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PubMed1996

Magnetic resonance imaging studies of functional brain activation: analysis and interpretation.

We have demonstrated that a time series of echoplanar images can contain low frequency noise components which confound analysis of functional MRI data. In simulated tasks of long duration, the false positive rate from t-test analyses greatly exceeded the statistical probability level. As task durations were shortened, the false positive rate declined. We also demonstrated that voxels representing extensive regions of the brain covary significantly over time. This covariation challenges the independence assumption of t-test and other analytical procedures and likely contributes to the false positive rate. The frequency spectra of many voxels showed relatively little power at higher frequencies with the important exception of some blood vessels (Fig. 12). Experimental designs in which stimulus or task conditions were alternated at these higher frequencies (e.g. 0.083 Hz corresponding to a 6 sec task duration and a 12 sec period for a complete two task cycle) did not show an inflated false positive rate when analyzed by t-test. We used the alternating tasks design with task durations of 8.73 sec, 6.4 sec, and 6.0 sec coupled with a frequency domain analysis strategy in a series of somatosensory, motor, perceptual, and working memory experiments. This combination of design and analysis was successful in identifying reliable activations across groups of subjects with a minimum of apparently spurious activations. By introducing a 180 degrees phase shift by reversing task order, we have been able to eliminate the contribution of most high frequency noise sources (such as large blood vessels). By segregating low frequency noise from the frequency of stimulus alternation, we routinely generate stable results in the presence of low frequency noise and drift. Despite the usefulness of the rapid task alternation and frequency domain techniques demonstrated here, there are potential problems and limitations in their application: 1. The short duration of our tasks results in an approximately sinusoidal activation waveform. With longer duration tasks, the activation time course would appear more square with a more complex frequency spectrum than the single peak demonstrated above. In such circumstances we have used convolution analysis with an expected waveform (McCarthy et al. 1996), similar to the approach of Bandettini et al. (1993). 2. If the activation in one task condition is significantly delayed and extends well into the period of the second task, it will be difficult to determine which task produced the activation. This problem is not specific to frequency analysis, and would occur as well for t-tests. One solution we have used is running a single active task against a relatively neutral control such as fixation to determine the usual activation dynamics of the active task. 3. Common activations by two alternating tasks are de-emphasized. This problem is also not specific to frequency analysis, and in most circumstances is an advantage rather than a disadvantage. However, if uncertain as to whether a task is capable of producing any activation, we have again used the strategy of running the task against a relatively neutral control. 4. Some tasks do not lend themselves to the short durations used here. 5. The frequency domain procedures used are conservative and may underestimate the true anatomical extent of the activation. In practice we compute t-tests in addition to the frequency domain techniques to guard against this possibility. Many of the advantages of the procedures described here are due to the alternation of short duration tasks rather than the application of frequency domain techniques per se. However, the success of these techniques in isolating periodic task-related signal changes suggest that a more complex design with concurrent stimulation presented at different frequencies might be feasible. Such designs may have advantages in that categories of stimuli would not be presented in isolation but against a changing ba

Artifacts↗
PubMed1978

A brain function monitor for use during anaesthesia. Preliminary report.

This simple on-line monitor provides simultaneous noninvasive quantification of continuous processes within the brain, by measuring the augmented delta quotient (ADQ; the proportion of low frequency components in the electroencephalogram). The response of the ADQ, both during experiments in animals and in children undergoing surgery, during cardiopulmonary bypass with and without hypothermia, demonstrates that this concept may prove valuable both to monitor anaesthetic depth and to warn of impending cerebral impairment.

Anesthesia, General↗
PubMed1999

Assessment and calibration of a low-frequency system for electrical impedance tomography (EIT), optimized for use in imaging brain function in ambulant human subjects.

An EIT system has been produced that has been optimized for imaging impedance changes with scalp electrodes during brain activity in ambulant subjects. It can record from 225 Hz to 65 kHz, has a small headbox on a lead 10 m long, and has software programmable electrode selection. In calibration experiments in a small cylindrical tank filled with potassium chloride solution and samples of cucumber, noise was less than 1% with averaging, and acceptable images were produced at frequencies down to 1800 Hz. This suggests that EIT can be performed at low frequencies, which are likely to give larger signals during brain activity. Future work will include trials in humans and improvement of the current source and isolation.

Brain Chemistry↗
PubMed1984

Testing a theory of brain function by computer methods. III. Detecting cerebral asymmetry in normal adults.

