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Biomedical subjects

G McCarthy

Publications and source records attributed to G McCarthy.

At least 73 records · Page 4Linked to original sources
PubMed1998

Dissociation of mnemonic and perceptual processes during spatial and nonspatial working memory using fMRI.

Neuroimaging studies in humans have consistently found robust activation of frontal, parietal, and temporal regions during working memory tasks. Whether these activations represent functional networks segregated by perceptual domain is still at issue. Two functional magnetic resonance imaging experiments were conducted, both of which used multiple-cycle, alternating task designs. Experiment 1 compared spatial and object working memory tasks to identify cortical regions differentially activated by these perceptual domains. Experiment 2 compared working memory and perceptual control tasks within each of the spatial and object domains to determine whether the regions identified in experiment 1 were driven primarily by the perceptual or mnemonic demands of the tasks, and to identify common brain regions activated by working memory in both perceptual domains. Domain-specific activation occurred in the inferior parietal cortex for spatial tasks, and in the inferior occipitotemporal cortex for object tasks, particularly in the left hemisphere. However, neither area was strongly influenced by task demands, being nearly equally activated by the working memory and perceptual control tasks. In contrast, activation of the dorsolateral prefrontal cortex and the intraparietal sulcus (IPS) was strongly task-related. Spatial working memory primarily activated the right middle frontal gyrus (MFG) and the IPS. Object working memory activated the MFG bilaterally, the left inferior frontal gyrus, and the IPS, particularly in the left hemisphere. Finally, activation of midline posterior regions, including the cingulate gyrus, occurred at the offset of the working memory tasks, particularly the shape task. These results support a prominent role of the prefrontal and parietal cortices in working memory, and indicate that spatial and object working memory tasks recruit differential hemispheric networks. The results also affirm the distinction between spatial and object perceptual processing in dorsal and ventral visual pathways.

Adult↗
PubMed1997

Magnetic resonance imaging-based measurement of hippocampal volume in posttraumatic stress disorder related to childhood physical and sexual abuse--a preliminary report.

We have previously reported smaller hippocampal volume and deficits in short-term memory in patients with combat-related posttraumatic stress disorder (PTSD) relative to comparison subjects. The purpose of this study was to compare hippocampal volume in adult survivors of childhood abuse to matched controls. Magnetic resonance imaging was used to measure volume of the hippocampus in adult survivors of childhood abuse (n = 17) and healthy subjects (n = 17) matched on a case-by-case basis for age, sex, race, handedness, years of education, body size, and years of alcohol abuse. All patients met criteria for PTSD secondary to childhood abuse. PTSD patients had a 12% smaller left hippocampal volume relative to the matched controls (p < .05), without smaller volumes of comparison regions (amygdala, caudate, and temporal lobe). The findings were significant after controlling for alcohol, age, and education, with multiple linear regression. These findings suggest that a decrease in left hippocampal volume is associated with abuse-related PTSD.

Adult↗
PubMed1997

Childhood adversities and psychosocial disorders.

Adverse childhood experiences--especially inadequacies in early parental care--are associated with elevated rates of both acute and chronic psychosocial disorders in adult life. In most instances, adverse outcomes are confined to a minority of children exposed; variations in the severity or pervasiveness of early risk, individual differences in susceptibility, and interactions with later stressors are all thus likely to be important in mediating effects. At present, knowledge of intervening processes is limited, and dependent on retrospective studies of adult samples or short-term longitudinal findings in childhood. We review current evidence on the long-term outcomes of prenatal divorce, childhood maltreatment, and institutional rearing, and on the early antecedents of depression and antisocial behaviour in adult life, to highlight possible interviewing mechanisms. Most long-term sequelae seem likely to depend on a series of shorter-term links, some running through elevated risks of continued environmental adversity, others through psychological vulnerabilities and problems in social relationships.

Adult↗
PubMed1997

Filaroides hirthi verminous pneumonia in a West Highland white terrier bred in Ireland.

A two-year-old West Highland white terrier, which had failed to thrive from six months of age, presented with acute onset dyspnoea. Radiography showed a diffuse pulmonary infiltrate throughout both lungs. Haematological abnormalities were an absolute neutrophilia and eosinophilia. Postmortem examination revealed uniform consolidation of both lungs which was defined histologically as a verminous granulomatous pneumonia. Metastrongyle larvae, isolated from the pulmonary tissue, had the morphological characteristics of Filaroides species. On the basis of the pathological changes and the larval morphology, a presumptive diagnosis of F hirthi pneumonia was made. This is believed to be the first report of disease due to this parasite in Ireland.

Animals↗
PubMed1997

Infrequent events transiently activate human prefrontal and parietal cortex as measured by functional MRI.

