Biomedical subjects

B R Rosen

Publications and source records attributed to B R Rosen.

At least 19 recordsLinked to original sources

PubMed2006

The value of multichannel MEG and EEG in the presurgical evaluation of 70 epilepsy patients.

OBJECTIVE: To evaluate the sensitivity of a simultaneous whole-head 306-channel magnetoencephalography (MEG)/70-electrode EEG recording to detect interictal epileptiform activity (IED) in a prospective, consecutive cohort of patients with medically refractory epilepsy that were considered candidates for epilepsy surgery. METHODS: Seventy patients were prospectively evaluated by simultaneously recorded MEG/EEG. All patients were surgical candidates or were considered for invasive EEG monitoring and had undergone an extensive presurgical evaluation at a tertiary epilepsy center. MEG and EEG raw traces were analysed individually by two independent reviewers. RESULTS: MEG data could not be evaluated due to excessive magnetic artefacts in three patients (4%). In the remaining 67 patients, the overall sensitivity to detect IED was 72% (48/67 patients) for MEG and 61% for EEG (41/67 patients) analysing the raw data. In 13% (9/67 patients), MEG-only IED were recorded, whereas in 3% (2/67 patients) EEG-only IED were recorded. The combined sensitivity was 75% (50/67 patients). CONCLUSION: Three hundred and six-channel MEG has a similarly high sensitivity to record IED as EEG and appears to be complementary. In one-third of the EEG-negative patients, MEG can be expected to record IED, especially in the case of lateral neocortical epilepsy and/or cortical dysplasia.

Adolescent↗

PubMed2006

Top-down facilitation of visual recognition.

Cortical analysis related to visual object recognition is traditionally thought to propagate serially along a bottom-up hierarchy of ventral areas. Recent proposals gradually promote the role of top-down processing in recognition, but how such facilitation is triggered remains a puzzle. We tested a specific model, proposing that low spatial frequencies facilitate visual object recognition by initiating top-down processes projected from orbitofrontal to visual cortex. The present study combined magnetoencephalography, which has superior temporal resolution, functional magnetic resonance imaging, and a behavioral task that yields successful recognition with stimulus repetitions. Object recognition elicited differential activity that developed in the left orbitofrontal cortex 50 ms earlier than it did in recognition-related areas in the temporal cortex. This early orbitofrontal activity was directly modulated by the presence of low spatial frequencies in the image. Taken together, the dynamics we revealed provide strong support for the proposal of how top-down facilitation of object recognition is initiated, and our observations are used to derive predictions for future research.

Cerebral Cortex↗

PubMed2004

Age-related alterations in white matter microstructure measured by diffusion tensor imaging.

Cerebral white matter (WM) undergoes various degenerative changes with normal aging, including decreases in myelin density and alterations in myelin structure. We acquired whole-head, high-resolution diffusion tensor images (DTI) in 38 participants across the adult age span. Maps of fractional anisotropy (FA), a measure of WM microstructure, were calculated for each participant to determine whether particular fiber systems of the brain are preferentially vulnerable to WM degeneration. Regional FA measures were estimated from nine regions of interest in each hemisphere and from the genu and splenium of the corpus callosum (CC). The results showed significant age-related decline in FA in frontal WM, the posterior limb of the internal capsule (PLIC), and the genu of the CC. In contrast, temporal and posterior WM was relatively preserved. These findings suggest that WM alterations are variable throughout the brain and that particular fiber populations within prefrontal region and PLIC are most vulnerable to age-related degeneration.

Adult↗

PubMed2003

Can the cerebral metabolic rate of oxygen be estimated with near-infrared spectroscopy?

We have measured the changes in oxy-haemoglobin and deoxy-haemoglobin in the adult human brain during a brief finger tapping exercise using near-infrared spectroscopy (NIRS). The cerebral metabolic rate of oxygen (CMRO2) can be estimated from these NIRS data provided certain model assumptions. The change in CMRO2 is related to changes in the total haemoglobin concentration, deoxy-haemoglobin concentration and blood flow. As NIRS does not provide a measure of dynamic changes in blood flow during brain activation, we relied on a Windkessel model that relates dynamic blood volume and flow changes, which has been used previously for estimating CMRO2 from functional magnetic resonance imaging (fMRI) data. Because of the partial volume effect we are unable to quantify the absolute changes in the local brain haemoglobin concentrations with NIRS and thus are unable to obtain an estimate of the absolute CMRO2 change. An absolute estimate is also confounded by uncertainty in the flow-volume relationship. However, the ratio of the flow change to the CMRO2 change is relatively insensitive to these uncertainties. For the linger tapping task, we estimate a most probable flow-consumption ratio ranging from 1.5 to 3 in agreement with previous findings presented in the literature, although we cannot exclude the possibility that there is no CMRO2 change. The large range in the ratio arises from the large number of model parameters that must be estimated from the data. A more precise estimate of the flow-consumption ratio will require better estimates of the model parameters or flow information, as can be provided by combining NIRS with fMRI.

