Biomedical subjects

Mark S Cohen

Publications and source records attributed to Mark S Cohen.

At least 19 recordsLinked to original sources

PubMed2007

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.

Adult↗

PubMed2006

Effect of cigarette smoking on prefrontal cortical function in nondeprived smokers performing the Stroop Task.

Some reports indicate that cigarette smoking can help smokers focus attention, even when they have not abstained from smoking for a substantial period of time (eg, >1 h). Understanding the mechanisms by which smoking affects attention may help in designing smoking cessation treatments. Thirteen nonsmokers and nine smokers participated in two tests of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). During fMRI, the participants performed the Stroop Task. There was a 15-min break between the two tests. During the break, each smoker smoked one cigarette. For smokers, the first test began 45-60 min after the last cigarette of ad libitum smoking. The differences in BOLD signal changes between Stroop conditions (ie, incongruent minus congruent) showed a group x test interaction in the right precentral sulcus, including the putative human frontal eye field (FEF). Smokers, but not nonsmokers, showed greater changes (relative to rest) in BOLD signal in the incongruent than in the congruent condition in the first fMRI test but not in the second. Even after brief abstinence from smoking, therefore, smokers exhibit compromised functional efficiency in the right FEF and adjacent precentral sulcus in a test of selective attention; and smoking ameliorates this condition.

Adolescent↗

PubMed2006

Effects of acute smoking on brain activity vary with abstinence in smokers performing the N-Back task: a preliminary study.

We previously reported that compared with a non-deprivation state, overnight abstinence from cigarette smoking was associated with higher brain activity in the left dorsolateral prefrontal cortex (L-DLPFC) during a low demanding working memory challenge, and little increase beyond this activity level during more taxing working memory conditions. In the present study, we aimed to assess how recent smoking (overnight abstinence vs. smoking ad libitum) influenced the effect of smoking a cigarette on brain activity related to a working memory challenge. Six smokers performed the N-Back working memory task during functional magnetic resonance imaging (fMRI) both before and after smoking a cigarette in each of two test sessions: one following overnight abstinence from smoking ( approximately 13 h) and the other following ad libitum smoking. Task-related activity in L-DLPFC showed a significant interaction between the effects of acute smoking, test session, and task load. After overnight abstinence, post-smoking brain activity in L-DLPFC was lower than before smoking at low task load and higher at high task load; corresponding activity on a day of ad libitum smoking was higher at low load and lower at high task load after smoking during the session. These data suggest that the effect of acute smoking on working memory processing depends on recent prior smoking and task load. In particular, they provide preliminary evidence that functional efficiency of working memory is improved by smoking a cigarette during abstinence, while the effect of a cigarette in a non-deprived state varies with the nature and difficulty of the working memory challenge. This interaction merits further examination in larger studies specifically designed to consider this issue.

Adult↗

PubMed2006

The relationship between performance and fMRI signal during working memory in patients with schizophrenia, unaffected co-twins, and control subjects.

While behavioral research shows working memory impairments in schizophrenics and their relatives, functional neuroimaging studies of patients and healthy controls show conflicting findings of hypo- and hyperactivation, possibly indicating different relationships between physiological activity and performance. In a between-subjects regression analysis of fMRI activation and performance, low performance was associated with relatively lower activation in patients than controls, while higher performance was associated with higher activation in patients than controls in DLPFC and parietal cortex, but not occipital cortex, with unaffected twins of schizophrenics being intermediate between the groups. Accordingly, this supports the idea that both hyper and hypoactivation may be possible along a continuum of behavioral performance in a way consistent with a neural inefficiency model. Further, this study offers preliminary evidence that the relationship between behavior and physiology in schizophrenia may be heritable.

Aged↗

PubMed2006

Articular cartilage injuries of the capitellum interposed in radial head fractures: a report of ten cases.

Ten cases of Mason type I and type II isolated radial head fractures are reported, in which an unexpected cartilaginous fragment of the capitellum trapped within the radial head fracture was identified at the time of surgery. In no case was this injury pattern identified on preoperative imaging, including computed tomography in 2 cases. Five patients did have preoperative mechanical findings with forearm rotation. At surgery, all capitellar fragments were found to originate from the posterolateral capitellum. Excision of the capitellar fragment and internal fixation of the radial head fracture were performed in all cases. No sequelae were identified on short-term follow-up. This series highlights an injury pattern that should be considered in isolated nondisplaced and minimally displaced fractures of the radial head. The natural history of this finding, when treated conservatively, is unknown.