P300 is an event-related potential elicited by infrequent target events whose amplitude is dependent on the context provided by the immediately preceding sequence of stimuli, suggesting its dependence on working memory. We employed magnetic resonance imaging sequences sensitive to blood oxygenation level to identify regional changes evoked by infrequent visual target stimuli presented in a task typically used to elicit P300. Targets evoked transient event-related activation bilaterally in the middle frontal gyrus, in the inferior parietal lobe, and near the inferior aspect of the posterior cingulate gyrus beginning within 1.5 s of target onset and peaking between 4.5 and 6 s. These regions have been identified in previous neuroimaging studies in humans, and in single-unit recordings in monkeys, as components of a neural system mediating working memory, which suggests that this system may be activated by the same events that evoke P300.

Adult↗
PubMed1997

Cerebral vascular malformations adjacent to sensorimotor and visual cortex. Functional magnetic resonance imaging studies before and after therapeutic intervention.

BACKGROUND AND PURPOSE: It is not known how cerebral vascular malformations affect the function of the surrounding brain. Functional magnetic resonance imaging (fMRI) can provide information about normal functional neuroanatomy and its alteration by vascular lesions and therapeutic intervention. METHODS: We performed fMRI studies in 24 patients harboring vascular malformations adjacent to primary somatosensory, motor, and visual cortex. The fMRI studies consisted of the acquisition of an image time series coupled with functional activation of motor, sensory, or visual cortex in both hemispheres. Activated voxels were identified using frequency domain analyses, and their number and anatomic location were compared between the affected and unaffected hemispheres. RESULTS: Every patient capable of performing the desired task showed functional activation. Eight patients without neurological deficits showed a symmetrical pattern of activation between the hemispheres. Each had a vascular malformation located one or more gyri from the functional region imaged. Three patients showed hemispheric symmetry in the location of activated cortex but with a marked asymmetry in the number of activated voxels. Each harbored vascular malformations located within one gyrus of the functional region and showed either subtle or no neurological deficit. Eleven patients showed hemispheric asymmetry in the location of activated cortex. In 6, the anatomic displacement appeared to be due to a mass effect of the lesion. In 5, the activation occurred at a different anatomic locale, and the patients exhibited gross neurological deficit in the respective function. Posttherapeutic changes in functional activation reflected elimination of the mass effect or recovery of clinical function. CONCLUSIONS: Systematic fMRI studies are possible in patients with vascular malformations in brain regions adjacent to primary somatosensory, motor, and visual cortex. Displacement of the activated region and hemispheric asymmetry in the number of activated voxels in the functional regions appear to reflect the anatomic and physiological impact of the vascular malformation. Changes in fMRI findings after intervention reflect the consequences of therapy and parallel clinical recovery.

Adolescent↗
PubMed1997

Resistance to neuroglycopenia: an adaptive response during intensive insulin treatment of diabetes.

Counterregulation and awareness of hypoglycemia begins at lower plasma glucose levels in insulin-dependent diabetes mellitus (IDDM) subjects given intensive insulin treatment. To determine whether these changes are associated with an alteration in the susceptibility of the brain to mild hypoglycemia, we compared central nervous system responses to hypoglycemia in 8 intensively treated (hemoglobin A1, 8.3 +/- 0.2%; normal, <8%) and 11 conventionally treated IDDM patients (hemoglobin A1, 14.6 +/- 1.3%) with those in 10 healthy subjects. Plasma glucose was lowered from approximately 4.6 mmol/L in 0.5-0.6 steps using the clamp technique. Glucose levels triggering hormonal responses and perception of hypoglycemic symptoms were significantly lower in intensively treated patients compared to their poorly controlled counterparts (P < 0.05), and hormonal responses were suppressed compared to those in healthy controls. Similarly directed changes occurred in the level of circulating glucose required to alter cortical evoked potentials during hypoglycemia. A greater reduction in plasma glucose was required to alter P300 event-related potentials in the intensively treated patients (2.2 mmol/L) compared to those in the conventionally treated and nondiabetic groups (approximately 3.5 and approximately 3.0 mmol/L, respectively). We conclude that intensively treated IDDM patients are resistant to changes in cortical evoked potentials induced by mild hypoglycemia. This may explain why intensively treated IDDM counterregulate and experience hypoglycemic symptoms at a lower glucose level than conventionally treated patients.

Adaptation, Physiological↗
PubMed1997

Surface and depth EEG findings in patients with hippocampal atrophy.

