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Biomedical subjects

Emad N Eskandar

Publications and source records attributed to Emad N Eskandar.

16 recordsLinked to original sources
PubMed2006

Selective enhancement of associative learning by microstimulation of the anterior caudate.

Primates have the remarkable ability to rapidly adjust or modify associations between visual cues and specific motor responses. Whereas little is known as to how such adjustments in behavioral policy are implemented, recent learning models suggest that the anterior striatum is optimally positioned to have a role in this process. We recorded from single units and delivered microstimulation in the striatum of rhesus monkeys performing an associative learning task. Caudate activity during reinforcement was closely correlated with the rate of learning and peaked during the steepest portion of the learning curve when new associations were being acquired. Moreover, delivering microstimulation in the caudate during the reinforcement period significantly increased the rate of learning without altering the monkeys' ultimate performance. These findings suggest that the caudate is responsible for implementing selective adjustments to the 'associative weights' between sensory cues and motor responses during learning, thus enhancing the likelihood of selecting profitable actions.

Animals↗
PubMed2006

Multimodality treatment of trigeminal neuralgia.

Most trigeminal neuralgia (TN) studies focus on a single strategy, microvascular decompression (MVD) or percutaneous rhizotomy (PR). We use a multimodality approach to TN. We perform MVD on patients younger than 70 years and PR on older patients or those where MVD has failed. We performed a chart review of the procedures for TN over the past 3 years and used a questionnaire for long-term follow-up. The questionnaire asked patients to rate their pre- and postoperative pain, outcome, and medication changes. Seventy-four procedures (40 MVDs and 34 PRs) were performed on 67 patients. Twenty patients had undergone previous procedures. 93% of the patients had significant initial pain relief. Over a 1.2-year mean follow-up, 51% of the patients had complete pain relief while 27% had a substantial improvement. There were no deaths and 5 complications. Our results suggest that a multimodality approach to TN yields excellent results with minimal complications.

Age Factors↗
PubMed2006

Efficacy of surgical treatment of de novo, adult-onset, cryptogenic, refractory focal status epilepticus.

BACKGROUND: There have been few published reports of successful surgical treatment of focal status epilepticus. Surgical intervention is considered a last resort after medical strategies have been exhausted. OBJECTIVE: To report a case of an adult who was initially seen with de novo, medically refractory, cryptogenic focal status epilepticus and underwent resection of an electrographically defined portion of the left middle frontal gyrus with multiple subpial transections of the adjacent cortex resulting in termination of the electroclinical seizure activity. DESIGN: Report of a case of successful surgical treatment of cryptogenic focal status epilepticus. INTERVENTION: After an initial 35 days of oral antiepileptic drug therapy and subsequent 16 days of continuous electroencephalography-guided intravenous antiepileptic drug therapy in an intensive care unit setting, and after extensive preoperative and intraoperative characterization of the epileptogenic zone, a tailored resection of the left middle frontal gyrus with multiple subpial transections of the surrounding cortex was performed. RESULTS: The restricted surgical resection and multiple subpial transections terminated the seizure activity. Neuropathological examination of the resected tissue revealed moderate inflammatory changes and a few abnormally located neurons without any definitive evidence of dysplasia, which was suspected preoperatively. CONCLUSIONS: We suggest that focal cortical resection may be an appropriate intervention in medically refractory focal status epilepticus even when an overt structural etiology is not evident preoperatively and should be considered as an option at the onset of intractability.

Adult↗
PubMed2006

Experience with microelectrode guided subthalamic nucleus deep brain stimulation.

