Mark S. Cohen

PATTERNS OF BRAIN ACTIVATION IN PEOPLE AT RISK FOR ALZHEIMER’S DISEASE

BACKGROUND The epsilon4 allele of the apolipoprotein E gene (APOE) is the chief known genetic risk factor for Alzheimers disease, the most common cause of dementia late in life. To determine the relation between brain responses to tasks requiring memory and the genetic risk of Alzheimers disease, we performed APOE genotyping and functional magnetic resonance imaging (MRI) of the brain in older persons with intact cognition. METHODS We studied 30 subjects (age, 47 to 82 years) who were neurologically normal, of whom 16 were carriers of the APOE epsilon4 allele and 14 were homozygous for the APOE epsilon3 allele. The mean age and level of education were similar in the two groups. Patterns of brain activation during functional MRI scanning were determined while subjects memorized and recalled unrelated pairs of words and while subjects rested between such periods. Memory was reassessed in 14 subjects two years later. RESULTS Both the magnitude and the extent of brain activation during memory-activation tasks in regions affected by Alzheimers disease, including the left hippocampal, parietal, and prefrontal regions, were greater among the carriers of the APOE epsilon4 allele than among the carriers of the APOE epsilon3 allele. During periods of recall, the carriers of the APOE epsilon4 allele had a greater average increase in signal intensity in the hippocampal region (1.03 percent vs. 0.62 percent, P<0.001) and a greater mean (+/-SD) number of activated regions throughout the brain (15.9+/-6.2 vs. 9.4+/-5.5, P=0.005) than did carriers of the APOE epsilon3 allele. Longitudinal assessment after two years indicated that the degree of base-line brain activation correlated with degree of decline in memory. CONCLUSIONS Patterns of brain activation during tasks requiring memory differ depending on the genetic risk of Alzheimers disease and may predict a subsequent decline in memory.

Parametric Analysis of fMRI Data Using Linear Systems Methods

Using a model of the functional MRI (fMRI) impulse response based on published data, we have demonstrated that the form of the fMRI response to stimuli of freely varied timing can be modeled well by convolution of the impulse response with the behavioral stimulus. The amplitudes of the responses as a function of parametrically varied behavioral conditions are fitted well using a piecewise linear approximation. Use of the combined model, in conjunction with correlation analysis, results in an increase in sensitivity for the MRI study. This approach, based on the well-established methods of linear systems analysis, also allows a quantitative comparison of the response amplitudes across subjects to a broad range of behavioral conditions. Fit parameters, derived from the amplitude data, are relatively insensitive to a variety of MRI-related artifacts and yield results that are compared readily across subjects.

Acquiring simultaneous EEG and functional MRI

OBJECTIVE Electroencephalography (EEG) is a challenge to record simultaneously with functional MRI (fMRI), for it is prone to large artifacts induced by both the static and the time-variant fields of the MR scanner. However, truly concurrent EEG/fMRI recording has great potential for clinical and scientific neurological applications. We have devised a method for acquiring EEG simultaneously with fMRI that minimizes contamination of the EEG signals. METHODS We recorded EEG differentially during fMRI using special twisted dual-lead electrodes in a bipolar montage, and a combination of analog pre-processing and digital post-processing of the EEG data. We implemented a functional scan protocol that typically yields artifact-free EEG over 87% of the MR scanning period. RESULTS Our approach greatly reduced gradient, radio frequency, motion and ballistocardiographic artifact in the EEG, and allowed continuous monitoring of the EEG during functional scanning. To illustrate the quality of the EEG following post-processing, we demonstrated that EEG recorded during fMRI retains useful spectral information. CONCLUSIONS Quality EEG may be recorded simultaneously with fMRI. With this union, activation maps could be made of any relevant changes in the EEG, such as inter-ictal spikes or spectral variations, or of evoked response potentials (ERPs).