OBJECTIVE: To establish if MRI evidence of hippocampal atrophy (HcA) is an independent surrogate of EEG criteria for the diagnosis of medial temporal lobe (MTL) epilepsy (MTLE). BACKGROUND: MRI evidence of HcA has been shown to correlate with mesial temporal sclerosis (MTS), intracranial evidence of MTL seizure onset, and outcome after temporal lobectomy. The reported rate of discordance between scalp ictal EEG recordings and MRI evidence of unilateral HcA ranges from rare to moderate. We examined the surface and depth ictal EEG findings of patients with HcA, as detected by volumetric MRI, to clarify their significance in detecting areas of epileptogenicity in this group of patients. METHODS: From a group of patients with refractory epilepsy, we identified 119 patients with HcA (97 with unilateral and 13 with bilateral HcA, 9 with HcA and mass lesion). MRI volumetric studies were used to obtain Hc ratios. Absolute volumes were used to detect bilateral atrophy. Surface and depth EEG recordings were analyzed for localization of ictal abnormalities, and their distribution was compared for concordance with the location of HcA. Surgical outcome was reviewed. RESULTS: Of the 110 patients with isolated HcA, 63 had surgery; 82% of ictal depth EEG onsets were concordant with the atrophic Hc, and 72% ictal surface EEG onsets were concordant. Four patients with concordant EEG and HcA failed to achieve seizure control with resection of the atrophic Hc. Furthermore, 3 patients with discordant EEG and HcA had resection of the non-atrophic Hc with excellent results. Among the 47 non-operated patients, 54% had discordant or unlocalized ictal depth EEG results and 52% had discordant ictal surface EEG. Four of the 9 lesional patients with HcA had excellent outcome after lesionectomy without hippocampectomy. CONCLUSION: The presence of HcA is not an independent predictor of the site of epileptogenesis.

Amygdala↗
PubMed1996

Differential sensitivity of human visual cortex to faces, letterstrings, and textures: a functional magnetic resonance imaging study.

Twelve normal subjects viewed alternating sequences of unfamiliar faces, unpronounceable nonword letterstrings, and textures while echoplanar functional magnetic resonance images were acquired in seven slices extending from the posterior margin of the splenium to near the occipital pole. These stimuli were chosen to elicit initial category-specific processing in extrastriate cortex while minimizing semantic processing. Overall, faces evoked more activation than did letterstrings. Comparing hemispheres, faces evoked greater activation in the right than the left hemisphere, whereas letterstrings evoked greater activation in the left than the right hemisphere. Faces primarily activated the fusiform gyrus bilaterally, and also activated the right occipitotemporal and inferior occipital sulci and a region of lateral cortex centered in the middle temporal gyrus. Letterstrings primarily activated the left occipitotemporal and inferior occipital sulci. Textures primarily activated portions of the collateral sulcus. In the left hemisphere, 9 of the 12 subjects showed a characteristic pattern in which faces activated a discrete region of the lateral fusiform gyrus, whereas letterstrings activated a nearby region of cortex within the occipitotemporal and inferior occipital sulci. These results suggest that different regions of ventral extrastriate cortex are specialized for processing the perceptual features of faces and letterstrings, and that these regions are intermediate between earlier processing in striate and peristriate cortex, and later lexical, semantic, and associative processing in downstream cortical regions.

Adult↗
PubMed1996

Localization of functional regions of human mesial cortex by somatosensory evoked potential recording and by cortical stimulation.

We describe methods of localizing functional regions of the mesial wall, based on 47 patients studied intraoperatively or following chronic implantation of subdural electrodes. Somatosensory evoked potentials were recorded to stimulation of posterior tibial, dorsal pudendal, median, and trigeminal nerves. Bipolar cortical stimulation was performed, and in 4 cases movement-related potentials were recorded. The cingulate and marginal sulci formed the inferior and posterior borders of the sensorimotor areas and the supplementary motor area (SMA). The foot sensory area occupied the posterior paracentral lobule, while the genitalia were represented anterior to the foot sensory area, near the cingulate sulcus. The foot motor area was interior and superior to the sensory areas, but there was overlap in these representations. There was a rough somatotopic organization within the SMA, with the face represented anterior to the hand. However, there was little evidence of the "pre-SMA" region described in monkeys. Complex movements involving more than one extremity were elicited by stimulation of much of the SMA. The region comprising the supplementary sensory area was not clearly identified, but may involve much of the precuneus. Movement-related potentials did not provide additional localizing information, although in some recordings readiness potentials were recorded from the SMA that appeared to be locally generated.

Adolescent↗
PubMed1996

Paediatricians' knowledge of cardiac arrest guidelines.

A telephone questionnaire was undertaken on middle grade trainee paediatricians to test their knowledge of European Resuscitation Council guidelines. Fifty seven responded of whom only 15 (26%) offered a correct sequence of management for asystole and eight (14%) failed to identify adrenaline in their management. For ventricular fibrillation only 18/57 (32%) identified a correct sequence and very poor specific knowledge was identified. Paediatricians will under perform in the event of cardiac arrest in children without improved training in resuscitation.