Pursuing a plan for overall testing of the timing and sequencing of brain processes, testing techniques are introduced for probing a normal adult's short-term central processes, especially those which are employed in reading a digit span of 6 numbers or less. The tests are administered by means of a personal computer and can provide information on the individual subject's characteristic sequencing and timing of particular central processes. In a subject whose first language is read from left to right, the presented tests reported in this paper reveal an asymmetry in normal adults wherein digits presented in the left visual field are processed more efficiently than those presented in the right visual field. It is suggested that the right hemisphere 'holds the image' while the left hemisphere 'transforms' the spatial image into a temporal sequence for use in speech. The 'right-positioned' or 'later' components must be held at least until a successful spoken response is completed.

Brain↗
PubMed1986

[Brain function and level of consciousness in fentanyl anesthesia in heart surgery].

The level of consciousness and the supply/demand ratio of oxygen in the brain was studied in anaesthetized patients undergoing open heart surgery. Anaesthesia was accomplished with intravenous fentanyl; 26 patients received 25 micrograms/kg and 24 patients received 50 micrograms/kg fentanyl. In addition only pancuronium bromide was administered for muscular relaxation; all patients were ventilated with 100% oxygen. The following measurements were made during induction and prior to cardiopulmonary bypass and in the first ten minutes of bypass: 1. EEG with the Klein EEG Analyzer. This instrument permits simultaneous analysis of frequency and amplitude while eliminating muscular artifacts. 2. Cerebral oxygen with the Niroscope. This instrument uses an infrared light beam through the brain to evaluate cerebral oxygen sufficiency. 3. Oxygen supply/demand ratio in the whole body, estimated from mixed venous oxygen saturation measured with a fiberoptic pulmonary artery catheter. Clinical unconsciousness occurred in all patients within about 30 s after the administration of fentanyl. Simultaneously the EEG showed a significant decrease in frequency and an increase in amplitude. With the Niroscope no change in oxygen supply and demand was seen in any patients. This is in contrast to previous studies with thiopental, where changes were seen. A slight increase in mixed venous oxygen saturation was observed. This indicates an increase in the total oxygen supply/demand ratio, probably due to decreased muscle metabolism induced by pancuronium bromide paralysis. From the end of induction until cardiopulmonary bypass a slight increase in cerebral electrical activity was observed; an additional increase occurred in the first ten minutes of bypass.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗
PubMed1995

An ROC approach for evaluating functional brain MR imaging and postprocessing protocols.

A method that can be used to evaluate the performance of MRI methods for detecting discrete regional activations using functional MRI is presented. Computer derived receiver-operator-characteristic (ROC) curves have been used to evaluate quantitatively a range of conditions encountered in functional MRI studies. ROC analysis allows multiple acquisition strategies and multiple postprocessing strategies to be quantitatively and objectively compared. The authors first present this analysis technique and then illustrate its use for assessing the relative performances of different functional MRI data acquisition strategies using different gradient echo, echoplanar imaging protocols. In addition, the authors have used the ROC analysis to evaluate and compare several methods for analyzing functional MRI data to extract regions of activation. This approach to assessing the performance of different methods is of general use and can be applied to evaluate other data acquisition protocols and postprocessing methods.

Algorithms↗
PubMedDate not supplied

[The effect of antioxidants on functional brain disorders caused by low-intensity ionizing radiation].

The effects of daily intraperitoneal injections of alpha-tocopherol (30 mg/kg per day) and synthetic antioxidant IHFAN-30 (30 mg/day) in rats were compared during low-level ionizing radiation (10 days, dose rate 5 mGy/h, total dose 1.2 Gy). There were analysed: (1) amplitude of population spike of hippocampal slices; (2) endogenous phosphorylation in vitro of hippocampal synaptic proteins in the presence of cAMP; (3) formation, manifestation and reduction of food-procuring reflex. The findings showed that antioxidants made some correction of the functional state of hippocampal slices and cAMP-dependent phosphorylation system activity in brain cells from irradiated animals. No influence on training and memory functions was detected.

Animals↗
PubMed2006

Executive brain functions after exposure to nocturnal traffic noise: effects of task difficulty and sleep quality.

