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D J Mikulis

Publications and source records attributed to D J Mikulis.

At least 19 recordsLinked to original sources
PubMed2000

A multimodal cortical network for the detection of changes in the sensory environment.

Sensory stimuli undergoing sudden changes draw attention and preferentially enter our awareness. We used event-related functional magnetic-resonance imaging (fMRI) to identify brain regions responsive to changes in visual, auditory and tactile stimuli. Unimodally responsive areas included visual, auditory and somatosensory association cortex. Multimodally responsive areas comprised a right-lateralized network including the temporoparietal junction, inferior frontal gyrus, insula and left cingulate and supplementary motor areas. These results reveal a distributed, multimodal network for involuntary attention to events in the sensory environment. This network contains areas thought to underlie the P300 event-related potential and closely corresponds to the set of cortical regions damaged in patients with hemineglect syndromes.

Adolescent↗
PubMed1999

Qualitative MRI findings in adults with 22q11 deletion syndrome and schizophrenia.

BACKGROUND: A genetic syndrome associated with schizophrenia, 22q11 deletion syndrome (22qDS), may represent a genetic subtype of schizophrenia (22qDS-Sz). Structural brain changes are common in schizophrenia and may involve developmental anomalies, but there are no data yet for 22qDS-Sz. The objective of this study was to assess brain structure in adults with 22qDS-Sz using magnetic resonance imaging (MRI). METHODS: Brain and arterial MRI scans of 11 adults with 22qDS-Sz (mean age = 28.4 years, SD = 6.5) were systematically assessed by a neuroradiologist for qualitative anomalies. RESULTS: A high frequency of abnormalities were found: T2 white matter bright foci (BF), 90%; developmental midline anomalies, 45%; cerebral atrophy or ventricular enlargement, 54%; mild cerebellar atrophy, 36%; skull base abnormalities, 55%; and minor vascular abnormalities, 36%. CONCLUSIONS: BF and skull base abnormalities, especially in association with neurodevelopmental midline abnormalities, may be distinguishing MRI features for a genetic subtype of schizophrenia involving a deletion on chromosome 22.

Adult↗
PubMed1999

Cortical activation during human volitional swallowing: an event-related fMRI study.

Functional magnetic resonance imaging (fMRI) provides a safe, noninvasive method for studying task-related cortical neuronal activity. Because the cerebral cortex is strongly implicated in the control of human swallowing, we sought to identify its functional neuroanatomy using fMRI. In 10 healthy volunteers, a swallow event-related paradigm was performed by injecting 5 ml water bolus into the oral cavity every 30 s. Whole brain functional magnetic susceptibility -weighted spiral imaging data were simultaneously acquired over 600 s on a 1.5-T magnetic resonance scanner, utilizing the blood oxygenation level-dependent technique, and correlation maps were generated using both >99% percentile rank and spatial extent thresholding. We observed areas of increased signal change consistently in caudal sensorimotor cortex, anterior insula, premotor cortex, frontal operculum, anterior cingulate and prefrontal cortex, anterolateral and posterior parietal cortex, and precuneus and superiomedial temporal cortex. Less consistent activations were also seen in posterior cingulate cortex and putamen and caudate nuclei. Activations were bilateral, but almost every region, particularly the premotor, insular, and frontal opercular cortices, displayed lateralization to one or the other hemisphere. Swallow-related cortical activity is multidimensional, recruiting brain areas implicated in processing motor, sensory, and attention/affective aspects of the task.

Adult↗
PubMed1999

Thalamic stimulation and functional magnetic resonance imaging: localization of cortical and subcortical activation with implanted electrodes. Technical note.

