Gamma coherence and conscious perception.

BACKGROUND: High-frequency (e.g., gamma 30 to 50 Hz) coherent neural activity has been postulated to underlie binding of independent neural assemblies and thus integrate processing across distributed neuronal networks to achieve a unified conscious experience. Prior studies suggest that gamma activity may play a role in perceptual mechanisms, but design limitations raise concerns. Thus, controversy exists as to the hypothesis that gamma activity is necessary for perceptual awareness. In addition, controversy exists as to whether the primary sensory cortices are involved directly in the mechanisms of conscious perception or just in processes prior to conscious awareness. OBJECTIVE: To investigate the relation of gamma coherence and perception. METHODS: Digital intracranial electrocorticographic recordings from implanted electrodes were obtained in six patients with intractable epilepsy during a simple somatosensory detection task for near-threshold stimuli applied to the contralateral hand. Signal analyses were then conducted using a quantitative approach that employed two-way Hanning digital bandpass filters to compute running correlations across pairs of channels at various time epochs for each patient and each perception state across multiple bandwidths. RESULTS: Gamma coherence occurs in the primary somatosensory cortex approximately 150 to 300 milliseconds after contralateral hand stimuli that are perceived, but not for nonperceived stimuli, which did not differ in character/intensity or early somatosensory evoked potentials. CONCLUSION: The results are consistent with the possible direct involvement of primary sensory cortex in elemental awareness and with a role for gamma coherence in conscious perception.

Design of a microprocessor-based sphygmomanometer.

This paper describes the implementation on a microprocessor of a new method for the indirect measurement and recording of the systolic and diastolic blood pressure in humans. The technique is based on a statistical analysis of the cardiac pulse pressure signal. Polynomial relations are derived between the amplitude of the pulsatile pressure waveforms at the systolic and diastolic points and the amplitude of pulse signals detected when the artery is fully occluded. With the dual objective of automating the measurement procedure and minimizing errors, an electronic analog-digital sphygmomanometer that contains suitable electronic instrumentation was developed. The functions of processing the pressure signal, automating the measurement, and recording the results are performed and controlled by a microprocessor. A laboratory prototype embodying this approach was constructed and its performance and reliability were verified using a series of clinical tests. The test results indicate that the device is accurate within acceptable bounds for automated blood pressure instruments.

Development of a microprocessor-based adaptive technique for blood pressure measurements.

The paper introduces a new microprocessor-based adaptive technique for the indirect measurement of the systolic and diastolic pressure in humans. The technique is based upon a statistically consistent relationship between the amplitude of the pulsative pressure waveform at the systolic and diastolic points and the amplitude of pulse signals detected when the artery is fully occluded. An adaptive measurement philosophy has been implemented in the design of an electronic analog-digital sphygmomanometer which, in addition to a pressure transducer, contains suitable electronic instrumentation for processing and displaying the electronic signals. A dedicated microprocessor is used to store statistical relations and control the operation of the device. Verification of overall system accuracy is accomplished via direct comparison with manual auscultatory measurements. Clinical testing of a prototype indicates satisfactory performance; measurement errors are maintained well within proposed standards for automated sphygmomanometers.