects for 1 h. Adrenaline excretion rate was significantly correlated with performance efficiency in both cases. Task duration and subject sex had no effect upon that correlation. The results of the two experiments were combined to show a general adrenaline/performance relationship.