David F. Abbott

Amygdala Responses to Fearful and Happy Facial Expressions under Conditions of Binocular Suppression

The human amygdala plays a crucial role in processing affective information conveyed by sensory stimuli. Facial expressions of fear and anger, which both signal potential threat to an observer, result in significant increases in amygdala activity, even when the faces are unattended or presented briefly and masked. It has been suggested that afferent signals from the retina travel to the amygdala via separate cortical and subcortical pathways, with the subcortical pathway underlying unconscious processing. Here we exploited the phenomenon of binocular rivalry to induce complete suppression of affective face stimuli presented to one eye. Twelve participants viewed brief, rivalrous visual displays in which a fearful, happy, or neutral face was presented to one eye while a house was presented simultaneously to the other. We used functional magnetic resonance imaging to study activation in the amygdala and extrastriate visual areas for consciously perceived versus suppressed face and house stimuli. Activation within the fusiform and parahippocampal gyri increased significantly for perceived versus suppressed faces and houses, respectively. Amygdala activation increased bilaterally in response to fearful versus neutral faces, regardless of whether the face was perceived consciously or suppressed because of binocular rivalry. Amygdala activity also increased significantly for happy versus neutral faces, but only when the face was suppressed. This activation pattern suggests that the amygdala has a limited capacity to differentiate between specific facial expressions when it must rely on information received via a subcortical route. We suggest that this limited capacity reflects a tradeoff between specificity and speed of processing.

Functional connectivity networks are disrupted in left temporal lobe epilepsy

Functional connectivity maps the distributed network of brain regions fluctuating synchronously during a continuous brain state. This study sought to investigate whether patients with left temporal lobe epilepsy (TLE) differ from controls in their resting‐state functional connectivity between typical language regions.

Effect of prior cognitive state on resting state networks measured with functional connectivity.

To address the extent to which functional connectivity measures an absolute brain state, we observed the effect of prior performance of a language task on resting‐state networks in regions associated with language. Six subjects were imaged during rest before and after a block‐design language task. Connectivity maps were generated for each of four language regions (identified from analysis of the language activation portion of the study) in each subject for both rest periods. Conjunction analysis demonstrated distinct networks of voxels for each seed region, indicating separate functional subnetworks associated with the different regions. In a comparison of rest before and after the activation task widespread and significant changes were observed in all individuals, suggesting that the measured resting state network reflects a dynamic image of the current brain state. At the group level, an extended network was observed that was largely persistent over time. Even at the group level an increase in connectivity was observed between left and right middle frontal gyri, and between posterior cingulate cortex and medial frontal cortex in the rest after the language task. These results suggest that functional connectivity may be a powerful measure of cognitive state, sensitive to differences between controls and patients together with the particular cognitive processing occurring during the rest state. Hum. Brain Mapping 24:59–68, 2005.

Viewing the motion of human body parts activates different regions of premotor, temporal, and parietal cortex

Activation of premotor and temporoparietal cortex occurs when we observe others movements, particularly relating to objects. Viewing the motion of different body parts without the context of an object has not been systematically evaluated. During a 3T fMRI study, 12 healthy subjects viewed human face, hand, and leg motion, which was not directed at or did not involve an object. Activation was identified relative to static images of the same human face, hand, and leg in both individual subject and group average data. Four clear activation foci emerged: (1) right MT/V5 activated to all forms of viewed motion; (2) right STS activated to face and leg motion; (3) ventral premotor cortex activated to face, hand, and leg motion in the right hemisphere and to leg motion in the left hemisphere; and (4) anterior intraparietal cortex (aIP) was active bilaterally to viewing hand motion and in the right hemisphere leg motion. In addition, in the group data, a somatotopic activation pattern for viewing face, hand, and leg motion occurred in right ventral premotor cortex. Activation patterns in STS and aIP were more complex--typically activation foci to viewing two types of human motion showed some overlap. Activation in individual subjects was similar; however, activation to hand motion also occurred in the STS with a variable location across subjects--explaining the lack of a clear activation focus in the group data. The data indicate that there are selective responses to viewing motion of different body parts in the human brain that are independent of object or tool use.

Identifying hypoxic tissue after acute ischemic stroke using PET and 18F-fluoromisonidazole