OBJECTIVE: Subthalamic deep brain stimulation (DBS) has rapidly become the standard surgical therapy for medically refractory Parkinson disease. However, in spite of its wide acceptance, there is considerable variability in the technical approach. This study details our technique and experience in performing microelectrode recording (MER) guided subthalamic nucleus (STN) DBS in the treatment of Parkinson disease. METHODS: Forty patients underwent surgery for the implantation of 70 STN DBS electrodes. Stereotactic localization was performed using a combination of magnetic resonance and computed tomographic imaging. We used an array of three microelectrodes, separated by 2 mm, for physiological localization of the STN. The final location was selected based on MER and macrostimulation through the DBS electrode. RESULTS: The trajectory selected for the DBS electrode had an average pass through the STN of 5.6 +/- 0.4 mm on the left and 5.7 +/- 0.4 mm on the right. The predicted location was used in 42% of the cases but was modified by MER in the remaining 58%. Patients were typically discharged on the second postoperative day. Eighty-five percent of patients were sent home, 13% required short-term rehabilitation, and one patient required long-term nursing services. Seven complications occurred over 4 years. Four patients suffered small hemorrhages, one patient experienced a lead migration, one developed an infection of the pulse generator, and one patient suffered from a superficial cranial infection. CONCLUSION: Simultaneous bilateral MER-guided subthalamic DBS is a relatively safe and well-tolerated procedure. MER plays an important role in optimal localization of the DBS electrodes.

Aged↗
PubMed2005

Timing and direction selectivity of subthalamic and pallidal neurons in patients with Parkinson disease.

Current models of basal ganglia function suggest that some manifestations of Parkinson disease (PD) arise from abnormal activity and decreased selectivity of neurons in the subthalamic nucleus (STN) and globus pallidus internus (Gpi). Our goal was to examine the timing and direction selectivity of neuronal activity relative to visually guided movements in the STN and Gpi of patients with PD. Recordings were made from 152 neurons in the STN and 33 neurons in the Gpi of awake subjects undergoing surgery for PD. Corresponding EMG data were obtained for half the cells. We employed a structured behavioral task in which the subjects used a joystick to guide a cursor to one of four targets displayed on a monitor. Each direction was tested over multiple trials. Movement-related modulation of STN activity began on average 264+/-10 ms before movement initiation and 92+/-13 ms before initial EMG activity, while modulation of Gpi activity began 204+/-21 ms before overt movement initiation. In the STN, 40% of cells demonstrated perimovement activity, and of these 64% were directionally selective. In Gpi, 45% of cells showed perimovement activity of which 80% were selective. In both nuclei, directionally selective cells had significantly lower baseline firing rates than nonselective cells (41+/-5 vs 59+/-4 spikes/s in STN, and 50+/-9 vs 74+/-15 spikes/s in Gpi). These results suggest that STN activity occurs earlier than previously reported, and that higher neuronal firing rates maybe associated with decreased direction selectivity in PD patients.

Action Potentials↗
PubMed2005

Spinal epidural abscess: clinical presentation, management, and outcome.

BACKGROUND: We sought to describe the clinical characteristics of patients with spinal epidural abscess and to relate presentation and treatment to short-term clinical and neurologic outcome. METHODS: We retrospectively reviewed the records and radiographic images of all patients admitted to our institution with a diagnosis of spinal epidural abscess between January 1995 and March 2001. RESULTS: Thirty males and 18 females were admitted with spinal epidural abscess. Median age was 61 years (range, 31-84). Twenty-three of 48 patients were febrile at presentation and the mean white blood cell (WBC) count was 15.5 (range, 4.0-38.7). Twenty-seven patients presented with motor deficits, 17 with pain alone, 2 with sepsis, 1 with dysphagia, and 1 incidentally on spinal imaging. Intravenous drug abuse was the most common risk factor (13 patients) followed by the presence of nonspinal infection, including endocarditis (10 patients). Blood cultures were positive in 29 patients. Staphylococcus aureus was the most common organism cultured from abscesses. Collections were located in the cervical spine in 11 patients, cervicothoracic in 4, thoracic in 7, thoracolumbar in 4, and lumbosacral in 22. One patient harbored both cervical and lumbar epidural abscesses. Twenty-three patients initially received nonoperative therapy with antibiotics alone; 25 underwent urgent surgery. Eleven patients initially treated with antibiotics eventually deteriorated and required delayed surgery. Patients receiving antibiotics suffered a significantly greater number of unfavorable outcomes (clinical deterioration or death) than those in the early surgical group (P < 0.005). CONCLUSIONS: Patients with spinal epidural abscess may be normothermic and have normal WBC counts. Urgent surgery was more likely to be offered to patients presenting with neurologic deficits than with pain alone. Patients treated without early surgery were significantly more likely to deteriorate and suffer poor outcomes.