Rotatory Instability of the Elbow. The Anatomy and Role of the Lateral Stabilizers

Posterolateral rotatory instability of the elbow has been attributed to disruption of the ulnar part of the lateral collateral ligament. Forty fresh cadavera were studied to define the ligamentous anatomy of the lateral aspect of the elbow specifically as it relates to rotatory instability. The dissections revealed a broad conjoined insertion of the lateral collateral and annular ligaments onto the proximal aspect of the ulna. This insertion was bilobed (type I) in twenty-two specimens and broad (type II) in eighteen specimens. Serial sectioning studies revealed primary and secondary stabilizers of the lateral aspect of the elbow. In addition to the lateral collateral ligament and the annular ligament, the extensor muscle origins provide stability through fascial bands and intermuscular septa. CLINICAL RELEVANCE: The findings of this study suggest that post-traumatic posterolateral rotatory instability of the elbow is the result of attenuation or disruption of both the ligamentous and the muscular origins from the lateral epicondyle of the humerus. Injury to these structures should be avoided during operative exposures for procedures such as débridement of the elbow for recalcitrant lateral epicondylitis, resection of the radial head, or capsular release for a stiff elbow. If immobilization is necessary postoperatively, the forearm should be held in pronation.

Localization of brain function using magnetic resonance imaging

When nuclear magnetic resonance images (MRIs) of the brain are acquired in rapid succession they exhibit small differences in signal intensity in positions corresponding to focal areas of activation. These signal changes result from small differences in the magnetic resonance signal caused by variations in the oxygenation state of the venous vasculature. Using this non-invasive functional MRI (fMRI) method, it is possible to localize functional brain activation, in normal individuals, with an accuracy of millimeters and a temporal resolution of seconds. Though numerous technical challenges remain, fMRI is increasingly becoming a key method for understanding the topographical organization of the human brain.

Neural Substrates of Resisting Craving during Cigarette Cue Exposure

BACKGROUND In cigarette smokers, the most commonly reported areas of brain activation during visual cigarette cue exposure are the prefrontal, anterior cingulate, and visual cortices. We sought to determine changes in brain activity in response to cigarette cues when smokers actively resist craving. METHODS Forty-two tobacco-dependent smokers underwent functional magnetic resonance imaging, during which they were presented with videotaped cues. Three cue presentation conditions were tested: cigarette cues with subjects allowing themselves to crave (cigarette cue crave), cigarette cues with the instruction to resist craving (cigarette cue resist), and matched neutral cues. RESULTS Activation was found in the cigarette cue resist (compared with the cigarette cue crave) condition in the left dorsal anterior cingulate cortex (ACC), posterior cingulate cortex (PCC), and precuneus. Lower magnetic resonance signal for the cigarette cue resist condition was found in the cuneus bilaterally, left lateral occipital gyrus, and right postcentral gyrus. These relative activations and deactivations were more robust when the cigarette cue resist condition was compared with the neutral cue condition. CONCLUSIONS Suppressing craving during cigarette cue exposure involves activation of limbic (and related) brain regions and deactivation of primary sensory and motor cortices.

Blunted activation in orbitofrontal cortex during mania : A functional magnetic resonance imaging study

BACKGROUND Patients with bipolar disorder have been reported to have abnormal cortical function during mania. In this study, we sought to investigate neural activity in the frontal lobe during mania, using functional magnetic resonance imaging (fMRI). Specifically, we sought to evaluate activation in the lateral orbitofrontal cortex, a brain region that is normally activated during activities that require response inhibition. METHODS Eleven manic subjects and 13 control subjects underwent fMRI while performing the Go-NoGo task, a neuropsychological paradigm known to activate the orbitofrontal cortex in normal subjects. Patterns of whole-brain activation during fMRI scanning were determined with statistical parametric mapping. Contrasts were made for each subject for the NoGo minus Go conditions. Contrasts were used in a second-level analysis with subject as a random factor. RESULTS Functional MRI data revealed robust activation of the right orbitofrontal cortex (Brodmanns area [BA] 47) in control subjects but not in manic subjects. Random-effects analyses demonstrated significantly less magnitude in signal intensity in the right lateral orbitofrontal cortex (BA 47), right hippocampus, and left cingulate (BA 24) in manic compared with control subjects. CONCLUSIONS Mania is associated with a significant attenuation of task-related activation of right lateral orbitofrontal function. This lack of activation of a brain region that is usually involved in suppression of responses might account for some of the disinhibition seen in mania. In addition, hippocampal and cingulate activation seem to be decreased. The relationship between this reduced function and the symptoms of mania remain to be further explored.

Qualitative and quantitative evaluation of six algorithms for correcting intensity nonuniformity effects.