Adolescent↗

PubMed2006

Osseous anatomy of the distal humerus and proximal ulna: implications for total elbow arthroplasty.

Cortical thickness and multiple intramedullary canal diameters were measured in sequential axial sections from 27 human cadavers. No age or side differences were identified. The intramedullary humeral canal shape changed along the length of the bone in both male specimens and female specimens. Anteroposterior and male minimal humeral canal diameters increased proximally from the elbow. Male and female medial-lateral humeral diameters decreased proximally from the elbow. All ulnar canal diameters decreased distally in a uniform fashion. The minimal ulnar and humeral canal diameters did not occur in either the sagittal or coronal plane. Humeral and ulnar cortical thickness did not vary within axial sections. Only ulnar cortical thickness changed between sections, decreasing distally. On the basis of these data, a cylindrical humeral stem and an ulnar stem tapering in all planes may be optimal for total elbow arthroplasty stems. The relatively thin cortices of both the humerus and the ulna predispose patients to perforation, periarticular fracture, and complications during revision arthroplasty surgery. Finally, routine frontal and lateral radiographs may overestimate minimal canal size for total elbow arthroplasty components. However, the lateral view appears to approximate the true minimal canal diameter more closely.

Aged↗

PubMed2006

Effects of implant material and plate design on tendon function and morphology.

Titanium implants are an alternative to stainless steel implants for internal fixation after fracture. The advantages of titanium include decreased implant stiffness, increased bio-compatibility, and diminished stress shielding. However, titanium has been implicated in tendon irritation and adhesions when used in the hand and wrist. We evaluated the relationship between extensor tendon morphology and dorsal plating of the distal radius in a canine model using distal radius pi plates made of stainless steel, titanium, and titanium alloy with a modified ramped edge design. We found marked histologic changes in the tendons and surrounding soft tissues including tendon deformation and degeneration (fibrillation, cartilage metaplasia, hypocellularity and hyalinization of blood vessels), peritendonous adhesions and neovascularity in the parenchyma. Only a minimal inflammatory cell infiltrate was identified and was limited to the tenosynovium and/or paratenon. No differences were identified between titanium and stainless steel implants and those with a ramped design. Although all animals lost wrist motion with time, no differences were observed between groups. Our results suggest that pi plate placement on the dorsal surface of the distal radius may lead to extensor tendon irritation and dysfunction. There is no evidence to suggest that this is specifically related to titanium or plate edge design.

Animals↗

PubMed2005

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 (Brodmann's 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.

Adult↗

PubMed2005

Brain activity in cigarette smokers performing a working memory task: effect of smoking abstinence.

BACKGROUND: When nicotine-dependent human subjects abstain from cigarette smoking, they exhibit deficits in working memory. An understanding of the neural substrates of such impairments may help to understand how nicotine affects cognition. Our aim, therefore, was to identify abnormalities in the circuitry that mediates working memory in nicotine-dependent subjects after they initiate abstinence from smoking. METHODS: We used blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to study eight smokers while they performed a letter version of the N-Back working memory task under satiety (< or = 1.5 hours abstinence) and abstinence (> or = 14 hours abstinence) conditions. RESULTS: Task-related activity in the left dorsal lateral prefrontal cortex (DLPFC) showed a significant interaction between test session (satiety, abstinence) and task load (1-back, 2-back, and 3-back). This interaction reflected the fact that task-related activity in the satiety condition was relatively low during performance of the 1-back task but greater at the more difficult task levels, whereas task-related activity in the abstinence condition was relatively high at the 1-back level and did not increase at the more difficult task levels. CONCLUSIONS: We conclude that neural processing related to working memory in the left DLPFC is less efficient during acute abstinence from smoking than at smoking satiety.

Adult↗

PubMed2005

Working memory in cigarette smokers: comparison to non-smokers and effects of abstinence.

The present study was designed to examine the effect of cigarette smoking and withdrawal on working memory. Participants included 15 smokers and 22 matched non-smokers. For both groups the N-Back Task (of working memory) was administered in two test blocks on each of two days. On one day, smokers were tested after >or=13 h abstinence; on the other day, testing began or=13 h but not <or=1 h abstinence was significantly less accurate than that of non-smokers. A within-subject comparison revealed that in the abstinence session, smokers had significantly longer response latencies (in the 2-back condition) and made more overall errors compared to the satiety session. Smoking between test blocks in the abstinence session did not significantly affect performance although it significantly reduced craving. These findings provide further evidence for a deficit in working memory associated with acute abstinence from smoking, which may contribute to the difficulty of smoking cessation.