Adult↗
PubMed2005

Deep brain stimulation of the anterior internal capsule for the treatment of Tourette syndrome: technical case report.

OBJECTIVE AND IMPORTANCE: Medical treatment of Tourette syndrome is often ineffective or is accompanied by debilitating side effects, therefore prompting the need to evaluate surgical therapies. CLINICAL PRESENTATION: We present the case of a 37-year-old woman with severe Tourette syndrome since the age of 10 years. Her symptoms included frequent vocalizations and severe head and arm jerks that resulted in unilateral blindness. Trials of more than 40 medications and other therapies had failed to relieve the tics. INTERVENTION: We implanted bilateral electrodes in the anterior limb of the internal capsule, terminating in the vicinity of the nucleus accumbens. At 18-month follow-up, optimal stimulation continued to lower her tic frequency and severity significantly. CONCLUSION: Our findings suggest that stimulation of the anterior internal capsule may be a safe and effective procedure for the treatment of Tourette syndrome.

Adult↗
PubMed2004

Visually guided movements suppress subthalamic oscillations in Parkinson's disease patients.

There is considerable evidence that abnormal oscillatory activity in the basal ganglia contributes to the pathogenesis of Parkinson's disease. However, little is known regarding the relationship of oscillations to volitional movements. Our goal was to evaluate the dynamics of oscillatory activity at rest and during movement. We performed microelectrode recordings from the subthalamic nucleus (STN) of patients undergoing deep brain stimulation surgery. During recordings, the patients used a joystick to guide a cursor to one of four targets on a monitor. We recorded 184 cells and 47 pairs of cells in 11 patients. At rest, 26 cells (14%) demonstrated significant oscillatory activity, with a mean frequency of 18 Hz. During movement, this oscillatory activity was either reduced or completely abolished in all of the cells. At rest, 18 pairs (38%) of cells in five patients exhibited synchronized oscillatory activity, with a mean frequency of 15 Hz. In 17 of the 18 pairs, both of the cells exhibited oscillations, and, in one pair, only one of the cells was oscillatory. These synchronized oscillations were also significantly decreased with movement. There was a strong inverse correlation between firing rates and oscillatory activity. As the firing rates increased with movement, there was a decrease in oscillatory activity. These findings suggest that visually guided movements are associated with a dampening and desynchronization of oscillatory activity in STN neurons. One possible explanation for these observations is that the increased cortical drive associated with movement preparation and execution leads to a transient dampening of STN oscillations, hence facilitating movement.

Action Potentials↗
PubMed2004

Human anterior cingulate neurons and the integration of monetary reward with motor responses.

The human dorsal anterior cingulate cortex (dACC) has been implicated in cognitive processes that have been proposed to play a role in integrating contextual information needed to select or modify appropriate motor responses. In humans, however, there has been little direct evidence tying the dACC to the integration of contextual information and behavioral response. We used single-neuron recordings from human subjects to evaluate the role of the dACC in reward-based decision making. Subjects undergoing planned surgical cingulotomy performed a task where they were instructed to make specific movements in response to changing monetary rewards. In many neurons, activity increased in response to a diminished reward, and was also predictive of the movement ultimately made. After dACC ablation, subjects made selectively more errors when they were required to change movement based on reward reduction. These findings suggest that the dACC in humans plays an important role in linking reward-related information with alternative actions.

Analysis of Variance↗
PubMed2003

Parietal activity and the perceived direction of ambiguous apparent motion.