The utility of functional magnetic resonance (fMR) imaging in patients with implanted thalamic electrodes has not yet been determined. The aim of this study was to establish the safety of performing fMR imaging in patients with thalamic deep brain stimulators and to determine the value of fMR imaging in detecting cortical and subcortical activity during stimulation. Functional MR imaging was performed in three patients suffering from chronic pain and two patients with essential tremor. Two of the three patients with pain had undergone electrode implantation in the thalamic sensory ventralis caudalis (Vc) nucleus and the other had undergone electrode implantation in both the Vc and the periventricular gray (PVG) matter. Patients with tremor underwent electrode implantation in the ventralis intermedius (Vim) nucleus. Functional MR imaging was performed during stimulation by using a pulse generator connected to a transcutaneous extension lead. Clinically, Vc stimulation evoked paresthesias in the contralateral body, PVG stimulation evoked a sensation of diffuse internal body warmth, and Vim stimulation caused tremor arrest. Functional images were acquired using a 1.5-tesla MR imaging system. The Vc stimulation at intensities provoking paresthesias resulted in activation of the primary somatosensory cortex (SI). Stimulation at subthreshold intensities failed to activate the SI. Additional stimulation-coupled activation was observed in the thalamus, the secondary somatosensory cortex (SII), and the insula. In contrast, stimulation of the PVG electrode did not evoke paresthesias or activate the SI, but resulted in medial thalamic and cingulate cortex activation. Stimulation in the Vim resulted in thalamic, basal ganglia, and SI activation. An evaluation of the safety of the procedure indicated that significant current could be induced within the electrode if a faulty connecting cable (defective insulation) came in contact with the patient. Simple precautions, such as inspection of wires for fraying and prevention of their contact with the patient, enabled the procedure to be conducted safely. Clinical safety was further corroborated by performing 86 MR studies in patients in whom electrodes had been implanted with no adverse clinical effects. This is the first report of the use of fMR imaging during stimulation with implanted thalamic electrodes. The authors' findings demonstrate that fMR imaging can safely detect the activation of cortical and subcortical neuronal pathways during stimulation and that stimulation does not interfere with imaging. This approach offers great potential for understanding the mechanisms of action of deep brain stimulation and those underlying pain and tremor generation.

Chronic Disease↗
PubMed1998

Event-related fMRI of pain: entering a new era in imaging pain.

Previous imaging studies of pain used a block design of prolonged (up to 1 min) noxious stimulation that are not well tolerated and subject to temporal interactions. We describe an adaptation of event-related fMRI to study pain with short duration stimuli. Functional images were acquired with a spiral sequence on a 1.5T GE echospeed MRI system of the thalamus, anterior cingulate, insula and second somatosensory cortex during brief (1-3 s) noxious thermal stimulation of the hand of normal volunteers. An MRI-compatible computerized rating system continuously monitored subjects' pain. Brief pain-related activations were clearly identified in the cortex and thalamus with a hemodynamic delay of 3-6 s. These findings demonstrate that brief stimuli combined with on-line pain ratings can be used to study pain with fMRI.

Acoustic Stimulation↗
PubMed1998

Cerebral gray matter volume deficits in first episode psychosis.

BACKGROUND: Structural brain differences including decreased gray matter and increased cerebrospinal fluid volumes have been observed in the brains of chronically ill patients with schizophrenia. We hypothesized that deficits in gray matter volume would be present in patients presenting with a first episode of nonaffective psychosis. METHODS: We used magnetic resonance imaging to compare the brains of 77 patients assessed as having a first episode of psychosis (meeting DSM-III-R criteria for schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, or psychotic disorder not otherwise specified) with those of 61 healthy controls matched for age, sex, race, and parental socioeconomic status. Axial, dual-echo scans of the whole brain were segmented into gray matter, white matter, and cerebrospinal fluid compartments using a computerized volumetric approach. These measures were corrected for the significant effects of intracranial volume and age prior to performing between-group comparisons. RESULTS: The first episode psychosis group had significantly smaller gray matter volume (t[136] = -2.2; P = .03) and greater cerebrospinal fluid volume (t[136] = 2.5; P = .02) than normal controls. In the patient group, gray matter volumes were positively correlated with estimates of IQ but not with age of onset, duration of illness, or measures of premorbid functioning. CONCLUSIONS: Deficits in gray matter volume are present in patients experiencing first episode nonaffective psychosis. The magnitude of these differences is smaller than has been described in more chronically ill patients.

Adolescent↗
PubMed1998

Regionalized sensorimotor plasticity after hemispherectomy fMRI evaluation.

This study demonstrates the transfer of both motor and sensory functions from one hemisphere to the other in children who had an entire cortical hemisphere surgically removed. The areas of the cortex responsible for these new functions in the remaining hemisphere are associative motor and sensory areas and do not include the typical primary motor and somatosensory regions, thus suggesting the regionalization of brain plasticity. This regionalization can be evaluated with functional magnetic resonance imaging, supporting this technique as an effective tool in the study of brain plasticity.

Adolescent↗
PubMed1998

Functional MRI study of thalamic and cortical activations evoked by cutaneous heat, cold, and tactile stimuli.