Adult↗

PubMed2005

Hippocampal activations during encoding and retrieval in a verbal working memory paradigm.

Though the hippocampus has been associated with encoding and retrieval processes in episodic memory, the precise nature of its involvement in working memory has yet to be determined. This functional magnetic resonance imaging (fMRI) study employed a verbal working memory paradigm that allows for the within-subject comparison of functional activations during encoding, maintenance, and retrieval. In each trial, participants were shown 5 target words and, after an 8 s delay, a series of probe words. Probe words consisted of target matches, phonetically or semantically related foils, or foils unrelated to the target words. Both the left and right hippocampi showed higher mean activation amplitudes during encoding than maintenance. In contrast, the right dorsolateral prefrontal cortex (DLPFC) showed greater activation during maintenance than encoding. Both hippocampal and DLPFC regions were more active during retrieval than maintenance. Furthermore, an analysis of retrieval activation separated by probe type showed a trend toward greater bilateral hippocampal activation for probes related (both semantically and phonetically) to the target than for unrelated probes and still greater activation for target matches. This pattern suggests that there may be roles for the hippocampus and DLPFC in working memory that change as function of information processing stage. Additionally, the trend towards increased involvement of the hippocampus with the increase in relatedness of the probe stimuli to the information maintained is interpreted to be consistent with the role of the hippocampus in recollection-based retrieval in long-term memory and may indicate that this role extends to working memory processes.

Adult↗

PubMed2005

Dorsolateral prefrontal cortex activity during maintenance and manipulation of information in working memory in patients with schizophrenia.

CONTEXT: It remains unclear whether altered regional brain physiological activity in patients with schizophrenia during working memory tasks relates to maintenance-related processes, manipulation-related (ie, executive) processes, or both. OBJECTIVE: To examine regional functional activations of the brain during maintenance- and manipulation-related working memory processing in patients with schizophrenia and in healthy comparison subjects. DESIGN: Functional images of the brain were acquired in 11 schizophrenic patients and 12 healthy control subjects (matched for age, sex, handedness, and parental education) during 2 spatial working memory paradigms, one contrasting maintenance-only processing with maintenance and manipulation processing and the other contrasting parametrically varying maintenance demands. RESULTS: Patients and controls showed activation of a large, spatially distributed network of cortical and subcortical regions during spatial working memory processing. When task demands required explicit manipulation of information held in memory, controls recruited right dorsolateral prefrontal cortex (Brodmann areas 45 and 46) to a significantly greater extent than patients. A similar effect was observed for the larger memory set sizes of the memory set size task. No other brain regions showed activation differences between groups for either task. These differences persisted when comparing activation maps for memory set sizes in which the 2 groups were equivalent in behavioral accuracy and when comparing subgroups of patients and controls matched for behavioral accuracy on either task. CONCLUSIONS: Physiological disturbances in the dorsolateral prefrontal cortex contribute differentially to patients' difficulties with maintaining spatial information across a brief delay, as well as with manipulating the maintained representation. These differences persisted when comparing conditions in which the 2 groups were equivalent in behavioral accuracy.

Adolescent↗

PubMed2005

Use of bone graft substitutes and bioactive materials in treatment of distal radius fractures.

Although autogenous bone graft has been shown to be useful in the treatment of distal radius fractures, the role of bone graft substitutes and the optimal replacement material remains unclear. Several products are commercially available, each with differing osteoconductive, osteoinductive, and structural properties. Indications and choice of graft substitute should be based on the needs of the individual case with regard to need for structural support, gap filling, or bone healing stimulation. Further comparative research will help clarify the indications and most appropriate material for a given fracture and clinical situation.

Biocompatible Materials↗

PubMed2005

Bilateral neurostimulation systems used for deep brain stimulation: in vitro study of MRI-related heating at 1.5 T and implications for clinical imaging of the brain.