We recorded from parietal neurons in monkeys (Macacca mulatta) trained to report the direction of an apparent motion stimulus consisting of regularly spaced columns of dots surrounded by an aperture. Displacing the dots by half their inter-column spacing produced vivid apparent motion that could be perceived in either the preferred or anti-preferred direction for each neuron. Many neurons in the lateral intraparietal area (LIP) responded more strongly on trials in which the animals reported perceiving the neurons' preferred direction, independent of the hand movement used to report their percept. This selectivity was less common in the medial superior temporal area (MST) and virtually absent in the middle temporal area (MT). Variations in activity of LIP and MST neurons just before motion onset were also predictive of the animals' subsequent perceived direction. These data suggest a hierarchy of representation in parietal cortex, whereby neuronal responses become more aligned with subjective perception in higher parietal areas.

Action Potentials↗
PubMed2003

Microvascular decompression surgery in the United States, 1996 to 2000: mortality rates, morbidity rates, and the effects of hospital and surgeon volumes.

OBJECTIVE: Microvascular decompression (MVD) is associated with low mortality and morbidity rates at specialized centers, but many MVD procedures are performed outside such centers. We studied short-term end points after MVD in a national hospital discharge database sample. METHODS: A retrospective cohort study was performed by using the Nationwide Inpatient Sample, 1996 to 2000. RESULTS: The sample included 1326 MVD procedures for treatment of trigeminal neuralgia, 237 for treatment of hemifacial spasm, and 27 for treatment of glossopharyngeal neuralgia, performed at 305 hospitals by 277 identified surgeons. The mortality rate was 0.3%, and the rate of discharge other than to home was 3.8%. Neurological complications were coded in 1.7% of cases, hematomas in 0.5%, and facial palsies in 0.6%, with 0.4% of patients requiring ventriculostomies and 0.7% postoperative ventilation. Trigeminal nerve section was also coded for 3.4% of patients with trigeminal neuralgia, more commonly among older patients (P = 0.08), among female patients (P = 0.03), and at teaching hospitals (P = 0.02). The median annual caseloads were 5 cases per hospital (range, 1-195 cases) and 3 cases per surgeon (range, 1-107 cases). With adjustment for age, sex, race, primary insurance, diagnosis (trigeminal neuralgia versus hemifacial spasm versus glossopharyngeal neuralgia), geographic region, admission type and source, and medical comorbidities, outcomes at discharge were superior at higher-volume hospitals (P = 0.006) and with higher-volume surgeons (P = 0.02). Complications were less frequent after surgery performed at high-volume hospitals (P = 0.04) or by high-volume surgeons (P = 0.01). The rate of discharge other than to home was 5.1% for the lowest-volume-quartile hospitals, compared with 1.6% for the highest-volume-quartile hospitals. Volume and mortality rate were not significantly related, but three of the four deaths in the series followed procedures performed by surgeons who had performed only one MVD procedure that year. Length of stay (median, 3 d) and hospital volume were not significantly related. Hospital charges were slightly higher at higher-volume hospitals (P = 0.007). CONCLUSION: Although most MVD procedures in the United States are performed at low-volume centers, mortality rates remain low. Morbidity rates are significantly lower at high-volume hospitals and with high-volume surgeons.

Adolescent↗
PubMed2003

Surgery for Parkinson disease in the United States, 1996 to 2000: practice patterns, short-term outcomes, and hospital charges in a nationwide sample.

OBJECT: The surgical treatment of Parkinson disease (PD) has undergone a dramatic shift, from stereotactic ablative procedures toward deep brain stimulaion (DBS). The authors studied this process by investigating practice patterns, mortality and morbidity rates, and hospital charges as reflected in the records of a representative sample of US hospitals between 1996 and 2000. METHODS: The authors conducted a retrospective cohort study by using the Nationwide Inpatient Sample database; 1761 operations at 71 hospitals were studied. Projected to the US population, there were 1650 inpatient procedures performed for PD per year (pallidotomies, thalamotomies, and DBS), with no significant change in the annual number of procedures during the study period. The in-hospital mortality rate was 0.2%, discharge other than to home was 8.1%, and the rate of neurological complications was 1.8%, with no significant differences between procedures. In multivariate analyses, hospitals with larger annual caseloads had lower mortality rates (p = 0.002) and better outcomes at hospital discharge (p = 0.007). Placement of deep brain stimulators comprised 0% of operations in 1996 and 88% in 2000. Factors predicting placement of these devices in analyses adjusted for year of surgery included younger age, Caucasian race, private insurance, residence in higher-income areas, hospital teaching status, and smaller annual hospital caseload. In multivariate analysis, total hospital charges were 2.2 times higher for DBS (median dollar 36,000 compared with dollar 12,000, p < 0.001), whereas charges were lower at higher-volume hospitals (p < 0.001). CONCLUSIONS: Surgical treatment of PD in the US changed significantly between 1996 and 2000. Larger-volume hospitals had superior short-term outcomes and lower charges. Future studies should address long-term functional end points, cost/benefit comparisons, and inequities in access to care.