Positron emission tomography studies have provided evidence for the involvement of the thalamus and cortex in pain and temperature perception. However, the involvement of these structures in pain and temperature perception of individual subjects has not been studied in detail with high spatial resolution imaging. As a first step toward this goal, we have used functional magnetic resonance imaging (fMRI) to locate discrete regions of the thalamus, insula, and second somatosensory cortex (S2) modulated during innocuous and noxious thermal stimulation. Results were compared with those obtained during tactile stimulation of the palm. High resolution functional images were acquired on a 1.5 T echospeed GE MR system with an in-plane resolution of 1.7 mm. A modified peltier-type thermal stimulator was used to deliver innocuous cool and warm and noxious cold and hot stimuli for 40-60 s to the thenar eminence of normal male and female volunteers. Experimental paradigms consisted of four repetitions of interleaved control and task stimuli. A pixel by pixel statistical analysis of images obtained during each task versus control (e.g., noxious heat vs. warm, warm vs. neutral temperature, etc.) was used to determine task-related activations. Painful thermal stimuli activated discrete regions within the lateral and medial thalamus, and insula, predominantly in the anterior insula in most subjects, and the contralateral S2 in 50% of subjects. The innocuous thermal stimuli did not activate the S2 in any of the subjects but activated the thalamus and posterior insula in 50% of subjects. By comparison, innocuous tactile stimulation consistently activated S2 bilaterally and the contralateral lateral thalamus. These data also demonstrate that noxious thermal and innocuous tactile-related activations overlap in S2. The data also suggest that innocuous and noxious-related activations may overlap within the thalamus but may be located in different regions of the insula. Therefore, we provide support for a role of the anterior insula, S2, and thalamus in the perception of pain; whereas the posterior insula appears to be involved in tactile and innocuous temperature perception. These data demonstrate the feasibility of using fMRI for studies of pain, temperature, and mechanical stimuli in individual subjects, even in small regions such as thalamic nuclei. However, the intersubject variability should be considered in future single subject imaging studies and studies that rely on averaged group responses.

Adult↗
PubMed1997

A longitudinal magnetic resonance imaging study of brain changes in adolescents with anorexia nervosa.

OBJECTIVE: To assess whether the cerebral gray and white matter volume deficits described in patients with anorexia nervosa (AN) are fully reversible with weight rehabilitation. DESIGN: A prospective cohort study using magnetic resonance imaging to examine the brains of female adolescents after weight recovery from AN. SETTING: An adolescent eating disorder program located in a tertiary care children's hospital. PARTICIPANTS: Of 13 patients who underwent a previous magnetic resonance imaging study at a low weight, 6 patients were weight recovered and underwent rescanning. All brain measures were corrected for the effects of intracranial volume and age, based on a regression analysis of a group of 34 healthy female control subjects. Scans from the patients with AN were also compared with scans from an age-matched subset of 16 healthy female controls. MAIN OUTCOME MEASURES: White matter volumes, gray matter volumes, and cerebrospinal fluid volumes in the weight-recovered AN group. RESULTS: Quantitative analysis showed that white matter and ventricular cerebrospinal fluid volumes changed significantly (P = .03 for both) on weight recovery from AN. The weight-recovered patients had significant gray matter volume deficits (P = .01) and elevated cerebrospinal fluid volumes (P = .005) compared with those of the age-matched controls. They no longer had significant (P = .30) white matter volume deficits. CONCLUSION: The finding of persistent gray matter volume deficits in patients who have recovered their weight after AN suggests an irreversible component to the structural brain changes associated with AN, in addition to a component that resolves on weight recovery.

Adolescent↗
PubMed1997

Cerebral gray matter volume deficits after weight recovery from anorexia nervosa.

BACKGROUND: Structural changes have been observed in the brains of low-weight patients with anorexia nervosa (AN), including increased cerebrospinal fluid (CSF) volumes and decreased gray matter and white matter volumes. We hypothesized that subjects who are weight-recovered from AN would show elevated CSF volumes and reduced gray matter volumes compared with controls. METHODS: We used magnetic resonance imaging to compare the brains of 12 subjects who are weight-recovered from AN (time since weight recovery, 1-23 years) with those of 18 healthy control subjects and 13 low-weight patients with AN. Axial, dual-echo scans of the whole brain were segmented into gray matter, white matter, and CSF compartments by means of a computerized volumetric approach. Brain measures were corrected for the significant effects of intracranial volume and age, based on regression analysis of a larger group of 30 healthy female controls. RESULTS: Tests showed that the weight-recovered group had significantly greater CSF volumes and smaller gray matter volumes than the control group. By comparison with low-weight patients, the weight-recovered subjects had significantly smaller CSF volumes and significantly larger gray matter and white matter volumes. In the weight-recovered group, neither the CSF elevations nor gray matter deficits were correlated with the length of time since weight recovery. CONCLUSIONS: The persistent gray matter volume deficits in subjects who are weight-recovered from AN suggest that there may be an irreversible component to the brain changes associated with the illness. The neuropathological features of this irreversible component have yet to be characterized.