Deep brain stimulation (DBS) is used increasingly in the field of movement disorders. The implanted electrodes create not only a prior risk to patient safety during MRI, but also a unique opportunity in the collection of functional MRI data conditioned by direct neural stimulation. We evaluated MRI-related heating for bilateral neurostimulation systems used for DBS with an emphasis on assessing clinically relevant imaging parameters. Magnetic resonance imaging was performed using transmit body radiofrequency (RF) coil and receive-only head RF coil at various specific absorption rates (SARs) of RF power. In vitro testing was performed using a gel-filled phantom with temperatures recorded at the electrode tips. Each DBS electrode was positioned with a single extension loop around each pulse generator and a single loop at the "head" end of the phantom. Various pulse sequences were used for MRI including fast spin-echo, echo-planar imaging, magnetization transfer contrast and gradient-echo techniques. The MRI sequences had calculated whole-body averaged SARs and local head SARs ranging from 0.1 to 1.6 W/kg and 0.1 to 3.2 W/kg, respectively. Temperature elevations of less than 1.0 degrees C were found with the fast spin-echo, magnetization transfer contrast, gradient-echo and echo-planar clinical imaging sequences. Using the highest SAR levels, whole-body averaged, 1.6 W/kg, local exposed-body, 3.2 W/kg, and local head, 2.9 W/kg, the temperature increase was 2.1 degrees C. These results showed that temperature elevations associated with clinical sequences were within an acceptable physiologically safe range for the MR conditions used in this evaluation, especially for the use of relatively low SAR levels. Notably, these findings are highly specific to the neurostimulation systems, device positioning technique, MR system and imaging conditions used in this investigation.

Deep Brain Stimulation↗

PubMed2005

Outpatient minimally invasive parathyroidectomy using local/regional anesthesia: a safe and effective operative approach for selected patients.

BACKGROUND: Minimally invasive parathyroidectomy (MIP) using local/regional anesthesia has become an accepted treatment for selected patients with primary hyperparathyroidism (HPT) and can be performed in the ambulatory setting. METHODS: From 1999 to 2004, 139 consecutive patients at our institution with HPT caused by a single localized parathyroid adenoma underwent MIP through a 2.5- to 3-cm incision. Anesthesia included preoperative local/regional blocks with moderate intravenous sedation. Patient follow-up data were reviewed retrospectively. RESULTS: All 139 MIP patients had biochemical HPT and a single adenoma localized by sestamibi scan alone (n = 119; 86%) or combined with other imaging (n = 20; 14%). The mean adenoma size was 1,184 +/- 1,091 mg. Total calcium and parathyroid hormone levels were 11.3 +/- 0.8 mg/dL and 451 pg/mL preoperatively, respectively, decreasing to 9.4 +/- 0.6 mg/dL and 34 pg/mL postoperatively, respectively. Of MIP cases, 117 (84%) were completed with local/regional anesthesia, and 22 (16%) used general anesthesia (4 local/regional conversions). The mean operative time when reported was 56 +/- 21 minutes (n = 28). Same-day discharges occurred for 120 (86%) patients, whereas 16 patients were observed overnight and 3 patients were observed for 48 hours. Operative cure was achieved in 137 (98.6%) patients (follow-up period, 15.2 +/- 12.4 mo) with 1 morbidity (0.7%). CONCLUSIONS: Outpatient MIP is safe and effective in selected patients. A low morbidity (0.7% in this series), rapid recovery, and high biochemical cure rate (98.6%) parallels 4-gland exploration under general anesthesia.

Adenoma↗

PubMed2005

Long-term functionality of cryopreserved parathyroid autografts: a 13-year prospective analysis.

