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Biomedical subjects

G L Ahern

Publications and source records attributed to G L Ahern.

At least 19 recordsLinked to original sources
PubMed2001

Temporal lobe seizure interhemispheric propagation time depends on nonepileptic cortical cerebral blood flow.

In some patients with epilepsy, activation of eloquent cortex using various forms of environmental stimulation and mental activity may induce seizures. The increased neuronal activity resulting from cortical stimulation may be associated with increased regional cerebral blood flow. The vascular steal theory of temporal lobe epilepsy suggests that as nonepileptogenic cortical cerebral blood flow (CBFn) increases, temporal lobe epileptogenicity increases as a result, in part, of decreasing interhemispheric propagation time (IHPT). Recently, IHPT has been shown to be a quantitative electrocorticographic measure of temporal lobe epileptogenicity. In the current study, long-term combined subdural-EEG and surface cortical cerebral blood flow (CBF) monitoring was performed to test the hypothesis that IHPT depends upon CBFn. The results show that IHPT is a nonlinear (negative exponential) function of nonepileptic cortical CBF (r=0.507, df=32, t=-2.204, P<0.05). In temporal lobe epilepsy, nonepileptic cortical hypoperfusion may represent a protective mechanism for delaying interhemispheric seizure propagation. The fact that IHPT decreases exponentially with increasing CBFn suggests that small increases in CBFn should substantially decrease IHPT and increase epileptogenicity. This study confirms that inter-hemispheric propagation time depends upon perfusion of nonepileptogenic cortex.

Adolescent↗
PubMed2001

Heart rate and heart rate variability changes in the intracarotid sodium amobarbital test.

PURPOSE: Changes in heart rate and heart rate variability have been found in prior studies performed during the intracarotid sodium amobarbital (ISA) test. However, these results are not entirely consistent with current models of differential cerebral involvement in the modulation of the heart. This study was designed to re-investigate this topic with a larger N than has heretofore been used. METHODS: The electrocardiogram was recorded during left and right ISAs in 73 subjects. Raw heart rate and heart rate variability were calculated. RESULTS: Raw heart rate increased during inactivation of either hemisphere, but more so for the right hemisphere. Heart rate variability changes consistent with decreasing parasympathetic tone also were found to occur during either ISA, but to a significant degree, only during right ISA. CONCLUSIONS: The right hemisphere appears to have a greater role in cerebral regulation of cardiac function, perhaps by virtue of the modification of parasympathetic effects.

Adolescent↗
PubMed2001

Time from ictal subdural EEG seizure onset to clinical seizure onset: prognostic value for selecting temporal lobectomy candidates.

Long-term subdural EEG recording was performed to test the hypothesis that the duration from ictal subdural EEG seizure onset (ECOT) is prognostic for seizure-free outcome following temporal lobectomy. In 48 patients with complex partial seizures, temporal lobectomy was based on invasive localization of the ictal seizure focus. Subdural EEG data were analyzed for association with seizure-free outcome (seizure-free: yes or no) at a minimum of one year following temporal lobectomy. As the duration from ictal subdural EEG seizure onset to clinical seizure onset increased, the odds of being seizure-free postoperatively increased. The best fitting statistical model for predicting seizure-free outcome included seizure onset (unilateral vs. bilateral) and duration from ictal subdural EEG seizure onset to clinical seizure onset. While selection of temporal lobectomy candidates has increasingly emphasized noninvasive recording, some scalp-EEG monitored patients cannot be offered surgery for various reasons, one of which may include ictal EEG seizure onset following clinical seizure onset. When subdural EEG monitoring is performed for selection of temporal lobectomy candidates, analysis of the duration from subdural EEG seizure onset to clinical seizure onset should improve the prognostic value of the subdural EEG data for seizure-free outcome following temporal lobectomy.

Adolescent↗
PubMed2000

Affective self-report during the intracarotid sodium amobarbital test: group differences.

Emotional reactions are sometimes observed during the intracarotid sodium amobarbital test. For instance, euphoric/indifference reactions can be seen during right hemisphere inactivation and catastrophic reactions may accompany left hemisphere inactivation. Less dramatic changes can also be detected in affective self-report during left and right hemisphere amobarbital tests, with more negative affect reported during left hemisphere inactivation and either neutral or mildly positive affective states reported during right hemisphere inactivation. The current study not only replicated this effect, but in addition, found significant group differences. The first group (right way) showed a pattern of affective self-report during left and right amobarbital tests entirely consistent with prior findings, while a second group (wrong way) showed results that behaved in a diametrically opposite fashion. A third group (no change) showed little, if any, difference in affective self-report during left and right amobarbital tests. The major factor distinguishing the wrong way group from the other two appeared to be an asymmetrical distribution of left and right temporal lobe lesions in the former group. In contrast, the factor differentiating the right way group from the no change group appeared to be the relative degree of left hemisphere inactivation during the left hemisphere amobarbital test. The results are discussed not only in terms of their impact on theories of cerebral lateralization for emotion, but also in terms of methodological issues in this field.

