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Joseph R Madsen

Publications and source records attributed to Joseph R Madsen.

18 recordsLinked to original sources
PubMed2006

Hippocampal and neocortical gamma oscillations predict memory formation in humans.

Functional magnetic resonance imaging (fMRI) of the human brain has shown that the hippocampus and the left temporal and frontal cortices play a key role in the formation of new verbal memories. We recorded electrical activity from 2349 surgically implanted intracranial electrodes in epilepsy patients while they studied and later recalled lists of common words. Using these recordings, we demonstrate that gamma oscillations (44-64 Hz) in the hippocampus and the left temporal and frontal cortices predict successful encoding of new verbal memories. This increase in gamma oscillations was not seen in other frequency bands, whose activity generally decreased during successful memory formation. These findings identify a role for gamma oscillations in verbal memory formation with the hippocampus and the left temporal and frontal cortices, the same regions implicated using noninvasive fMRI recording methods.

Adaptation, Physiological↗
PubMed2006

Electroencephalography in epilepsy surgery planning.

OBJECTIVE: To describe localizing value of surface EEG recording in the presurgical evaluation of medically intractable pediatric epilepsy patients. METHODS: We review the relevant concepts required for understanding the role of surface EEG in the presurgical evaluation and in identifying the epileptogenic zone. The unique features of EEG and its limitations are discussed. CONCLUSION: Despite recent technological advancements, surface EEG continues to play a crucial role in defining the epileptogenic zone, and thus in presurgical planning.

Child, Preschool↗
PubMed2006

Human neocortical oscillations exhibit theta phase differences between encoding and retrieval.

We analyzed intracranial brain activity recorded from human participants during the performance of a working-memory task. We show that 6-13 Hz activity exhibits consistent phase across trials following experimental stimuli, and that this phase significantly differs between study and test stimuli. These findings suggest that oscillatory phase reflects the encoding-retrieval state of neural networks, supporting predictions of recent models of memory.[Hasselmo, M.E., Wyble, B.P., and Bodelon, C., 2002. A proposed function for hippocampal theta rhythm: Separate phases of encoding and retrieval enhance reversal of prior learning. Neural Comput. 14 793-817.; Judge, S.J., Hasselmo, M.E., 2004. Theta rhythmic stimulation of stratum lacunosum-moleculare in rat hippocampus contributes to associative LTP at a phase offset in stratum radiatum. J. Neurophys. 92 1516-1624.].

Adolescent↗
PubMed2006

What we don't (but should) know about hydrocephalus.

In an effort to identify critical gaps in the prevailing knowledge of hydrocephalus, the authors formulated 10 key questions. 1) How do we define hydrocephalus? 2) How is cerebrosinal fluid (CSF) absorbed normally and what are the causes of CSF malabsorption in hydrocephalus? 3) Why do the ventricles dilate in communicating hydrocephalus? 4) What happens to the structure and function of the brain when it is compressed and stretched by the expanding ventricles? 5) What is the role of cerebrovenous pressure in hydrocephalus? 6) What causes normal-pressure hydrocephalus? 7) What causes low-pressure hydrocephalus? 8) What is the pathophysiology of slit ventricle syndrome? 9) What is the pathophysiological basis for neurological impairment in hydrocephalus, and to what extent is it reversible? 10) How is the brain of a child with hydrocephalus different from that of a young or elderly adult? Rigorous answers to these questions should lead to more effective and reliable treatments for this disorder.

Adolescent↗
PubMed2004

Gamma EEG dynamics in neocortex and hippocampus during human wakefulness and sleep.

Little is known about the neurophysiological mechanisms underlying the human sleep-wake cycle. Using intracranial electrodes in humans, we investigated changes in topographic distribution of gamma power and local- and long-range gamma EEG coherence in neocortex and hippocampus during different cerebral states. We report significantly greater variability in gamma power across cortical regions during wakefulness than during either slow wave or rapid eye movement (REM) sleep. In addition, local (within cortical regions) and long-range (between cortical regions) gamma coherence was significantly higher during wakefulness than during sleep, and functional gamma-range coupling between the neocortex and hippocampus was seen during wakefulness, but not during sleep. These findings demonstrate a functional link between different stages of conscious awareness and the level of coupling of gamma-band oscillations in the human brain.

Adolescent↗
PubMed2004

Hip status in cerebral palsy after one year of continuous intrathecal baclofen infusion.