Adult↗

PubMed2003

The Multi-Source Interference Task: validation study with fMRI in individual subjects.

Dorsal anterior cingulate cortex (dACC) plays critical roles in cognitive processing, but group-averaging techniques have generally been required to obtain significant dACC activation in functional neuroimaging studies. Development of a task that reliably and robustly activates dACC within individuals is needed to improve imaging studies of neuropsychiatric disorders and localization of dACC in normal volunteers. By combining sources of cognitive interference (Stroop, Eriksen and Simon) with factors known to increase dACC activity, the Multi-Source Interference Task (MSIT) maximally taxes dACC, making it possible to reliably activate dACC within individuals using functional magnetic resonance imaging (fMRI). In this study, eight normal adult volunteers performed the MSIT during fMRI. We compared fMRI responses and performance data between interference and control trials. Significant dACC activation (P < 1.7 x 10(-4)) was observed in all eight individuals and in the group-averaged fMRI data. In addition to dACC activation, group data also showed activation of presumably networked regions including dorsolateral prefrontal, premotor, and parietal cortices. The MSIT's reaction time interference effect (overall mean 312 +/- 61 ms) was up to 10 times greater than that of its component predecessors and temporally stable over hundreds of trials. The robustness, reliability and stability of the neuroimaging and performance data should make the MSIT a useful task with which to study normal human cognition and psychiatric pathophysiology.

Adult↗

PubMed2003

fMRI studies of associative encoding in young and elderly controls and mild Alzheimer's disease.

OBJECTIVE: To examine alterations in patterns of brain activation seen in normal aging and in mild Alzheimer's disease by functional magnetic resonance imaging (fMRI) during an associative encoding task. METHODS: 10 young controls, 10 elderly controls, and seven patients with mild Alzheimer's disease were studied using fMRI during a face-name association encoding task. The fMRI paradigm used a block design with three conditions: novel face-name pairs, repeated face-name pairs, and visual fixation. RESULTS: The young and elderly controls differed primarily in the pattern of activation seen in prefrontal and parietal cortices: elderly controls showed significantly less activation in both superior and inferior prefrontal cortices but greater activation in parietal regions than younger controls during the encoding of novel face-name pairs. Compared with elderly controls, the Alzheimer patients showed significantly less activation in the hippocampal formation but greater activation in the medial parietal and posterior cingulate regions. CONCLUSIONS: The pattern of fMRI activation during the encoding of novel associations is differentially altered in the early stages of Alzheimer's disease compared with normal aging.

Adult↗

PubMed2001

Visual motion processing investigated using contrast agent-enhanced fMRI in awake behaving monkeys.

To reduce the information gap between human neuroimaging and macaque physiology and anatomy, we mapped fMRI signals produced by moving and stationary stimuli (random dots or lines) in fixating monkeys. Functional sensitivity was increased by a factor of approximately 5 relative to the BOLD technique by injecting a contrast agent (monocrystalline iron oxide nanoparticle [MION]). Areas identified as motion sensitive included V2, V3, MT/V5, vMST, FST, VIP, and FEF (with moving dots), as well as V4, TE, LIP, and PIP (with random lines). These regions sensitive for moving dots are largely in agreement with monkey single unit data and (except for V3A) with human fMRI results. Moving lines activate some regions that have not been previously implicated in motion processing. Overall, the results clarify the relationship between the motion pathway and the dorsal stream in primates.

Animals↗

PubMed2001

Functional magnetic resonance imaging of reorganization in rat brain after stroke.