Adolescent↗
PubMed1998

Quantitative analysis of hemispatial neglect in the intracarotid sodium amobarbital (ISA) test.

There are dramatic changes in the electroencephalogram of the inactivated hemisphere in the intracarotid sodium amobarbital test. One of the more profound behavioral changes during this procedure is left hemispatial neglect accompanying right hemisphere inactivation. The present study was designed to ascertain whether there was a clear relationship between the degree of hemispheric inactivation (as measured by the electroencephalogram) and the degree of left hemispatial neglect during this procedure. Sixty-nine participants undergoing right hemisphere intracarotid sodium amobarbital testing were presented with a random letter cancellation test at various points during the procedure. Neglect was quantified as significant, moderate, minimal, or none, based on how many target letters the patients missed. The simultaneous electroencephalogram from each of these testing points was spectrally analyzed and topographic maps were generated. The degree of neglect was then compared with the comparable topographic map. It was found that as the amobarbital-induced right hemispheric dysfunction regressed, the degree of neglect lessened in a systematic fashion, as did the profound electroencephalographic changes induced by the drug. Thus, there is a clear relation between the degree of hemispheric inactivation induced by the amobarbital and the degree of left hemispatial neglect. This relationship held regardless of side of hemispheric language dominance or epileptic focus. These results replicate previous findings that right hemisphere inactivation during the intracarotid sodium amobarbital test results in left hemispatial neglect. They extend these findings by clearly showing that neglect changes in a quantitative fashion (rather than being an all-or-none phenomenon) and further, show that there is a clear relationship between the severity of neglect and the degree of hemispheric dysfunction.

Adolescent↗
PubMed1997

Neuroanatomical correlates of pleasant and unpleasant emotion.

Substantial evidence suggests that a key distinction in the classification of human emotion is that between an appetitive motivational system association with positive or pleasant emotion and an aversive motivational system associated with negative or unpleasant emotion. To explore the neural substrates of these two systems, 12 healthy women viewed sets of pictures previously demonstrated to elicit pleasant, unpleasant and neutral emotion, while positron emission tomographic (PET) measurements of regional cerebral blood flow were obtained. Pleasant and unpleasant emotions were each distinguished from neutral emotion conditions by significantly increased cerebral blood flow in the vicinity of the medial prefrontal cortex (Brodmann's area 9), thalamus, hypothalamus and midbrain (P < 0.005). Unpleasant was distinguished from neutral or pleasant emotion by activation of the bilateral occipito-temporal cortex and cerebellum, and left parahippocampal gyrus, hippocampus and amygdala (P < 0.005). Pleasant was also distinguished from neutral but not unpleasant emotion by activation of the head of the left caudate nucleus (P < 0.005). These findings are consistent with those from other recent PET studies of human emotion and demonstrate that there are both common and unique components of the neural networks mediating pleasant and unpleasant emotion in healthy women.

Adolescent↗
PubMed1997

Neuroanatomical correlates of externally and internally generated human emotion.

OBJECTIVE: Positron emission tomography was used to investigate the neural substrates of normal human emotional and their dependence on the types of emotional stimulus. METHOD: Twelve healthy female subjects underwent 12 measurements of regional brain activity following the intravenous bolus administration of [15O]H2O as they alternated between emotion-generating and control film and recall tasks. Automated image analysis techniques were used to characterize and compare the increases in regional brain activity associated with the emotional response to complex visual (film) and cognitive (recall) stimuli. RESULTS: Film- and recall-generated emotion were each associated with significantly increased activity in the vicinity of the medial prefrontal cortex and thalamus, suggesting that these regions participate in aspects of emotion that do not depend on the nature of the emotional stimulus. Film-generated emotion was associated with significantly greater increases in activity bilaterally in the occipitotemporparietal cortex, lateral cerebellum, hypothalamus, and a region that includes the anterior temporal cortex, amygdala, and hippocampal formation, suggesting that these regions participate in the emotional response to certain exteroceptive sensory stimuli. Recall-generated sadness was associated with significantly greater increases in activity in the vicinity of the anterior insular cortex, suggesting that this region participates in the emotional response to potentially distressing cognitive or interoceptive sensory stimuli. CONCLUSIONS: While this study should be considered preliminary, it identified brain regions that participate in externally and internally generated human emotion.

Adult↗
PubMed1997

Neuroanatomical correlates of happiness, sadness, and disgust.