The purpose of this study was to assess whether reduction of muscle tone by continuous intrathecal baclofen infusion affects the progression of hip subluxation in persons with cerebral palsy. This prospective, open-label, case series was conducted at multiple specialty referral centers. There were 33 subjects, ages 4 to 31 years. All had a pretreatment lower extremity Ashworth score of >/=3; all subjects had a significant reduction in tone after a bolus injection of intrathecal baclofen and received an implanted pump for continuous delivery of intrathecal baclofen. Subjects had hip x-rays before and 1 year after pump implantation. The primary outcome measure was change in absolute hip migration percentage. One third of the hips had an increase of absolute migration percentage of 5% or more; 12% of the hips had a decrease of migration percentage of 5% or more. Change of migration percentage class was used as a second outcome criterion. 90.9% of hips manifested no deterioration or had improvement of their migration percentage class during the year of intrathecal baclofen therapy. The observed changes were not associated with the subject's age or the severity of cerebral palsy.

Adolescent↗
PubMed2004

Cerebral pathophysiology and critical care neurology: basic hemodynamic principles, cerebral perfusion, and intracranial pressure.

Pediatric neurologic intensive care differs from standard pediatric intensive care in two important respects. First, the diagnosis, monitoring, and management of problems related to disorders of cerebral perfusion and intracranial pressure (ICP) are central to nearly all of pediatric neurologic and neurosurgical intensive care. Second, various clinical problems normally encountered in the intensive care unit (ICU) have additional implications when associated with neurologic disease. Regardless of the cause, treatment should be undertaken as expeditiously as possible and should be based on the principles of resuscitation, reducing the volume of the intracranial contents, and reassessment. This chapter aims to outline some basic principles underlying the diagnosis and management of elevated ICP in children.

Brain↗
PubMed2004

Neurosurgical aspects of critical care neurology.

The management of the pediatric neurosurgical patient requires a detailed understanding of the diagnosis and management of disorders of ICP. Frequently the care of these patients will require collaboration between several different teams of physicians. Most important, frequent and clear communication between the ICU physician and the neurosurgeon will facilitate the delivery of the best-quality care to these children. This chapter will identify and discuss issues relevant to neurosurgeons and intensive care physicians taking care of children with complex problems related increased intracranial pressure.

Brain Diseases↗
PubMed2004

Antenatal neurosurgical counseling: approach to the unborn patient.

The detection and diagnosis of structural anomalies of the fetal central nervous system has become commonplace. Therefore, the pediatric neurosurgeon who will eventually care for a child postnatally can be called upon to interpret the meaning of diagnostic studies and advise the prospective parents prenatally. This article discusses some principals of prenatal counseling as they relate to neurosurgical conditions, reviews the diagnostic armamentarium for defining neurosurgical fetal conditions, and describes the common antenatal diagnoses that may be encountered by the neurosurgeon.

Brain Diseases↗
PubMed2004

Long-term outcome in children with moyamoya syndrome after cranial revascularization by pial synangiosis.

OBJECT: Moyamoya syndrome, a narrowing of the basal intracranial vessels accompanied by the development of a cloud of collateral "moyamoya" vasculature, causes cerebral ischemia and stroke. This study was undertaken to determine if a standardized neurosurgical revascularization procedure, pial synangiosis, conferred long-term benefit in pediatric patients. METHODS: The authors reviewed the clinical and radiographic records obtained in a consecutive series of patients with moyamoya syndrome. Patients were 21 years of age or younger and underwent surgery performed by a single neurosurgeon during a 17-year period. There were 143 patients (89 females and 54 males). Sixteen patients were Asian. Neurofibromatosis was present in 16 patients, 13 had undergone therapeutic cranial irradiation, and Down syndrome was present in 10. In 66 there was no known predisposing condition. Stroke had occurred in 67.8% of the population and transient ischemic attacks (TIAs) in 43.4% prior to surgery. Within the first 30 days following 271 craniotomies for pial synangiosis, there were 11 episodes of stroke (7.7% per patient; 4% per surgically treated hemisphere) and three severe TIAs. Follow-up evaluation was performed in all but one patient (mean period 5.1 years). In 126 patients followed for more than 1 year, four suffered a late-onset stroke, one suffered a severe reversible TIA without magnetic resonance imaging-documented evidence of stroke, and two experienced persistent TIAs. In 46 patients followed for more than 5 years in whom the major initial presentation was stroke alone, only two late-onset strokes have occurred. Functional status at the time of surgery determined long-term functional status. CONCLUSIONS: Following pial synangiosis, the majority of pediatric patients with moyamoya syndrome stop having strokes and TIAs, and they appear to experience an excellent long-term prognosis.