The after-effects of nocturnal traffic noise on cognitive performance and inhibitory brain activity were investigated. Twenty participants (18-30 years) performed an easy and a difficult visual Go/Nogo task with simultaneous EEG recording after a quiet night and then during three nights when aircraft noise was presented with equivalent noise levels of 39, 44, and 50 dBA, respectively, between 11 p.m. to 7 a.m. Based on subjective sleep quality rating, participants were separated into "good" versus "bad" sleepers. The performance and inhibition-related components (N2, P3) of event-related potentials were analysed. The N2 and P3 amplitudes were smaller and latencies were prolonged in the difficult than in the easy task. This effect was more pronounced for Nogo than for Go trials. The Nogo-P3 amplitude was smaller in Noise than in "Quiet" conditions in the difficult task only. In the difficult task, the Nogo-P3 latency was prolonged in bad sleepers than in good sleepers. The Nogo-P3 amplitude was reduced in Noise as compared to "Quiet" conditions in bad sleepers only. Sleep quality in bad sleepers worsened steadily with increasing noise levels. No effects of noise or subjective sleep quality on performance were found. Inhibitory processes appear to be selectively impaired after nocturnal noise exposure. The task difficulty and perceived sleep quality are important factors modulating noise effects. The results suggest that nocturnal traffic noise increase physiological costs for inhibitory functioning on the day even if no overt performance decrement is observed.

Action Potentials↗
PubMed1994

The inositol trisphosphate receptor gene family: implications for normal and abnormal brain function.

1. The phosphatidyl inositol (PI) second messenger system has been extensively investigated in the past decade. This complex pathway results in the production of two second messengers, one of which, inositol 1,4,5-trisphosphate, will be the focus of this review. 2. The intracellular receptor for this second messenger (IP3R) has been purified, reconstituted and extensively characterized in both brain and peripheral tissues. 3. Localization and functional studies show that IP3 binding causes the receptor to release portions of the intracellular calcium stores. 4. Multiple modulators of the receptor have been identified, including pH, calcium concentration, adenine nucleotide concentration and phosphorylation. 5. The cDNA for this molecule has been cloned from a number of sources. Studies of the molecular structure of the receptor have revealed additional levels of complexity including multiple alternative splicing events in the initially cloned cerebellar (Type I) receptor, as well as the existence of highly related but distinct cDNAs which likely reflect a gene family. 6. There is suggestive evidence linking the PI system, and thus the IP3R, to bipolar disorder and the actions of lithium.

Animals↗
PubMed1995

Applications of magnetic resonance imaging to the study of human brain function.

Important questions relating to the coupling of local neuronal activity to the hemodynamic response measured using functional magnetic resonance imaging (fMRI), as well as issues concerning imaging sequence, paradigm design and data analysis processing, have been addressed during the past year. Initial fMRI studies identified visual, somatosensory, auditory and motor activation areas in the primary cortices. Current 'second generation' studies aim to identify changes in the fMRI signal associated with specific tasks and stimulus parameters. Dynamic aspects of brain processing for performing higher order cognitive functions, such as language, attention, mental imagery, and learning and memory, have also been explored.

Animals↗
PubMed1992

Time course EPI of human brain function during task activation.

Using gradient-echo echo-planar MRI, a local signal increase of 4.3 +/- 0.3% is observed in the human brain during task activation, suggesting a local decrease in blood deoxyhemoglobin concentration and an increase in blood oxygenation. Images highlighting areas of signal enhancement temporally correlated to the task are created.

Brain↗
PubMed1993

Evaluation of brain function in acute carbon monoxide poisoning with multimodality evoked potentials.

The median nerve somatosensory evoked potentials (SEP), pattern reversal visual evoked potentials (VEP), and brain stem auditory evoked potentials (BAEP) were studied in 109 healthy adults and in 88 patients with acute carbon monoxide (CO) poisoning. The upper limits for normal values of peak and interpeak latencies of multimodalities of evoked potentials in the reference group were established by a stepwise multiple regression analysis. SEP changes selectively affecting N32 and N60 were found in 78.8% of patients. There was prolonged P100 latency of VEP in 58.2% of the cases examined. The prevalence of BAEP abnormalities in comatose patients (36%) was significantly higher than that (8.6%) in conscious patients. BAEP abnormalities were most frequently seen in comatose patients who had diminished brain stem reflexes (77.8%). It has been found that a consistent abnormality involving N20 and subsequent peaks in SEP, a remarkable prolongation of P100 latency in VEP, or a prolongation of III-V interpeak latency in BAEP as well as the reoccurrence of evoked potential abnormalities after initial recovery all indicate unfavorable outcomes in patients with acute CO poisoning. The multimodality evoked potentials have proved to be sensitive indicators in the evaluation of brain dysfunction and in the prediction of prognosis of acute CO poisoning and the development of delayed encephalopathy.

Adult↗