Functional recovery after stroke has been associated with brain plasticity; however, the exact relationship is unknown. We performed behavioral tests, functional MRI, and histology in a rat stroke model to assess the correlation between temporal changes in sensorimotor function, brain activation patterns, cerebral ischemic damage, and cerebrovascular reactivity. Unilateral stroke induced a large ipsilateral infarct and acute dysfunction of the contralateral forelimb, which significantly recovered at later stages. Forelimb impairment was accompanied by loss of stimulus-induced activation in the ipsilesional sensorimotor cortex; however, local tissue and perfusion were only moderately affected and cerebrovascular reactivity was preserved in this area. At 3 days after stroke, extensive activation-induced responses were detected in the contralesional hemisphere. After 14 days, we found reduced involvement of the contralesional hemisphere, and significant responses in the infarction periphery. Our data suggest that limb dysfunction is related to loss of brain activation in the ipsilesional sensorimotor cortex and that restoration of function is associated with biphasic recruitment of peri- and contralesional functional fields in the brain.

Animals↗

PubMed2001

Mechanisms of migraine aura revealed by functional MRI in human visual cortex.

Cortical spreading depression (CSD) has been suggested to underlie migraine visual aura. However, it has been challenging to test this hypothesis in human cerebral cortex. Using high-field functional MRI with near-continuous recording during visual aura in three subjects, we observed blood oxygenation level-dependent (BOLD) signal changes that demonstrated at least eight characteristics of CSD, time-locked to percept/onset of the aura. Initially, a focal increase in BOLD signal (possibly reflecting vasodilation), developed within extrastriate cortex (area V3A). This BOLD change progressed contiguously and slowly (3.5 +/- 1.1 mm/min) over occipital cortex, congruent with the retinotopy of the visual percept. Following the same retinotopic progression, the BOLD signal then diminished (possibly reflecting vasoconstriction after the initial vasodilation), as did the BOLD response to visual activation. During periods with no visual stimulation, but while the subject was experiencing scintillations, BOLD signal followed the retinotopic progression of the visual percept. These data strongly suggest that an electrophysiological event such as CSD generates the aura in human visual cortex.

Adult↗

PubMed2001

Regional sensitivity and coupling of BOLD and CBV changes during stimulation of rat brain.

Functional MRI of rat brain was performed at 2 Tesla following intravenous injection of cocaine in order to 1) determine if changes in CBV and changes in BOLD signal were regionally coupled in brain parenchyma, and 2) compare the sensitivities of these imaging methods across different brain structures. Percent changes in CBV and BOLD relaxation rate were spatially and temporally coupled during this graded brain activation. The use of contrast agent increased functional sensitivity in all parenchymal brain structures, with a strong but predictable dependence on the resting-state blood volume fraction. Magn Reson Med 45:443-447, 2001.

Animals↗

PubMed2001

Encoding novel face-name associations: a functional MRI study.

The process of forming new associations between previously unrelated items of information, such as a name and a face, likely requires the integration of activity within multiple brain regions. The hippocampus and related structures in the medial temporal lobe are thought to be particularly critical in binding together items of information. We studied eight healthy young subjects with functional magnetic resonance imaging (fMRI) during the encoding of novel face-name associations compared to viewing repeated face-name pairs. A consistent pattern of activation was observed in the hippocampus, pulvinar nucleus of the thalamus, fusiform and dorsolateral prefrontal cortices across individual subjects. The location of the activation within the hippocampus was more anterior than previously reported in studies using similar novel vs. repeated paradigms with stimuli that did not specifically require relational processing among unrelated items. These data suggest that the process of forming new face-name associations is supported by a distributed network of brain regions, and provide additional evidence for the essential role of the hippocampus in associative memory processes.

Adult↗

PubMed2001

Activation and habituation in olfaction--an fMRI study.

This study investigated human BOLD responses in primary and higher order olfactory cortices following presentation of short- and long-duration odorant stimuli using a 3-T MR scanner. The goal was to identify temporal differences in the course of the response that might underlie habituation. A short-duration stimulus (9 s) consistently activated the primary olfactory cortex (POC). After a long stimulus (60 s), the temporal form of the response differed in different parts of the olfactory network: (1) The POC (piriform, entorhinal cortex, amygdala) and, interestingly, the hippocampus and, to a certain degree, the anterior insula show a short, phasic increase in the signal, followed by a prolonged decrease below baseline. (2) In the orbitofrontal cortex a sustained increase in activation was seen. This increase lasted approximately as long as the duration of odorant presentation ( approximately 60 s). (3) The mediodorsal nucleus of the thalamus and the caudate nucleus responded with an increase in signal which returned to baseline after approximately 15 to 30 s. The correlated biphasic hemodynamic response in the POC, hippocampus, and anterior insula during prolonged olfactory stimulation suggests that these three areas may interact closely with each other in the control of habituation. These results extend recent data which showed habituation of the rat piriform cortex and dissociation between the POC and the orbitofrontal cortex.