Adolescent↗
PubMed2003

Theta and gamma oscillations during encoding predict subsequent recall.

Electrophysiological and hemodynamic measures of human brain activity have been shown to distinguish between episodes of encoding items that are later recalled versus those that are not recalled (Paller and Wagner, 2002). Using intracranial recordings from 793 widespread cortical and subcortical sites in 10 epileptic patients undergoing invasive monitoring, we compared oscillatory power at frequencies ranging from 2 to 64 Hz as participants studied lists of common nouns. Significant increases in oscillatory power during encoding predicted subsequent recall, with this effect predominantly in the 4-8 Hz (theta) and 28-64 Hz (gamma) frequency bands. Sites exhibiting increased theta activity during successful encoding were clustered in right temporal and frontal cortex, whereas those exhibiting increased gamma activity appeared bilaterally at widespread cortical locations. These findings implicate theta and gamma oscillatory activity, across a widespread network of cortical regions, in the formation of new episodic memories.

Adolescent↗
PubMed2003

Sleep-dependent theta oscillations in the human hippocampus and neocortex.

Hippocampal theta waves recorded during rapid eye movement (REM) sleep are thought to play a critical role in memory consolidation in lower mammals, but previous attempts to detect similar theta oscillations in the human hippocampus have been unsuccessful. Using subdural and depth recordings from epileptic patients, we now report the first evidence of state-dependent hippocampal theta waves (4-7 Hz) in humans. Unlike the continuous theta in rodents, however, these oscillations were consistently observed during REM sleep in short (approximately 1 sec) bursts and during transitions to wake in longer epochs. Theta waves were also observed in the basal temporal lobe and frontal cortex during transitions from sleep to wake and in quiet wakefulness but not in REM, and they were not coherent with hippocampal theta oscillations. The absence of functional coupling between neocortex and hippocampus during theta periods indicates that multiple theta generators exist in the human brain, and that they are dynamically regulated by brain state. Gamma oscillations were also present during REM theta bursts, but the fluctuations in gamma power were not associated with theta phase, pointing out another significant difference between rodent and human theta properties. Together, these findings suggest that the generation mechanisms of theta oscillations in humans might have evolved from tonic to phasic in hippocampus during REM sleep and extended from hippocampus to cortex, where they appear in certain wakefulness-related states.

Adolescent↗
PubMed2003

Human theta oscillations related to sensorimotor integration and spatial learning.

oscillations in the rat hippocampus have been implicated in sensorimotor integration (Bland, 1986), especially during exploratory and wayfinding behavior. We propose that human cortical activity coordinates sensory information with a motor plan to guide wayfinding behavior to known goal locations. To test this hypothesis, we analyzed invasive recordings from epileptic patients while they performed a spatially immersive, virtual taxi driver task. Consistent with this hypothesis, we found oscillations during both exploratory search and goal-seeking behavior and, in particular, during virtual movement, when sensory information and motor planning were both in flux, compared with periods of self-initiated stillness. oscillations had different topographic and spectral characteristics during searching than during goal-seeking, suggesting that different cortical networks exhibit depending on which cognitive functions are driving behavior (spatial learning during exploration vs orienting to a learned representation during goal-seeking). In contrast, oscillations in the beta band appeared to be related to simple motor planning, likely a variant of the Rolandic mu rhythm. These findings suggest that human cortical oscillations act to coordinate sensory and motor brain activity in various brain regions to facilitate exploratory learning and navigational planning.

Adolescent↗
PubMed2003

Pharyngeal dysesthesia in refractory complex partial epilepsy: new seizure or adverse effect of vagal nerve stimulation?