Adult↗
PubMed2002

Distinct nature of directional signals among parietal cortical areas during visual guidance.

We examined neuronal signals in the monkey medial superior temporal area (MST), the medial intraparietal area (MIP), and the lateral intraparietal area (LIP) during visually guided hand movements. Two animals were trained to use a joystick to guide a spot to a target. Many neurons responded in a direction-selective manner in this guidance task. We tested whether the direction selectivity depended on the direction of the stimulus spot or the direction of the hand movement. First, in some trials, the moving spot disappeared transiently. Second, the mapping between the hand direction and the spot direction was reversed on alternate blocks of trials. Third, we recorded the spot's movement while the animals moved the joystick and then played back that movement while the animals fixated without moving the joystick. Neurons in the three parietal areas conveyed distinct directional information. MST neurons were active and directional only on visible trials in both joystick-movement mode and playback mode and were not affected by the direction of hand movement. MIP neurons were mainly directional with respect to the hand movement, although some MIP neurons were also selective for stimulus direction. MIP neurons were much less active in playback mode. LIP neurons were active and directional in both joystick-movement mode and playback mode. Directional signals in LIP were unrelated to planning saccades. The selectivity of LIP neurons also became evident hundreds of milliseconds before the start of movement. Since the direction of movement was consistent throughout a block of trials, these signals could provide a prediction of the upcoming direction of motion. We tested this by alternating blocks of trials in which the direction was consistent or randomized. The direction selectivity developed earlier on trials in which the upcoming direction could be predicted. These results suggest that LIP neurons combine "bottom-up" visual motion signals with extraretinal, predictive signals about stimulus motion.

Animals↗
PubMed2002

Spinal dural arteriovenous fistulas: experience with endovascular and surgical therapy.

OBJECT: Although the pathophysiology of spinal dural arteriovenous fistulas (AVFs) has recently been elucidated, the optimal treatment strategy for these lesions has yet to be defined. Current management techniques include endovascular embolization or microsurgical obliteration. METHODS: The authors reviewed the records and angiograms of all patients with spinal dural AVFs treated at Massachusetts General Hospital over a 6-year period (1992-1998). During this period, it was intended initially to treat all patients with embolization and to reserve surgery for those in whom endovascular treatment failed or in cases in which pretreatment evaluation suggested that endovascular therapy would be ineffective or unsafe. A total of 26 patients with spinal dural AVFs were treated: there were 22 men and 4 women with a mean age of 65 years (range 39-79 years). Lesions were located in the following areas: five in foramen magnum/cervical, 13 in thoracic, five in lumbar, and three in sacral. Twenty-three (88%) of 26 patients underwent embolization and three (12%) of 23 patients underwent surgery as the primary mode of treatment. Of the 23 patients in whom embolization was performed or attempted, nine (39%) ultimately required surgery. All patients were stabilized or improved following definitive treatment, as assessed by the Aminoff-Logue scores. There was one death secondary to a myocardial infarction. CONCLUSIONS: These data demonstrate that endovascular therapy can be successful as an initial treatment for the majority of patients; however, there is a 39% failure rate, which is not observed following surgical therapy. Once a definitive therapy has been achieved using either technique virtually all patients are either stabilized or improved.

Adult↗