OBJECTIVE: Happiness, sadness, and disgust are three emotions that differ in their valence (positive or negative) and associated action tendencies (approach or withdrawal). This study was designed to investigate the neuroanatomical correlates of these discrete emotions. METHOD: Twelve healthy female subjects were studied. Positron emission tomography and [15O]H2O were used to measure regional brain activity. There were 12 conditions per subject: happiness, sadness, and disgust and three control conditions, each induced by film and recall. Emotion and control tasks were alternated throughout. Condition order was pseudo-randomized and counterbalanced across subjects. Analyses focused on brain activity patterns for each emotion when combining film and recall data. RESULTS: Happiness, sadness, and disgust were each associated with increases in activity in the thalamus and medial prefrontal cortex (Brodmann's area 9). These three emotions were also associated with activation of anterior and posterior temporal structures, primarily when induced by film. Recalled sadness was associated with increased activation in the anterior insula. Happiness was distinguished from sadness by greater activity in the vicinity of ventral mesial frontal cortex. CONCLUSIONS: While this study should be considered preliminary, it identifies regions of the brain that participate in happiness, sadness, and disgust, regions that distinguish between positive and negative emotions, and regions that depend on both the elicitor and valence of emotion or their interaction.

Adult↗
PubMed1996

Right sided hemispatial neglect and bilateral cerebral lesions.

This study compared the frequency with which unilateral and bilateral cerebral disease gives rise to right sided visual hemispatial inattention. A retrospective survey identified brain injured patients for whom target omissions on visual target cancellation tasks significantly exceeded control values. Subjects consisted of 40 right handed patients referred for clinical evaluation or research study of hemispatial inattention. Right sided visual hemispatial inattention occurred with greater frequency and severity in patients with bilateral lesions than in patients with unilateral left sided or right sided lesions. All eight patients with bilateral lesions manifested right sided hemispatial inattention and failed to detect more targets overall than patients in the other two groups. Of the 13 patients with left sided lesion, seven ignored more targets on the right and six ignored more targets on the left. All but one of the 19 patients with right sided lesions ignored more targets on the left. The association of severe right sided visual hemispatial inattention with bilateral cerebral disease extends previous findings and showed that, in this sample, the most common setting for right sided hemispatial neglect occurred in patients with bilateral cerebral lesions.

Aged↗
PubMed1995

Response of human epileptic temporal lobe cortical blood flow to hyperventilation.

Bilateral long-term surface cortical cerebral blood flow (CBF) and electrocorticographic (ECoG) monitoring were performed in eight patients with complex partial seizures. In each patient, the epileptic temporal lobe was localized using ictal ECoG. Mean seizure interval (frequency-1) off anticonvulsant medication, a clinical measure of epileptogenicity, was 1.0 +/- 0.3 h (range: 0.4 to 2.5 h). During 13 interictal hyperventilation periods, 3.6 +/- 0.6 min in duration, the mean decrease in epileptic and nonepileptic temporal cortical CBF was 13.7 +/- 2.3 versus 6.4 +/- 1.9 ml/(100 g min) (t = 2.230, d.f. = 16, P < 0.05), representing 20.9% and 10.8% reduction from baseline CBF during hyperventilation, respectively. Seizure interval decreased (i.e. frequency increased) with increasing magnitude of seizure focus CBF reduction during hyperventilation. Seizure interval was significantly correlated with epileptic temporal lobe CBF decrease during hyperventilation (R = 0.763, d.f. = 5, P < 0.05). The data suggest that, compared to nonepileptic brain, epileptic temporal lobe is particularly prone to hypoperfusion during hyperventilation. Epileptogenicity is a function of this seizure focus susceptibility to ischemia. The finding of abnormal seizure focus autoregulation during hyperventilation has implication for epileptic focus localization with cerebral blood flow analysis.

Adolescent↗
PubMed1995

Quantitative analysis of the electroencephalogram in the intracarotid amobarbital procedure: II. Coherence analysis.

Thirty-seven subjects underwent bilateral internal carotid artery injections of amobarbital before surgery for intractable epilepsy. The electroencephalograms (EEG) of these patients were continuously monitored during these 74 procedures and were later subjected to quantitative analysis. Analysis of interhemispheric coherence in the delta, theta, alpha, and beta 1 bands was performed. Prominent changes occurred in interhemispheric coherence, which showed a precipitous drop in the first 2 min after amobarbital injection, followed by a gradual return to near baseline levels. These results suggest that interhemispheric relationships are significantly disrupted by intracarotid amobarbital injection.

Adolescent↗
PubMed1994

Quantitative analysis of the EEG in the intracarotid amobarbital procedure. I. Amplitude analysis.