Child↗
PubMed1996

Magnetic resonance imaging studies of functional brain activation: analysis and interpretation.

We have demonstrated that a time series of echoplanar images can contain low frequency noise components which confound analysis of functional MRI data. In simulated tasks of long duration, the false positive rate from t-test analyses greatly exceeded the statistical probability level. As task durations were shortened, the false positive rate declined. We also demonstrated that voxels representing extensive regions of the brain covary significantly over time. This covariation challenges the independence assumption of t-test and other analytical procedures and likely contributes to the false positive rate. The frequency spectra of many voxels showed relatively little power at higher frequencies with the important exception of some blood vessels (Fig. 12). Experimental designs in which stimulus or task conditions were alternated at these higher frequencies (e.g. 0.083 Hz corresponding to a 6 sec task duration and a 12 sec period for a complete two task cycle) did not show an inflated false positive rate when analyzed by t-test. We used the alternating tasks design with task durations of 8.73 sec, 6.4 sec, and 6.0 sec coupled with a frequency domain analysis strategy in a series of somatosensory, motor, perceptual, and working memory experiments. This combination of design and analysis was successful in identifying reliable activations across groups of subjects with a minimum of apparently spurious activations. By introducing a 180 degrees phase shift by reversing task order, we have been able to eliminate the contribution of most high frequency noise sources (such as large blood vessels). By segregating low frequency noise from the frequency of stimulus alternation, we routinely generate stable results in the presence of low frequency noise and drift. Despite the usefulness of the rapid task alternation and frequency domain techniques demonstrated here, there are potential problems and limitations in their application: 1. The short duration of our tasks results in an approximately sinusoidal activation waveform. With longer duration tasks, the activation time course would appear more square with a more complex frequency spectrum than the single peak demonstrated above. In such circumstances we have used convolution analysis with an expected waveform (McCarthy et al. 1996), similar to the approach of Bandettini et al. (1993). 2. If the activation in one task condition is significantly delayed and extends well into the period of the second task, it will be difficult to determine which task produced the activation. This problem is not specific to frequency analysis, and would occur as well for t-tests. One solution we have used is running a single active task against a relatively neutral control such as fixation to determine the usual activation dynamics of the active task. 3. Common activations by two alternating tasks are de-emphasized. This problem is also not specific to frequency analysis, and in most circumstances is an advantage rather than a disadvantage. However, if uncertain as to whether a task is capable of producing any activation, we have again used the strategy of running the task against a relatively neutral control. 4. Some tasks do not lend themselves to the short durations used here. 5. The frequency domain procedures used are conservative and may underestimate the true anatomical extent of the activation. In practice we compute t-tests in addition to the frequency domain techniques to guard against this possibility. Many of the advantages of the procedures described here are due to the alternation of short duration tasks rather than the application of frequency domain techniques per se. However, the success of these techniques in isolating periodic task-related signal changes suggest that a more complex design with concurrent stimulation presented at different frequencies might be feasible. Such designs may have advantages in that categories of stimuli would not be presented in isolation but against a changing ba

Artifacts↗
PubMed1995

Deficits in short-term memory in adult survivors of childhood abuse.

Exposure to stress has been associated with alterations in memory function, and we have previously shown deficits in short-term verbal memory in patients with a history of exposure to the stress of combat and the diagnosis of posttraumatic stress disorder (PTSD). Few studies of any kind have focused on adult survivors of childhood physical and sexual abuse. The purpose of this study was to investigate short-term memory function in adult survivors of childhood abuse. Adult survivors of severe childhood physical and sexual abuse (n = 21), as defined by specific criteria derived from the Early Trauma Inventory (ETI), who were presenting for psychiatric treatment were compared with healthy subjects (n = 20) matched for several variables including age, alcohol abuse, and years of education. All subjects were assessed with the Wechsler Memory Scale (WMS) Logical (verbal memory) and Figural (visual memory) components, the Verbal and Visual Selective Reminding Tests (SRT), and the Wechsler Adult Intelligence Scale-Revised (WAIS-R). Adult survivors of childhood abuse had significantly lower scores on the WMS Logical component for immediate and delayed recall in comparison to normal subjects, with no difference in visual memory, as measured by the WMS or the SRT, or IQ, as measured by the WAIS-R. Deficits in verbal memory, as measured by the WMS, were associated with the severity of abuse, as measured by a composite score on the ETI. Our findings suggest that childhood physical and sexual abuse is associated with long-term deficits in verbal short-term memory. These findings of specific deficits in verbal (and not visual) memory, with no change in IQ, are similar to the pattern of deficits that we have previously found in patients with combat-related PTSD.

Adult↗