ABSTRACT
EEG/VEP and fMRI responses to periodic visual stimulation are reported. The purpose of these experiments was to look for similar patterns in the time series produced by each method to help understand the relationship between the two. The stimulation protocol was the same for both sets of experiments and consisted of five complete cycles of checkerboard pattern reversal at 1.87 Hz for 30 s followed by 30 s of a stationary checkerboard. The fMRI data was analyzed using standard methods, while the EEG was analyzed with a new measurement of activation-the VEPEG. Both VEPEG and fMRI time series contain the fundamental frequency of the stimulus and quasi harmonic components-an unexplained double frequency commonly found in fMRI data. These results have prompted a reappraisal of the methods for analyzing fMRI data and have suggested a connection between our findings and much older published invasive electrophysiological measurements of blood flow and the partial pressures of oxygen and carbon dioxide. Overall our new analysis suggests that fMRI signals are strongly dependant on hydraulic blood flow effects. We distinguish three categories of fMRI signal corresponding to: focal activated regions of brain tissue; diffuse nonspecific regions of steal; and major cerebral vessels of arterial supply or venous drainage. Each category of signal has its own finger print in frequency, amplitude, and phase. Finally, we put forward the hypothesis that modulations in blood flow are not only the consequence but are also the cause of modulations in functional activity.
Subject(s)
Arousal/physiology , Electroencephalography , Evoked Potentials, Visual/physiology , Magnetic Resonance Imaging , Visual Perception/physiology , Adolescent , Adult , Brain Mapping , Child , Color Perception/physiology , Humans , Image Processing, Computer-Assisted , Male , Middle Aged , Motion Perception/physiology , Occipital Lobe/blood supply , Occipital Lobe/physiology , Pattern Recognition, Visual/physiology , Photic StimulationABSTRACT
OBJECTIVES: To analyse the epidemiology of Tuberculosis and determine the characteristics of patients infected by HIV vs those not infected. DESIGN: A descriptive-retrospective study. SETTING: Ibiza and Formentera Health Area. PATIENTS: 268 patients over 16 diagnosed with TB between 7/1/1987 and 12/31/1993. MEASUREMENTS AND MAIN RESULTS: The highest accumulated annual incidence was detected in 1989 (82.4/100,000 inhabitants), but had decreased considerably by 1993 (42.8/100,000). The proportion of HIV+ cases increased to 37.0% of the total in 1993. 75% of the total were male and 57.5% between 20 and 39 (x = 38.1; SD = 15.4). 63.1% had pulmonary TB, 60.8% producing bacilli, 19.8% were HIV+, of which 47.2% were intravenous drug users and 20.8% homosexuals. There was a 75.4% cure rate, 4.9% who left treatment and 16.1% lost during follow-up. CONCLUSIONS: During the study period a progressive increase in the proportion of cases with HIV infection was observed. Control and follow-up of Tuberculosis was more difficult in these patients.
