Properties of spike train spectra in two parietal reach areas.

In the lateral intraparietal area (LIP), a saccade-related region of the posterior parietal cortex (PPC), spiking activity recorded during the memory period of an instructed-delay task exhibits temporal structure that is spatially tuned. These results provide evidence for the existence of 'dynamic memory fields' which can be read-out by other brain areas, along with information contained in the mean firing rate, to give the direction of a planned movement. We looked for evidence of dynamic memory fields in spiking activity in two parietal reach areas, the parietal reach region (PRR) and area 5. Monkeys made center-out reaches to eight target locations in an instructed-delay task with a memory component. Neurons in both areas exhibited sustained activity during the delay period that was spatially tuned. Many single cell PRR spectra exhibited spatially tuned temporal structure, as evidenced by a significant and spatially tuned peak in the 20-50 Hz band. The PRR population spectrum of spike trains was also tuned, with the peak power centered on approximately 25 Hz. In contrast, area 5 spiking activity did not exhibit any significant temporal structure. These results suggest that different mechanisms underlie sustained delay period activity in these two areas and that dynamic memory fields, as revealed by our techniques, are more prominent in PRR than in area 5. Temporal structure in the spike train and local field potential (LFP) are related in at least one other brain area (LIP). The present results suggest then that LFP activity obtained from PRR may be better suited than area 5 LFP activity for use in neural prosthetic systems that incorporate analysis of temporal structure as part of a decode mechanism for extracting intended movement goals.

Sampling properties of the spectrum and coherency of sequences of action potentials.

The spectrum and coherency are useful quantities for characterizing the temporal correlations and functional relations within and between point processes. This article begins with a review of these quantities, their interpretation, and how they may be estimated. A discussion of how to assess the statistical significance of features in these measures is included. In addition, new work is presented that builds on the framework established in the review section. This work investigates how the estimates and their error bars are modified by finite sample sizes. Finite sample corrections are derived based on a doubly stochastic inhomogeneous Poisson process model in which the rate functions are drawn from a low-variance gaussian process. It is found that in contrast to continuous processes, the variance of the estimators cannot be reduced by smoothing beyond a scale set by the number of point events in the interval. Alternatively, the degrees of freedom of the estimators can be thought of as bounded from above by the expected number of point events in the interval. Further new work describing and illustrating a method for detecting the presence of a line in a point process spectrum is also presented, corresponding to the detection of a periodic modulation of the underlying rate. This work demonstrates that a known statistical test, applicable to continuous processes, applies with little modification to point process spectra and is of utility in studying a point process driven by a continuous stimulus. Although the material discussed is of general applicability to point processes, attention will be confined to sequences of neuronal action potentials (spike trains), the motivation for this work.

Can atomic force microscopy achieve atomic resolution in contact mode?

Atomic force microscopy operating in the contact mode is studied using total-energy pseudopotential calculations. It is shown that, in the case of a diamond tip and a diamond surface, it is possible for a tip terminated by a single atom to sustain forces in excess of 30 nN. It is also shown that imaging at atomic resolution may be limited by blunting of the tip during lateral scanning.

Patient outcome alone does not justify the centralisation of vascular services.

BACKGROUND: The Provision of Vascular Services document from the Vascular Surgical Society of Great Britain and Ireland argues for the centralisation of vascular services into units served by a minimum of four vascular consultants. The rationale for this is the presumed advantages of improved patient care, better utilisation of resources and a more comprehensive arrangement of consultant vascular cover. Since April 1998, the Royal Surrey County Hospital (RSCH) has had a single-handed vascular consultant with out-of-hours cross-district consultant vascular cover. OBJECTIVES: To use P-POSSUM analysis to determine patient outcome from the RSCH vascular unit, and to compare these with previously published P-POSSUM analysis from a major vascular unit in Leeds. PATIENTS AND METHODS: All patients undergoing major vascular surgery or amputation between April and November 1998 were analysed. RESULTS: 86 patients underwent 102 surgical procedures in 92 separate admissions. Data retrieval was 100%. Predicted (E) mortality 16 cases; observed (O) mortality 13 cases; O:E ratio 0.80. Predicted morbidity 26 cases; observed morbidity 19; O:E ratio 0.73. O:E ratio for mortality from Leeds = 0.83. CONCLUSIONS: Patient outcome in a single-handed vascular unit, with cross-district consultant cover, is equivalent to that found in a major vascular unit. Centralisation of vascular services cannot be justified on the basis of differences in patient outcome.