Thirty-seven subjects underwent bilateral internal carotid artery injections of amobarbital prior to surgery for intractable epilepsy. The electroencephalogram (EEG) of these patients was continuously monitored during these 74 procedures and was later subjected to quantitative analysis. Topographic mapping of these data suggested that the areas of inactivation were largely restricted to the anterior 2/3 of the hemisphere injected, corresponding to the vascular distributions of the anterior and middle cerebral arteries. Graphical representation of the data demonstrated that delta and theta band activity peaked in the first 2 min post injection and decreased gradually thereafter, becoming stable at around 12 min post injection. Examination of the alpha, beta 1, and beta 2 bands suggested that activity increased and decreased more gradually than that for delta and theta, with perhaps a longer latency. Although EEG changes were most prominent in the anterior 2/3 of the inactivated hemisphere, similar (though smaller) changes were also observed in both ipsilateral and contralateral zones thought to be outside of the vascular distribution of the internal carotid artery.

Adolescent↗
PubMed1994

Affective self-report during the intracarotid sodium amobarbital test.

Changes in internal affective state were investigated in patients undergoing the intracarotid sodium amobarbital test. It was found that when the left hemisphere was inactivated, patients rated their mood as significantly more negative than during baseline conditions. No significant change in affective state was observed during the inactivation of the right hemisphere. The findings are interpreted in terms of a differential lateralization model of emotion, in which the right hemisphere is more involved in the more powerful and salient negative affects.

Adolescent↗
PubMed1994

Nursing implications of the intracarotid amobarbital procedure.

The intracarotid amobarbital procedure, by inactivation of each hemisphere, provides the opportunity to evaluate language and memory function of the individual considering epilepsy surgery. Careful explanation of this procedure, and its importance to the proposed surgery are vital to the patient's cooperation and performance during this examination. The neuroscience nurse has a significant role in the success of this procedure. Nursing interventions include patient education, monitoring for potential complications, providing comfort measures, and assisting in the management of any life-threatening complications which do develop. A relatively little-known procedure outside of comprehensive epilepsy centers, the IAP offers opportunities for nursing research. These queries include investigation of emotional reactions in relation to gender differences, cultural and educational factors which may effect stimulus selection (eg, bilingual patients) and patient performance.

Amobarbital↗
PubMed1994

Paraneoplastic temporal lobe epilepsy with testicular neoplasm and atypical amnesia.

We report a patient who, at age 38, presented with temporal lobe seizures and an atypical memory disorder 3 years before the discovery of a testicular tumor. Detailed neuropsychological testing revealed a relatively isolated amnestic syndrome. The amnesia was atypical as the patient could retain information for hour-long periods, only to lose it later. Serologic studies revealed the presence of a circulating autoantibody that demonstrated an unusual affinity for the nucleolus of cerebral cortical neurons. Western blot analysis of cortical neurons revealed that this antibody reacted with proteins different from other previously identified paraneoplastic neurologic antigens (Hu, Yo, Ri). We believe this to be a case of paraneoplastic limbic encephalitis secondary to the testicular tumor. This patient presents unique characteristics with respect to the mode of presentation, features of the amnesia, and the presence of a circulating antibody with an unusual reactivity pattern.

Amnesia↗
PubMed1993

The association of multiple personality and temporolimbic epilepsy. Intracarotid amobarbital test observations.

OBJECTIVE: What is the relationship of "multiple personality disorder" in patients with temporolimbic epilepsy to certain types of hemispheric interaction? DESIGN: Case series. SETTING: Tertiary care referral center. PATIENTS: Two patients with temporolimbic epilepsy considered to be surgical candidates referred for the intracarotid amobarbital sodium procedure (IAP). Each individual had presented with different "personalities" in a characteristic temporal relationship to their seizures. INTERVENTIONS: Intracarotid amobarbital sodium procedure, Wada test, and electroencephalogram. MAIN OUTCOME MEASURES: Behavioral observations made during the performance of the IAP. RESULTS: During the IAP, each patient's peri-ictal "personality" changes were precisely replicated. No seizure activity was noted during the IAPs. CONCLUSIONS: These observations suggest that the association of multiple personality and temporolimbic epilepsy is not dependent on seizure discharges per se, but rather may be related to certain types of hemispheric interaction.

Adolescent↗
PubMed1991

Right hemisphere advantage for evaluating emotional facial expressions.

The ability to evaluate the intensity of emotional facial expressions was investigated in patients undergoing the intracarotid sodium amytal procedure. It was found that when the hemisphere non-dominant for language (usually right) was anesthetized, the patients' ratings of the intensity of emotional expressions in photographs were lower than baseline ratings of these expressions. Such an effect was not seen with anesthetization of the hemisphere dominant for language (usually left). Ratings of shades of gray (which served as control stimuli) showed no such effect. The findings are interpreted in terms of a right hemisphere superiority in the perception and evaluation of emotional expression.

Adolescent↗