Thomas Prieto

Human Brain Language Areas Identified by Functional Magnetic Resonance Imaging

Functional magnetic resonance imaging (FMRI) was used to identify candidate language processing areas in the intact human brain. Language was defined broadly to include both phonological and lexical–semantic functions and to exclude sensory, motor, and general executive functions. The language activation task required phonetic and semantic analysis of aurally presented words and was compared with a control task involving perceptual analysis of nonlinguistic sounds. Functional maps of the entire brain were obtained from 30 right-handed subjects. These maps were averaged in standard stereotaxic space to produce a robust “average activation map” that proved reliable in a split-half analysis. As predicted from classical models of language organization based on lesion data, cortical activation associated with language processing was strongly lateralized to the left cerebral hemisphere and involved a network of regions in the frontal, temporal, and parietal lobes. Less consistent with classical models were (1) the existence of left hemisphere temporoparietal language areas outside the traditional “Wernicke area,” namely, in the middle temporal, inferior temporal, fusiform, and angular gyri; (2) extensive left prefrontal language areas outside the classical “Broca area”; and (3) clear participation of these left frontal areas in a task emphasizing “receptive” language functions. Although partly in conflict with the classical model of language localization, these findings are generally compatible with reported lesion data and provide additional support for ongoing efforts to refine and extend the classical model.

Measures of postural steadiness: differences between healthy young and elderly adults

Measures of postural steadiness are used to characterize the dynamics of the postural control system associated with maintaining balance during quiet standing. The objective of this study was to evaluate the relative sensitivity of center-of-pressure (COP)-based measures to changes in postural steadiness related to age. A variety of time and frequency domain measures of postural steadiness were compared between a group of twenty healthy young adults (21-35 years) and a group of twenty healthy elderly adults (66-70 years) under both eyes-open and eyes-closed conditions. The measures that identified differences between the eyes-open and eyes-closed conditions in the young adult group were different than those that identified differences between the eye conditions in the elderly adult group. Mean velocity of the COP was the only measure that identified age-related changes in both eye conditions, and differences between eye conditions in both age groups. The results of this study will be useful to researchers and clinicians using COP-based measures to evaluate postural steadiness.

Neural Basis of Endogenous and Exogenous Spatial Orienting: A Functional MRI Study

Whole-brain functional magnetic resonance imaging (MRI) was used to examine the neural substrates of internally (endogenous) and externally (exogenous) induced covert shifts of attention. Thirteen normal subjects performed three orienting conditions: endogenous (location of peripheral target predicted by a central arrow 80 of the time), exogenous (peripheral target preceded by a noninformative peripheral cue), and control (peripheral target preceded by noninformative central cue). Behavioral results indicated faster reaction times (RTs) for valid than for invalid trials for the endogenous condition but slower RTs for valid than for invalid trials for the exogenous condition (inhibition of return). The spatial extent and intensity of activation was greatest for the endogenous condition, consistent with the hypothesis that endogenous orienting is more effortful (less automatic) than exogenous orienting. Overall, we did not observe distinctly separable neural systems associated with the endogenous and exogenous orienting conditions. Both exogenous and endogenous orienting, but not the control condition, activated bilateral parietal and dorsal premotor regions, including the frontal eye fields. These results suggest a specific role for these regions in preparatory responding to peripheral stimuli. The right dorsolateral prefrontal cortex (BA 46) was activated selectively by the endogenous condition. This finding suggests that voluntary, but not reflexive, shifts of attention engage working memory systems.

Simultaneous ERP and fMRI of the auditory cortex in a passive oddball paradigm.

Infrequent occurrences of a deviant sound within a sequence of repetitive standard sounds elicit the automatic mismatch negativity (MMN) event-related potential (ERP). The main MMN generators are located in the superior temporal cortex, but their number, precise location, and temporal sequence of activation remain unclear. In this study, ERP and functional magnetic resonance imaging (fMRI) data were obtained simultaneously during a passive frequency oddball paradigm. There were three conditions, a STANDARD, a SMALL deviant, and a LARGE deviant. A clustered image acquisition technique was applied to prevent contamination of the fMRI data by the acoustic noise of the scanner and to limit contamination of the electroencephalogram (EEG) by the gradient-switching artifact. The ERP data were used to identify areas in which the blood oxygenation (BOLD) signal varied with the magnitude of the negativity in each condition. A significant ERP MMN was obtained, with larger peaks to LARGE deviants and with frontocentral scalp distribution, consistent with the MMN reported outside the magnetic field. This result validates the experimental procedures for simultaneous ERP/fMRI of the auditory cortex. Main foci of increased BOLD signal were observed in the right superior temporal gyrus [STG; Brodmann area (BA) 22] and right superior temporal plane (STP; BA 41 and 42). The imaging results provide new information supporting the idea that generators in the right lateral aspect of the STG are implicated in processes of frequency deviant detection, in addition to generators in the right and left STP.