Adolescent↗
PubMed1997

Functional magnetic resonance imaging: a potential tool for the evaluation of spinal cord stimulation: technical case report.

OBJECTIVE AND IMPORTANCE: The management of chronic pain of spinal origin continues to represent a challenge for neurosurgeons. Spinal cord stimulation for chronic intractable pain is an effective therapy in approximately 50% of patients. The present study uses a novel imaging approach, functional magnetic resonance imaging (fMRI), to examine the central effects of spinal cord stimulation. CLINICAL PRESENTATION: Three patients, each with a chronic history of intractable pain, were treated at the Toronto Hospital with a trial of dorsal column stimulation (DCS). For all patients, significant improvement in pain symptoms was achieved with DCS. INTERVENTION: fMRI on a 1.5-T conventional magnetic resonance system was used to study the effects of DCS in these patients. Images were collected while the stimulator was activated and deactivated. CONCLUSION: This report is the first to describe the cerebral effects of exogenous spinal cord stimulation with fMRI. fMRI allows for the objective examination of the effects of DCS and may provide an objective means of evaluating the efficacy of DCS as a therapy for intractable pain of spinal origin.

Adult↗
PubMed1997

Functional MRI of pain- and attention-related activations in the human cingulate cortex.

The aims of the study were to use functional magnetic resonance imaging (fMRI) to 1) locate pain-related regions in the anterior cingulate cortex (ACC) of normal human subjects and 2) determine whether each subject's pain-related activation is congruent with ACC regions involved in attention-demanding cognitive processes. Ten normal subjects underwent fMRI with a 1.5-T standard commercial MRI scanner. A conventional gradient echo technique was used to obtain data from a single 4-mm sagittal slice of the left ACC, approximately 3.5 mm from midline. For each subject, interleaved sets of 6 images were obtained during a pain task, an attention-demanding task, and at rest, for a total of 36 images per task. Pain of different intensities was evoked via electrical stimulation of the right median nerve. The attention-demanding task consisted of silent word generation (verbal fluency). Additional experiments obtained data from the right ACC. A pixel-by-pixel statistical analysis of task versus rest images was used to determine task-related activated regions. The pain task resulted in a 1.6-4.0% increase in mean signal intensity within a small region of the ACC. The exact location of this activation varied from subject to subject, but was typically in the posterior part of area 24. The signal intensity changes within this region correlated with pain intensity reported by the subject. The attention-demanding tasks increased the mean signal intensity by 1.3-3.3% in a region anterior and/or superior to the pain-related activation in each subject. The activated region was typically larger than the pain-related activation. In some cases this activation was at or superior to the ACC border, near the supplementary motor area. These regions did not show any pain-intensity-related activation. In one subject both right and left ACC were imaged, revealing bilateral ACC activation during the attention task but only contralateral pain-related activation. These findings shed light on pain- and attention-related cognitive processes. The results provide evidence for a region in the posterior part of the ACC that is involved in pain and a more anterior region involved in other attention-demanding cognitive tasks.

Adult↗
PubMed1996

Cerebral gray matter and white matter volume deficits in adolescent girls with anorexia nervosa.

OBJECTIVES: This study was undertaken to determine whether the increased cerebrospinal fluid (CSF) volumes found in anorexia nervosa (AN) are the result of differences in gray matter or white matter volumes or both. METHODS: Thirteen adolescent girls with AN who were receiving inpatient care at a tertiary-care university children's hospital and eight healthy female control subjects were studied by using magnetic resonance imaging. Images were processed by means of software developed to classify all pixels as either CSF, gray matter, or white matter. Pixels of each class were then summed across all sections. RESULTS: The AN group had larger total CSF volumes in association with deficits in both total gray matter and total white matter volumes. Lowest reported body mass index was inversely correlated with total CSF volume and positively correlated with total gray matter volume. Urinary free cortisol levels were positively correlated with total CSF volume and inversely correlated with central gray matter volume. CONCLUSIONS: These findings add support to the view that the brain abnormalities found in AN are in large part the result of the effects of the illness. The extent to which these differences in gray matter and white matter volumes are reversible with recovery remains to be established.

Adolescent↗
PubMed1996

Endurance-trained and untrained skeletal muscle bioenergetics observed with magnetic resonance spectroscopy.