The desire to correct intensity nonuniformity in magnetic resonance images has led to the proliferation of nonuniformity-correction (NUC) algorithms with different theoretical underpinnings. In order to provide end users with a rational basis for selecting a given algorithm for a specific neuroscientific application, we evaluated the performance of six NUC algorithms. We used simulated and real MRI data volumes, including six repeat scans of the same subject, in order to rank the accuracy, precision, and stability of the nonuniformity corrections. We also compared algorithms using data volumes from different subjects and different (1.5T and 3.0T) MRI scanners in order to relate differences in algorithmic performance to intersubject variability and/or differences in scanner performance. In phantom studies, the correlation of the extracted with the applied nonuniformity was highest in the transaxial (left-to-right) direction and lowest in the axial (top-to-bottom) direction. Two of the six algorithms demonstrated a high degree of stability, as measured by the iterative application of the algorithm to its corrected output. While none of the algorithms performed ideally under all circumstances, locally adaptive methods generally outperformed nonadaptive methods.

Norian SRS cement compared with conventional fixation in distal radial fractures. A randomized study.

BACKGROUND A prospective, randomized multicenter study was conducted to evaluate closed reduction and immobilization with and without Norian SRS (Skeletal Repair System) cement in the management of distal radial fractures. Norian SRS is a calcium-phosphate bone cement that is injectable, hardens in situ, and cures by a crystallization reaction to form dahllite, a carbonated apatite equivalent to bone mineral. METHODS A total of 323 patients with a distal radial fracture were randomized to treatment with or without Norian SRS cement. Stratification factors included fracture type (intra-articular or extra-articular), hand dominance, bone density, and the surgeons preferred conventional treatment (cast or external fixator). The subjects receiving Norian SRS underwent a closed reduction followed by injection of the cement percutaneously or through a limited open approach. Wrist motion, beginning two weeks postoperatively, was encouraged. Control subjects, who had not received a Norian SRS injection, underwent closed reduction and application of a cast or external fixator for six to eight weeks. Supplemental Kirschner wires were used in specific instances in both groups. Patients were followed clinically and radiographically at one, two, four, and between six and eight weeks and at three, six, and twelve months. Patients rated pain and the function of the hand with use of a visual analog scale. Quality of life was assessed with use of the Short Form-36 (SF-36) health status questionnaire. Complications were recorded. RESULTS Significant clinical differences were seen at six to eight weeks postoperatively, with better grip strength, wrist range of motion, digital motion, use of the hand, and social and emotional function, and less swelling in the patients treated with Norian SRS than in the control group (p < 0.05). By three months, these differences had normalized except for digital motion, which remained significantly better in the group treated with Norian SRS (p = 0.015). At one year, no clinical differences were detected. Radiographically, the average change in ulnar variance was greater in the patients treated with Norian SRS (+2.0 mm) than in the control group (+1.4 mm) (p < 0.02). No differences were seen in the total number of complications, including loss of reduction. The infection rate, however, was significantly higher (p < 0.001) in the control group (16.7%) than in the group treated with Norian SRS (2.5%) and the infections were always related to external fixator pins or Kirschner wires. Four patients with intra-articular extravasation of cement were identified; no sequelae were observed at twenty-four months. Cement was seen in extraosseous locations in 112 (70%) of the SRS-treated patients; loss of reduction was highest in this subgroup (37%). The extraosseous material had disappeared in eighty-three of the 112 patients by twelve months. CONCLUSIONS Our results indicate that fixation of a distal radial fracture with Norian SRS cement may allow for accelerated rehabilitation. A limited open approach and supplemental fixation with Kirschner wires are recommended. Additional or alternate fixation is necessary for complex articular fractures.

Rapid and effective correction of rf inhomogeneity for high field magnetic resonance imaging

The well‐known variability in the distribution of high frequency electromagnetic fields in the human body causes problems in the analysis of structural information in high field magnetic resonance images. We describe a method of compensating for the purely intensity‐based effects. In our simple and rapid correction algorithm, we first use statistical means to determine the background image noise level and the edges of the image features. We next populate all “noise” pixels with the mean signal intensity of the image features. These data are then smoothed by convolution with a gaussian filter using Fourier methods. Finally, the original data that are above the noise level are normalized to the smoothed images, thereby eliminating the lowest spatial frequencies in the final, corrected data. Processing of a 124 slice, 256 × 256 volume dataset requires under 70 sec on a laptop personal computer. Overall, the method is less prone to artifacts from edges or from sensitivity to absolute head position than are other correction techniques. Following intensity correction, the images demonstrated obvious qualitative improvement and, when subjected to automated segmentation tools, the accuracy of segmentation improved, in one example, from 35.3% to 84.7% correct, as compared to a manually‐constructed gold standard. Hum. Brain Mapping 10:204–211, 2000.