Characterization and modeling of postural steadiness in the elderly: a review

The methods that have been used to evaluate the static (postural steadiness) and dynamic (postural stability) performance of the postural control system are discussed. Time and frequency domain measures of postural steadiness are described. Research of age-related changes in the postural control system, with an emphasis on postural steadiness evaluations, is summarized. Control systems and biomechanical models of the postural control system are considered. The evaluation of bilateral asymmetries in postural sway and weight distribution, with a dual force plate balance platform, is briefly discussed. >

Measurement and correction of microscopic head motion during magnetic resonance imaging of the brain.

Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.

Autonomic dysfunction, vasomotor rhinitis, and extraesophageal manifestations of gastroesophageal reflux

OBJECTIVE: Several recent reports suggest there may be a relationship between chronic rhinitis and extraesophageal manifestations of gastroe-sophageal reflux (EER). It is hypothesized that this relationship is a result of autonomic nervous system (ANS) dysfunction. STUDY DESIGN: Patients with isolated vasomotor rhinitis (VR), both VR and EER, and a control group were studied by a battery of tests designed to objectively evaluate ANS function. In addition all 3 groups underwent barium esophagogram and 4-site (proximal pharynx, distal pharynx, proximal esophagus, and distal esophagus) ambulatory pH monitoring. Adult patients fulfilling diagnostic criteria for VR, and with both VR and EER underwent objective ANS testing in a recently developed ANS testing laboratory. The control group consisted of age- and sex-matched adults without diagnostic criteria for VR or EER. RESULTS: In patients with VR only (n = 9), 2 patients had a positive esophagogram, whereas a positive pharyngeal reflux probe was found in 1 and an abnormal composite autonomic scoring scale (CASS) was found in 8 (mean VR CASS = 1.750 vs control CASS 0.556, P = .02). The group with VR and EER (n = 12) had a positive esophagogram in 10 patients, positive pharyngeal reflux by probe in 9, and all 12 had an abnormal CASS (mean CASS VR/EER = 2.909 vs CASS control = 0.556, P = .001 and vs VR CASS = 1.750, P = .05). The control patients (n = 9) had normal transesopohageal gastroduo-denoscopy in 8, 1 had a positive pharyngeal probe study, and all 9 had a normal CASS. In addition ANS testing in patients with diagnostic criteria for both VR/EER revealed statistically significant evidence of an adrenergic deficit as compared with control patients on the basis of mean phase II blood pressure response to Valsalva maneuver (mean phase II VR/EER = −16.730 vs control = −7.780, P = .05). In the VR only group, the phase II blood pressure decrease was greater than in control patients, but did not reach statistical significance (mean phase II VR = −9.370 vs control = − 7.780, P = 0.672). CONCLUSION: Patients with VR and VR/EER have objective evidence of ANS dysfunction when compared with a group of age- and sex-matched control patients. Patients with both VR/EER demonstrate a significantly greater degree of ANS dysfunction than patients with isolated VR. The mechanism by which VR and EER interact is not entirely clear, but ANS dysfunction is objectively associated with both disorders. In addition, patients with VR/EER seem to demonstrate hypo-function of the adrenergic component of the ANS, in contrast to the generally held hypothesis that VR results from increased cholinergic activity. Further characterization of the type of ANS abnormality may allow the development of novel pharmacologic therapies for these disorders.

Ballistocardiogram artifact reduction in the simultaneous acquisition of auditory ERPS and fMRI

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are now being combined to analyze brain function. Confounding the EEG signal acquired in the MR environment is a ballistocardiogram artifact (BA), which is predominantly caused by cardiac-related body movement. The objective of this study was to develop and evaluate a method for reducing these MR-induced artifacts to retrieve small auditory event-related potentials (ERPs) from EEG recorded during fMRI. An algorithm for BA reduction was developed that relies on timing information obtained from simultaneous electrocardiogram (ECG) recordings and subsequent creation of an adaptive BA template. The BA template is formed by median-filtering 10 consecutive BA events in the EEG signal. The continuously updated template is then subtracted from each BA in the EEG. The auditory ERPs are obtained through signal averaging of the remaining EEG signal. Experimental and simulated ERP data were estimated to assess effectiveness of the BA reduction. Simulation showed that the algorithm reduced BA without significantly altering the morphology of a signal periodically inserted in the EEG. Auditory ERP data, obtained in a 1.5-T scanner during a passive auditory oddball paradigm and processed with the BA reduction algorithm, were comparable to data recorded in a mock scanner outside the magnetic field with the same experimental paradigm. It is concluded that through adequate reduction of the BA, relatively small auditory ERPs can be acquired in the MR environment.

Autonomic Nervous System Evaluation of Patients With Vasomotor Rhinitis

Objective To demonstrate the utility of quantitative neurological laboratory testing of autonomic nervous system dysfunction and to apply this methodology to further study the relation of chronic vasomotor (nonallergic) rhinitis to the autonomic nervous system.

Evaluation of the autonomic nervous system

This article has reviewed the laboratory evaluation of autonomic disorders. Autonomic testing can be divided into the assessment of three functional domains: sudomotor (assessed best by the thermoregulatory sweat test or QSART), cardiovagal (assessed by the Valsalva ratio and heart rate response to deep breathing or standing up), and adrenergic (assessed by the blood pressure response to the Valsalva maneuver or head-upright tilt). Tables 2 and 3 summarize the test findings in a variety of clinical disorders affecting autonomic nervous system function.