Objective: To show that PET with 18F-fluoromisonidazole (18F-FMISO) can detect peri-infarct hypoxic tissue in patients after ischemic stroke. Background: PET with 15O-labeled oxygen and water is the only established method for identifying the ischemic penumbra in humans. We used PET with 18F-FMISO in patients after ischemic stroke to identify hypoxic but viable peri-infarct tissue likely to represent the ischemic penumbra, and to determine how long hypoxic tissues persist after stroke. Methods: Patients with acute hemispheric ischemic stroke were studied using PET with 18F-FMISO either within 48 hours or 6 to 11 days after stroke onset. The final infarct was defined by CT performed 6 to 11 days after stroke. Tracer uptake was assessed objectively by calculating the mean activity in the contralateral (normal) hemisphere, then identifying pixels with activity greater than 3 SDs above the mean in both hemispheres. Positive studies were those with high-activity pixels ipsilateral to the infarct. Results: Fifteen patients were studied; 13 within 48 hours of stroke, 8 at 6 to 11 days, and 6 during both time periods. Hypoxic tissue was detected in 9 of the 13 patients studied within 48 hours of stroke, generally distributed in the peripheries of the infarct and adjacent peri-infarct tissues. None of the 8 patients studied 6 to 11 days after stroke exhibited increased 18F-FMISO activity. All 6 patients studied both early and late exhibited areas of increased activity during the early but not the late study. Conclusions: PET with 18F-FMISO can detect peri-infarct hypoxic tissue after acute ischemic stroke. The distribution of hypoxic tissue suggests that it may represent the ischemic penumbra. Hypoxic tissues do not persist to the subacute phase of stroke (6 to 11 days).

The fate of hypoxic tissue on 18F-fluoromisonidazole positron emission tomography after ischemic stroke.

We studied 24 patients up to 51 hours after ischemic stroke using 18F‐fluoromisonidazole positron emission tomography to determine the fate of hypoxic tissue likely to represent the ischemic penumbra. Areas of hypoxic tissue were detected on positron emission tomography in 15 patients, and computed tomography was available in 12 patients, allowing comparison with the infarct volume to determine the proportions of the hypoxic tissue volume that infarcted and survived. The proportion of patients with hypoxic tissue and the amount of hypoxic tissue detected declined with time. On average, 45% of the total hypoxic tissue volume survived and 55% infarcted. Up to 68% (mean, 17.5%) of the infarct volume was initially hypoxic. Most of the tissue “initially affected” proceeded to infarction. We correlated hypoxic tissue volumes with neurological and functional outcome assessed using the National Institutes of Health Stroke Scale, Barthel Index, and Rankin Score. Initial stroke severity correlated significantly with the “initially affected” volume, neurological deterioration during the first week after stroke with the proportion of the “initially affected” volume that infarcted, and functional outcome with the infarct volume. Significant reductions in the size of the infarct and improved clinical outcomes might be achieved if hypoxic tissue can be rescued. Ann Neurol 2000;48:228–235

Randomized trial of constraint-induced movement therapy and bimanual training on activity outcomes for children with congenital hemiplegia

Aim  To determine if constraint‐induced movement therapy (CIMT) is more effective than bimanual training (BIM) in improving upper limb activity outcomes for children with congenital hemiplegia in a matched‐pairs randomized trial.

Hippocampal volume assessment in temporal lobe epilepsy: How good is automated segmentation?

Purpose:  Quantitative measurement of hippocampal volume using structural magnetic resonance imaging (MRI) is a valuable tool for detection and lateralization of mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE). We compare two automated hippocampal volume methodologies and manual hippocampal volumetry to determine which technique is most sensitive for the detection of hippocampal atrophy in mTLE.

The human temporal lobe integrates facial form and motion: evidence from fMRI and ERP studies.

Physiological studies in humans and monkeys indicate that the posterior temporal cortex is active when viewing the movements of others. Here we tested the premise that this region integrates form and motion information by presenting both natural and line-drawn displays of moving faces and motion controls where motion was continuously presented in the same part of the visual field. The cortex in and near the STS and on the fusiform gyrus (FG) responded to both types of face stimuli, but not to the controls, in a functional magnetic resonance imaging study in 10 normal subjects. The response in the STS to both types of facial motion was equal in magnitude, whereas in the FG the natural image of the face produced a significantly greater response than that of the line-drawn face. In a subsequent recording session, the electrical activity of the brain was recorded in the same subjects to the same activation task. Significantly larger event-related potentials (ERPs) to both types of moving faces were observed over the posterior temporal scalp compared to the motion controls at around 200 ms postmotion onset. Taken together, these data suggest that regions of temporal cortex actively integrate form and motion information-a process largely independent of low-level visual processes such as changes in local luminance and contrast.

Cortical/subcortical BOLD changes associated with epileptic discharges: An EEG-fMRI study at 3 T

Background: Malformations of cortical development have characteristic interictal discharges, yet the mechanisms of generation of these discharges are not known in humans. Interictal discharges in malformations of cortical development were studied with EEG-fMRI. Methods: Six subjects with malformations of cortical development and seizures were studied using spike-triggered fMRI at 3 T. The blood oxygen level–dependent (BOLD) signal changes associated with interictal discharges were measured. Results: All subjects showed spike-related BOLD signal changes. In four subjects, the signal increases were seen in the lesion, and in four subjects, decreases were seen surrounding the lesion. Five subjects had BOLD signal changes at distant cortical sites and three had subcortical changes (basal ganglia, reticular formation, or thalamic). Conclusion: BOLD signal changes may be directly correlated with overall synaptic activity. Changes were found in and around the lesion of malformations of cortical development and in distant cortical and subcortical structures. The results suggest that EEG-fMRI studies might help elucidate the mechanisms of epileptic discharges in humans.