Low-dose atropine in electroconvulsive therapy.

Anticholinergic medications such as atropine or glycopyrrolate have long been used in electroconvulsive therapy (ECT) to eliminate parasympathetically mediated dysrhythmias. However, such agents increase heart rate and myocardial workload and may increase risk of cardiac adverse events. What is needed is an intervention that is parasympatholytic without substantially increasing myocardial workload. In this study, a low dose of atropine was compared with placebo in ECT with attention to heart rate, blood pressure, cardiac rhythm, myocardial workload, and parasympathetic function. The dose of atropine that was used effectively blocked vagal tone with only a small and probably not clinically significant rise in myocardial workload for only a few minutes after the ECT seizure.

Ketamine anesthesia in electroconvulsive therapy.

The use of ketamine anesthesia in electroconvulsive therapy (ECT) has been limited by its effects on blood pressure and concerns about untoward psychological reactions. However, because its effect on seizures is presumably less than that of methohexital, ketamine is listed as an alternative method to prolong seizure length. In this case series, 10 patients were given ketamine anesthesia during ECT. Whereas blood pressures were elevated above those seen with methohexital, seizure lengths actually decreased nonsignificantly with ketamine. There were no adverse psychological reactions noted with ketamine, which was generally well tolerated. It is concluded that ketamine anesthesia with the doses used in this series is unlikely to be associated with longer seizures in ECT. However, for theoretical reasons discussed, ketamine may be worth studying further in ECT.

Possible impact of stimulus duration on seizure threshold in ECT.

Seizure thresholds were measured in patients treated with right unilateral electroconvulsive therapy (ECT) using 0.9 amp, 0.5 ms constant current pulses at 30 Hz for 0.93-2.8 s. Using these parameters, only two patients failed to seize at stimulus charges < or = 75.6 mC. Three patients were excluded from further analysis because they experienced generalized motor or electrographic seizures lasting less than 25 s and 30 s, respectively. The remaining 52 patients had a mean seizure threshold of 48.9 +/- 15.3 mC. Seizure threshold was correlated with age, but not sex. These values for seizure threshold are significantly lower than those reported previously using longer pulse-briefer train duration stimuli, suggesting that characteristics of the electrical stimulus influence seizure threshold. These findings have implications for electrical dosing in right unilateral ECT.

Mianserin-induced up-regulation of serotonin receptors on normal human platelets in vivo.

The antidepressant, mianserin, is a serotonin receptor (5-HT2) antagonist and produces down-regulation of 5-HT2 and 5-HT1c receptors in the cerebral cortex of rats. In preparation for testing the validity of platelets as a model system for changes in 5-HT2 receptors during antidepressant drug treatment, mianserin (40 mg daily), was given to five human volunteers for five days, and platelets were collected on days 0, 1, 6, and 8. 5-HT2 receptor affinity and density were measured by specific binding of 125I-LSD, with and without an excess of spiperone. 5-HT uptake site affinity and density were determined by 3H-paroxetine binding, with and without an excess of fluoxetine. Platelet serotonin content was measured using high pressure liquid chromatography and electrochemical detention. Platelet 5-HT2 receptor density was increased and the ligand affinity was decreased during mianserin administration. In contrast, platelet 5-HT content was not altered significantly by mianserin administration, nor was platelet uptake site density and ligand affinity.

Binding of transition metals by apolipoprotein A-I-containing plasma lipoproteins: inhibition of oxidation of low density lipoproteins.

We have found transition metals tightly bound to apolipoprotein A-I-containing lipoproteins [Lp(A-I)] isolated by selected affinity immunosorption from human serum. Prominent among the metal ions detected were iron and copper. By immunoblotting the proteins of Lp(A-I), we detected both transferrin and ceruloplasmin. The transferrin-containing Lp(A-I) particles, isolated by selected affinity immunosorption against transferrin, were larger (mean diameter of 14.2 nm) and had a higher protein content than most high density lipoproteins (HDL). Ultracentrifugally isolated HDL were found to contain much less transferrin, whereas transferrin was found associated with apolipoprotein A-I from the greater than 1.21-g/ml ultracentrifugal fraction. This suggests that the complex is not recovered in the classic HDL density interval because of its very high density. HDL inhibit copper-catalyzed oxidation of low density lipoproteins (LDL) in vitro. We have found that immunoisolated Lp(A-I) are an order of magnitude more effective in inhibiting the oxidation of LDL than ultracentrifugally isolated HDL, on the basis of protein mass. When the Lp(A-I) particles containing transferrin and ceruloplasmin were removed from the bulk of Lp(A-I), inhibition of the in vitro oxidation of LDL was significantly decreased.