Adult↗

PubMed2001

Cortical mechanisms specific to explicit visual object recognition.

The cortical mechanisms associated with conscious object recognition were studied using functional magnetic resonance imaging (fMRI). Participants were required to recognize pictures of masked objects that were presented very briefly, randomly and repeatedly. This design yielded a gradual accomplishment of successful recognition. Cortical activity in a ventrotemporal visual region was linearly correlated with perception of object identity. Therefore, although object recognition is rapid, awareness of an object's identity is not a discrete phenomenon but rather associated with gradually increasing cortical activity. Furthermore, the focus of the activity in the temporal cortex shifted anteriorly as subjects reported an increased knowledge regarding identity. The results presented here provide new insights into the processes underlying explicit object recognition, as well as the analysis that takes place immediately before and after recognition is possible.

Adult↗

PubMed2001

Delayed rt-PA treatment in a rat embolic stroke model: diagnosis and prognosis of ischemic injury and hemorrhagic transformation with magnetic resonance imaging.

The authors characterized effects of late recombinant tissue plasminogen activator (rt-PA) administration in a rat embolic stroke model with magnetic resonance imaging (MRI), to assess potential MRI correlates, or predictors, or both, of rt-PA-induced hemorrhage. Diffusion-, perfusion-, and postcontrast T1-weighted MRI were performed between 4 and 9 hours and at 24 hours after embolic stroke in spontaneously hypertensive rats. Treatment with either rt-PA or saline was started 6 hours after stroke. A spectrophotometric hemoglobin assay quantified hemorrhage severity. Before treatment, relative cerebral blood flow index (rCBFi) and apparent diffusion coefficient (ADC) in the ischemic territory were 30% +/- 23% and 60% +/- 5% (of contralateral), respectively, which increased to 45% +/- 39% and 68% +/- 4% 2 hours after rt-PA. After 24 hours, rCBFi and ADC were 27% +/- 27% and 59 +/- 5%. Hemorrhage volume after 24 hours was significantly greater in rt-PA-treated animals than in controls (8.7 +/- 3.7 microL vs. 5.1 +/- 2.4 microL, P < 0.05). Before rt-PA administration, clear postcontrast T1-weighted signal intensity enhancement was evident in areas of subsequent bleeding. These areas had lower rCBFi levels than regions without hemorrhage (23% +/- 22% vs. 36% +/- 29%, P < 0.05). In conclusion, late thrombolytic therapy does not necessarily lead to successful reperfusion. Hemorrhage emerged in areas with relatively low perfusion levels and early blood-brain barrier damage. Magnetic resonance imaging may be useful for quantifying effects of thrombolytic therapy and predicting risks of hemorrhagic transformation.

Animals↗

PubMed2001

Predicting tissue outcome in acute human cerebral ischemia using combined diffusion- and perfusion-weighted MR imaging.

BACKGROUND AND PURPOSE: Tissue signatures from acute MR imaging of the brain may be able to categorize physiological status and thereby assist clinical decision making. We designed and analyzed statistical algorithms to evaluate the risk of infarction for each voxel of tissue using acute human functional MRI. METHODS: Diffusion-weighted MR images (DWI) and perfusion-weighted MR images (PWI) from acute stroke patients scanned within 12 hours of symptom onset were retrospectively studied and used to develop thresholding and generalized linear model (GLM) algorithms predicting tissue outcome as determined by follow-up MRI. The performances of the algorithms were evaluated for each patient by using receiver operating characteristic curves. RESULTS: At their optimal operating points, thresholding algorithms combining DWI and PWI provided 66% sensitivity and 83% specificity, and GLM algorithms combining DWI and PWI predicted with 66% sensitivity and 84% specificity voxels that proceeded to infarct. Thresholding algorithms that combined DWI and PWI provided significant improvement to algorithms that utilized DWI alone (P=0.02) but no significant improvement over algorithms utilizing PWI alone (P=0.21). GLM algorithms that combined DWI and PWI showed significant improvement over algorithms that used only DWI (P=0.02) or PWI (P=0.04). The performances of thresholding and GLM algorithms were comparable (P>0.2). CONCLUSIONS: Algorithms that combine acute DWI and PWI can assess the risk of infarction with higher specificity and sensitivity than algorithms that use DWI or PWI individually. Methods for quantitatively assessing the risk of infarction on a voxel-by-voxel basis show promise as techniques for investigating the natural spatial evolution of ischemic damage in humans.