Sensory symptoms are commonly seen in association with focal epilepsy, but viscerosensory auras, such as pharyngeal dysesthesias, are rarely the main clinical manifestation. With the introduction of vagal nerve stimulation (VNS) for medically refractory epilepsy, viscerosensory symptoms commonly occur as an adverse effect of VNS. Voice alterations (hoarseness or tremulousness), local neck or throat pain, and cough are the most common adverse effects seen during active stimulation (on-time). Numbness of the throat, neck, or chin, as well as a tingling sensation of the neck and throat is directly related to stimulation intensity. We present a case in which recurrent pharyngeal sensations caused a diagnostic dilemma and in which monitoring the VNS artifact during video/EEG and correlating this with clinical symptoms helped determine the etiology of the recurrent sensory symptoms.

Adult↗
PubMed2003

Gamma oscillations correlate with working memory load in humans.

Functional imaging of human cortex implicates a diverse network of brain regions supporting working memory - the capacity to hold and manipulate information for short periods of time. Although we are beginning to map out the brain networks supporting working memory, little is known about its physiological basis. We analyzed intracranial recordings from two epileptic patients as they performed a working memory task. Spectral analyses revealed that, in both patients, gamma (30-60 Hz) oscillations increased approximately linearly with memory load, tracking closely with memory load over the course of the trial. This constitutes the first evidence that gamma oscillations, widely implicated in perceptual processes, support the maintenance of multiple items in working memory.

Brain Mapping↗
PubMed2002

Biochemical characterization of pediatric brain tumors by using in vivo and ex vivo magnetic resonance spectroscopy.

OBJECT: Magnetic resonance (MR) spectroscopy provides biochemical information about tumors. The authors sought to determine the relationship between in vivo and ex vivo biochemical characterization of pediatric brain tumors by using MR spectroscopy. Their hypothesis was that ex vivo MR spectroscopy provides a link between in vivo MR spectroscopy and neuropathological analysis. METHODS: In vivo proton MR spectroscopy was performed before surgery in 11 patients with neuroepithelial tumors. During resection, a total of 40 tumor biopsy samples were obtained from within the volume of interest identified on in vivo MR spectroscopy and were frozen immediately in liquid nitrogen. High-Resolution Magic Angle Spinning (HRMAS) was used to perform ex vivo MR spectroscopy in these 40 tumor biopsy samples. Neuropathological analysis was performed using the same biopsy samples, and the tumors were classified as ependymoma, choroid plexus carcinoma, pineoblastoma (one each), and pilocytic astrocytoma, medullobastoma, low-grade glioma, and glioblastoma multiforme (two each). Ex vivo HRMAS MR spectroscopy improved line widths and line shapes in the spectra, compared with in vivo MR spectroscopy. Choline (Cho) detected in vivo corresponded to three different peaks ex vivo (glycerophosphocholine, phosphocholine [PCho], and Cho). Metabolite ratios from in vivo spectra correlated with ratios from ex vivo spectra (Pearson correlation coefficient range r = 0.72-0.91; p < or = 0.01). Metabolite ratios from ex vivo spectra, such as PCho/ total creatine (tCr) and lipid/tCr, correlated with the percentage of cancerous tissue and percentage of tumor necrosis, respectively (r = 0.84; p < 0.001). CONCLUSIONS: Agreement between in vivo and ex vivo MR spectroscopy indicates that ex vivo HRMAS MR spectroscopy can improve resolution of this modality and provide a link between in vivo MR spectroscopy and neuropathological analysis.

Adolescent↗
PubMedDate not supplied

GMFM 1 year after continuous intrathecal baclofen infusion.

The purpose of this study was to assess whether there is an improvement in motor function in persons with cerebral palsy (CP) who have had a reduction of muscle tone by continuous intrathecal baclofen infusion. This was a prospective, open label, non-blinded case series without a control group, conducted at multiple centres. There were 31 subjects, aged 4-29 years. All had a pre-treatment mean lower extremity Ashworth scores of >or= 3 and a significant reduction in tone after a bolus injection of intrathecal baclofen (ITB) and received an implanted pump for continuous delivery of ITB. Motor function was assessed by the Gross Motor Function Measure (GMFM) prior to and 1 year following pump implantation. Significant improvement (p < 0.05) in mean GMFM scores was seen in subjects < 8 years (mean change 4.1) and in those from 8-18 years (mean change 3.7) and in subjects with CP Classes 2 and 5 (mean changes 6.2 and 2.9). There was a statistically significant decrease (p < 0.05) in Ashworth scores in CP classes 2-5. Subjects or their caregivers that completed a survey about perceived changes stated that motor control, positioning and endurance improved.

Adolescent↗