BACKGROUND: The functional results of cryopreserved heterotopic parathyroid autotransplantation (CHPA) are not well defined. The authors evaluated the outcomes of delayed CHPA for the treatment of surgically induced hypoparathyroidism. METHODS: Since November 1991, 448 parathyroid samples from 436 patients were cryopreserved at our institution. Of these, 29 patients underwent 34 CHPA procedures, with placement of 20 to 25 pieces of parathyroid tissue (approximately 50 to 75 mg) into the forearm. Outcomes were determined based on peripheral parathyroid hormone (PTH) levels and, where available, PTH gradients between grafted and nongrafted arms. Graft function results were defined as completely functional (patients with normal PTH and calcium levels off all calcium/vitamin D supplementation), partially functional (normal PTH levels and mild hypocalcemia on calcium supplementation), or nonfunctional (low PTH levels and dependent on calcium/vitamin D supplementation). RESULTS: Of the 29 patients with CHPA, prospective data were available for 26 patients undergoing 30 CHPA procedures (9 patients with MEN 1, 4 with MEN 2A, 1 with MEN 2B, and 12 with sporadic hyperparathyroidism). The mean follow-up interval was 2 years. Twelve of 26 patients (46%) had completely functional grafts, 6 patients (23%) had partially functional grafts, and the remaining 8 patients (31%) had nonfunctional grafts. No patient with CHPA had graft-dependent recurrent hyperparathyroidism. Of the 14 patients (15 autografts) with MEN, 7 patients (50%) had fully functional grafts, and 2 patients (14%) had partially functional grafts. The mean cryopreservation period was 7.9 months (range, 1 week to 22 months) for functional autografts and 15.3 months (range, 2 weeks to 106 months) for nonfunctional autografts (P < .01). CONCLUSIONS: Based on these data and those in previous studies, approximately 60% of delayed, cryopreserved parathyroid autografts are functional. In this study 40% autografts (46% of patients) achieved full competency off supplements. Some patients have evidence of graft function with normal PTH levels but are not normocalcemic. Results were similar for patients with MEN and nonhereditary hyperparathyroidism. The duration of cryopreservation was a significant indicator of graft failure, and no functional autograft was observed beyond 22 months of preservation. CHPA is a useful treatment modality for patients with postoperative hypocalcemia after thyroid or parathyroid surgery, who do not respond to immediate parathyroid autotransplantation.

Adolescent↗

PubMed2005

Regional brain activity associated with visual backward masking.

In visual backward masking, the visibility of a briefly presented visual target is disrupted by a mask that is presented shortly thereafter. The goal of the current study was to identify regions in the human cortex that may provide the neural basis of visual masking. We searched for areas whose activity correlated with perception as we systematically varied the strength of masking. A total of 13 subjects performed a backward masking task during functional magnetic resonance imaging. Target and mask were presented at three delay intervals (34, 68, and 102 msec) and behavioral measures confirmed that the targets were more visible at longer masking intervals. Two sets of regions of interest were identified: Distinct regions in the visual cortex (V1/V2, LO, hMT+) were segregated using scans to localize visual processing drawn from the existing literature. Additional cortical regions were selected in a data-driven approach based on their activity during the backward masking task. For each set, we determined the regions whose magnitude of activation increased at longer masking intervals. Nine of the subjects provided valid behavioral performance data on the visual masking task and imaging data from these subjects were used for subsequent analysis. The scans of visual processing areas identified four regions, including: early visual areas (V1 and V2), the motion-sensitive regions in the lateral occipital (LO) lobe (hMT+), and two components (dorsal and ventral) of the object-sensitive region, LO. Of these, the ventral and dorsal LO regions were sensitive to the strength of the mask. For the data-driven approach, six regions were identified on the basis of a difference map in which all masking intervals were contrasted with rest. These included the inferior parietal, anterior cingulate, precentral, insula, thalamic, and occipital areas. The predicted effects of more activity with weaker masking were seen in the thalamus, inferior parietal, and anterior cingulate. This study isolated three types of visual processing areas. The first included regions that subserve key stages of vision (including object and motion processing). The second type responded to the presentation of brief ly presented visual stimuli, regardless of masking interval. The third type (selected from the first two) included regions sensitive to the interval between the target and mask. These latter regions (including ventral LO, inferior parietal, anterior cingulate, and thalamus) may form the neural substrate of backward masking.

Adult↗

PubMed2005

Increased amygdala activation during mania: a functional magnetic resonance imaging study.

OBJECTIVE: This study sought to investigate neural activity in the amygdala during episodes of mania. METHOD: Nine manic subjects and nine healthy comparison subjects underwent functional magnetic resonance imaging (fMRI) while performing a neuropsychological paradigm known to activate the amygdala. Subjects viewed faces displaying affect (experimental task) and geometric forms (control task) and matched them to one of two simultaneously presented similar images. RESULTS: Manic subjects had significantly increased activation in the left amygdala and reduced bilateral activation in the lateral orbitofrontal cortex relative to the comparison subjects. CONCLUSIONS: Increased activation in the amygdala and decreased activation in the orbitofrontal cortex may represent disruption of a specific neuroanatomic circuit involved in mania. These brain regions may be implicated in disorders involving regulation of affect.

Adult↗