Acute Disease↗

PubMed2001

Changes in motor cortex activation after recovery from spinal cord inflammation.

Diseases of the spinal cord are associated with reactive changes in cerebral cortex organization. Many studies in this area have examined spinal cord conditions not associated with recovery, making it difficult to consider the value of these cortical events in the restoration of neurological function. We studied patients with myelitis, a syndrome of transient spinal cord inflammation, in order to probe cortical changes that might contribute to recovery after disease of the spinal cord. Seven patients, each of whom showed improvement in hand motor function after a diagnosis of myelitis involving cervical spinal cord, were clinically evaluated then studied with functional MRI. During right and left index finger tapping, activation volumes were assessed in three cortical motor regions within each hemisphere. Results were compared with findings in nine control subjects. Compared to the control group, myelitis patients had larger activation volumes within contralateral sensorimotor as well as contralateral premotor cortex. The degree of daily hand use showed a significant correlation with the volume of activation in contralateral sensorimotor cortex. Recovery from myelitis is associated with an enlarged activation volume in contralateral motor cortices. This change in motor cortex function is related to behavioral experience, and thus may contribute to motor improvement. The expanded activation in motor cortex, seen with several forms of spinal cord insult may have maximal utility when corticospinal tract axons are preserved.

Adult↗

PubMed2001

A functional MRI study of three motor tasks in the evaluation of stroke recovery.

Functional brain imaging studies have provided insights into the processes related to motor recovery after stroke. The comparative value of different motor activation tasks for probing these processes has received limited study. We hypothesized that different hand motor tasks would activate the brain differently in controls, and that this would affect control-patient comparisons. Functional magnetic resonance imaging (MRI) was used to evaluate nine control subjects and seven patients with good recovery after a left hemisphere hemiparetic stroke. The volume of activated brain in bilateral sensorimotor cortex and four other motor regions was compared during each of three tasks performed by the right hand: index-finger tapping, four-finger tapping, and squeezing. In control subjects, activation in left sensorimotor cortex was found to be significantly larger during squeezing as compared with index-finger tapping. When comparing control subjects with stroke patients, patients showed a larger volume of activation in right sensorimotor cortex during index-finger tapping but not with four-finger tapping or squeezing. In addition, patients also showed a trend toward larger activation volume than controls within left supplementary motor area during index-finger tapping but not during the other tasks. Motion artifact was more common with squeezing than with the tapping tasks. The choice of hand motor tasks used during brain mapping can influence findings in control subjects as well as the differences identified between controls and stroke patients. The results may be useful for future studies of motor recovery after stroke.

Adult↗

PubMed2000

Laterality, somatotopy and reproducibility of the basal ganglia and motor cortex during motor tasks.

We investigated the basal ganglia, motor cortex area 4, and supplementary motor area (SMA) using functional magnetic resonance imaging (fMRI) and five motor tasks: switching between finger and toe movements, writing, finger tapping, pronation/supination, and saccadic eye movements. We found reliable activation in the caudate nucleus and putamen in single subjects without the need for inter-subject averaging. Percent signal changes in basal ganglia were smaller by a factor of three than those in SMA or motor cortex (1% vs. 2.5-3%). There was a definite foot-dorsal, hand-ventral basal ganglia somatotopy, similar to prior data from primates. Saccadic eye movements activated the caudate nucleus significantly more than the other tasks did. Unilateral movements produced bilateral activation in the striatum even when motor cortex activation was unilateral. Surprisingly, bilateral performance of the tasks led, on average, to consistently smaller basal ganglia activation than did unilateral performance (P<0.001), suggesting less inhibition of contralateral movements during bilateral tasks. Moreover, there was a striking dominance pattern in basal ganglia motor activation: the left basal ganglia were more active than the right for right handers, regardless of the hand used. This lateralization appears much stronger than that previously reported for motor cortex. Comparisons of inter-subject and intra-subject reproducibility indicated a much larger variability in basal ganglia and SMA compared to motor cortex, in spite of similar percent signal changes in the latter two structures.

Adult↗