Resting and submaximal isometric exercise 31P magnetic resonance spectroscopy (MRS) was carried out on 7 endurance-trained males (26.0 +/- 3 yrs) and 7 sedentary males (27.0 +/- 4 yrs). Spectral analysis provided peak areas of phosphocreatine (PCr), inorganic phosphate (Pi), adenosine triphosphate (ATP), and the chemical shift of Pi relative to PCr. The ratio of PCr/Pi was moderately lower during rest (preexercise p = .13, postexercise p = .18), and significantly higher during exercise (p < .05) in the trained subjects. Intracellular pH patterns were the same for both groups; a transient alkalosis was observed at the onset of exercise with a return to resting levels after 2 min. Differences suggest improved ATP resynthesis rate in the trained subjects during exercise. Intracellular pH changes can be attributed to the utilization of hydrogen ions that accompany PCr hydrolysis during work. The findings are congruent with previous reports indicating a superior oxidative capacity in trained skeletal muscle.

Adenosine Triphosphate↗
PubMed1995

fMRI of human somatosensory and cingulate cortex during painful electrical nerve stimulation.

Functional MRI (fMRI) can detect changes from resting levels of blood flow and oxygenation during task performance (i.e. activation). We used a simple electrical nerve stimulation technique together with fMRI to study pain process in the human cortex. Images of the primary somatosensory (SI) and cingulate cortex (Cg) were obtained from subjects during stimulation at painful and non-painful intensities. Stimuli that evoked non-painful tingling sensations activated the contralateral SI but not Cg. Stimuli that evoked painful sensations activated both the contralateral SI and Cg. These data indicate that fMRI can detect pain-related changes in SI and Cg evoked by electrical stimulation of peripheral nerves. These findings add to the evidence for a role of SI and Cg in human pain processes and provide a simple method of stimulus delivery for its study.

Adult↗
PubMed1995

Quantitation of articular cartilage using magnetic resonance imaging and three-dimensional reconstruction.

A quadrature knee coil was used in conjunction with a magnetic resonance imaging scanner for quantitation of test phantom volumes, ex vivo bovine cartilage thickness, and in vivo human articular cartilage volumes. Optimal magnetic resonance parameters were obtained by testing a series of spin-echo and gradient-echo pulse sequences to determine the sequence that provided the highest resolution of articular cartilage and best defined the cartilage interfaces with synovial fluid and subchondral bone. Extensive testing revealed that two sequences were required to define articular cartilage accurately: a spoiled gradient-echo sequence and a steady state free-precession sequence. Three-dimensional reconstruction and statistical analyses of test phantoms and of bovine and human cartilage images were performed. Differences between actual phantom volumes and three-dimensional measurements demonstrated that, as magnetic resonance slice thickness was increased, the measurement variability also increased (coefficient of variation ranging from 1.7 +/- 1.3% for 1.0 mm slice thickness to 22.7 +/- 1.9% for 3.0 mm slice thickness). When the phantom volume was greater than 1,800 mm3, the intraobserver, interobserver and interscan accuracies were greater than 97, 98, and 96%, respectively. This high degree of reproducibility pertained for the data on in vivo human cartilage data also. For experienced observers, the intraobserver and interobserver reproducibility were greater than 98 and 97%, respectively. The interscan reproducibility was greater than 98%. These data demonstrate that improved magnetic resonance pulse sequencing, in conjunction with three-dimensional reconstruction and measurement techniques, can accurately and reproducibly measure the volume of articular cartilage. Clinical application of this approach offers the potential for early diagnosis of osteoarthritis and for serial, noninvasive assessment of changes in articular cartilage volume in response to therapeutic modalities.

Adult↗
PubMed1994

Oscillatory motion of the normal cervical spinal cord.

PURPOSE: To determine the normal pattern of cervical spinal cord motion with measurement of cervical spinal cord velocity by means of phase-contrast magnetic resonance (MR) imaging. MATERIALS AND METHODS: Spinal cord velocity was measured in 11 healthy subjects with a modified gradient-echo pulse sequence on a conventional 1.5-T MR imaging system that generated phase images sensitive to slow motion. Prospective electrocardiogram gating was used to assess velocity as a function of the cardiac cycle. The accuracy of velocity measurements was estimated with images of a phantom moving at constant velocity. RESULTS: The cervical spinal cord moves with an oscillatory pattern in the craniocaudal direction. The maximum velocity (7.0 mm/sec +/- 1.4 [standard deviation]) in the caudal direction occurred approximately 109 msec +/- 20 after electrical cardiac systole. The maximum velocities in subsequent oscillations decreased toward zero before the next cardiac systole. CONCLUSION: The cervical spinal cord oscillates in a craniocaudal direction after each cardiac systole.

Adult↗