ECT-induced interictal delirium in patients with a history of a CVA.

Earlier works have documented a high incidence of affective disorders in patients with a history of a cerebrovascular accident (CVA). In general, electroconvulsive therapy (ECT) has been reported to be effective in treating depressed patients with a history of CVA. Recent works have shown that preexisting structural brain changes may predispose patients to develop interictal ECT-induced delirium. However, the incidence of ECT-induced interictal delirium in patients with a history of CVA has not been directly studied. In this pilot study, the authors examined the incidence of ECT-induced interictal delirium in 14 depressed CVA patients compared with 14 elderly depressed controls (without a history of CVA). Interestingly, the overall incidence of delirium was identical in both groups (28.5%). However, consistent with previous works, some patients who had had a recent CVA involving the caudate nucleus appeared more likely to develop delirium. Thirteen of the 14 depressed CVA patients (92%) showed a moderate to significant improvement in their depressive symptoms from ECT. None of the patients developed significant cardiac complications during ECT.

Simultaneous major depression and panic disorder: treatment with electroconvulsive therapy.

BACKGROUND: Major depression and panic disorder commonly occur together. Patients with simultaneous depression and panic disorder may have a higher lifetime rate of suicide attempts and an overall worse prognosis than patients with either depression or panic disorder alone. In addition, preliminary work suggests that some of these patients may not respond satisfactorily to antidepressants. In this report, we describe the clinical courses of eight consecutive patients with simultaneous major depression and panic disorder who were referred for ECT at our institution. METHOD: Eight consecutive patients who met DSM-III-R criteria for simultaneous major depression and panic disorder received ECT. All eight patients were evaluated by a structured clinical interview and the patients' major depression and panic disorder were evaluated with a 7-point Clinical Global Impressions severity rating scale. RESULTS: Before ECT was begun, each subject's panic disorder and depression were rated as at least markedly ill. After receiving ECT, all eight showed improvement in their depression. In addition, none of the eight patients reported having a panic attack from the time of their fourth ECT treatment until discharge. CONCLUSION: In this report, eight consecutive patients with simultaneous major depression and panic disorder improved with ECT. Further work is required which examines the potential utility of ECT in treating these patients.

Clinical pharmacokinetics of tricyclic antidepressant overdose.

Tricyclic antidepressants (TCAs) taken in large quantities during suicide attempts have altered pharmacokinetics. Their absorption may be delayed by inhibition of gastric emptying and peristalsis. A significant enterohepatic recirculation delays final elimination of a large fraction of the drug. The enzymes responsible for TCA benzyl-hydroxylation can become saturated and thus reduce TCA elimination to zero-order kinetics. TCA unbound to plasma proteins may also increase because of an acidemia resulting from a respiratory depression after overdose. Other compounds are ingested in suicide attempts which greatly change TCA pharmacokinetics. Metabolism of ethanol generates an excess of reducing equivalents which inhibit TCA oxidative metabolism. Neuroleptics directly inhibit TCA hydroxylation. Fluoxetine significantly prolongs elimination and increases plasma levels of TCA. Toxic hepatic metabolites of acetaminophen would delay TCA elimination. The elderly have slower rates of drug elimination and are particularly susceptible to TCA antidepressants taken in overdose.

ECT-induced delirium in depressed patients with Parkinson's disease.

In this pilot study, a prolonged (interictal) delirium was induced by electroconvulsive therapy (ECT) in seven out of seven depressed patients with Parkinson's disease. This occurrence of delirium appears much higher than what has been reported in other patient populations. These findings are consistent with several lines of data that have implicated the basal ganglia in the development of delirium from other causes, and they suggest that structural changes in these areas may predispose individuals to develop an interictal delirium during a course of ECT.

Acute psychosis in a patient with Epstein-Barr virus infection.

A case study is presented of an adolescent female who became psychotic and attempted suicide during an acute Epstein-Barr Virus infection. Resolution of the infection resulted in the patient returning to her previous normal mental status. The adolescent's ingestion of acetaminophen masked the signs and symptoms of infection and delayed proper diagnosis.