Perceptual switch rates with ambiguous structure-from-motion figures in bipolar disorder.

Slowing of the rate at which a rivalrous percept switches from one configuration to another has been suggested as a potential trait marker for bipolar disorder. We measured perceptual alternations for a bistable, rotating, structure-from-motion cylinder in bipolar and control participants. In a control task, binocular depth rendered the direction of cylinder rotation unambiguous to monitor participants' performance and attention during the experimental task. A particular direction of rotation was perceptually stable, on average, for 33.5s in participants without psychiatric diagnosis. Euthymic, bipolar participants showed a slightly slower rate of switching between the two percepts (percept duration 42.3s). Under a parametric analysis of the best-fitting model for individual participants, this difference was statistically significant. However, the variability within groups was high, so this difference in average switch rates was not big enough to serve as a trait marker for bipolar disorder. We also found that low-level visual capacities, such as stereo threshold, influence perceptual switch rates. We suggest that there is no single brain location responsible for perceptual switching in all different ambiguous figures and that perceptual switching is generated by the actions of local cortical circuitry.

Sustained attention-deficit confirmed in euthymic bipolar disorder but not in first-degree relatives of bipolar patients or euthymic unipolar depression.

BACKGROUND: Cognitive dysfunction persists in the euthymic phase of bipolar disorder and may provide a marker of underlying neuropathology and disease vulnerability. This study aimed to replicate a deficit in sustained attention in euthymic bipolar patients and investigate sustained attention in first-degree relatives of bipolar probands and in remitted patients with major depressive disorder. METHODS: The rapid visual information processing (RVIP) task was used to measure sustained attention in 15 euthymic patients with bipolar disorder and 15 control subjects in experiment 1 and in 27 first-degree relatives of bipolar probands, 15 remitted patients with major depressive disorder, and 46 control subjects in experiment 2. RESULTS: Sustained attention deficit was confirmed in the euthymic bipolar patients in experiment 1, but the deficit was not statistically significant in remitted major depressed patients or in the relatives of bipolar probands. CONCLUSIONS: A deficit of sustained attention is not present in patients with recurrent major depression tested during remission nor is it discriminable in the first-degree relatives of bipolar probands. Thus, the confirmed abnormality in euthymic bipolar patients may be acquired as a consequence of bipolar illness. However, future studies of relatives will require larger sample sizes to exclude or utilize small genetic effects.

Sleep-related functioning in euthymic patients with bipolar disorder, patients with insomnia, and subjects without sleep problems.

OBJECTIVE: The authors investigated sleep-related functioning in euthymic patients with bipolar disorder. METHOD: Euthymic patients with bipolar disorder (N=20), patients with insomnia (N=20), and subjects with good sleep (N=20) were compared on data from interviews and questionnaires and on findings from eight consecutive days and nights of sleep diary keeping (subjective sleep estimate) and actigraphy (objective sleep estimate). RESULTS: Seventy percent of the euthymic patients with bipolar disorder exhibited a clinically significant sleep disturbance. Compared with the other groups, the bipolar disorder group exhibited impaired sleep efficiency, higher levels of anxiety and fear about poor sleep, lower daytime activity levels, and a tendency to misperceive sleep. The bipolar disorder group held a level of dysfunctional beliefs about sleep that was comparable to that in the insomnia group and significantly higher than that in the good sleeper group. CONCLUSIONS: Insomnia is a significant problem among euthymic patients with bipolar disorder. Components of cognitive behavior therapy for insomnia, especially stimulus control and cognitive therapy, may be a helpful adjunct to treatment for patients with bipolar disorder.

A dose-finding study on the effects of branch chain amino acids on surrogate markers of brain dopamine function.

RATIONALE: We have previously shown in healthy volunteers that an amino acid mixture lacking tyrosine and phenylalanine reduces tyrosine availability to the brain and produces cognitive and neuroendocrine effects consistent with reduced dopamine function. This could provide a potential nutritional approach to disorders such as mania and schizophrenia, which are characterised by overactivity of dopamine pathways. The amino acid mixture we tested previously is unpalatable, whereas mixtures containing only branch chain amino acids can be made more palatable. However, the effects of such mixtures on dopamine function in humans have not been studied. OBJECTIVE: To assess the tolerability of different doses of branch chain amino acids and to measure their effects on neuroendocrine and cognitive measures sensitive to changes in dopamine function. METHODS: We used a randomised, double-blind, cross-over design in 12 healthy volunteers to assess the effect of single oral doses of 10 g, 30 g and 60 g branch chain amino acids on plasma prolactin and a test of spatial recognition memory RESULTS: The branch chain amino acids were well tolerated. The availability of tyrosine for brain catecholamine synthesis decreased in a dose-related manner. As hypothesised, the drink increased both the plasma prolactin and the latency to respond on the spatial recognition memory task. CONCLUSIONS: A drink containing branch chain amino acids is well tolerated in healthy volunteers and produces effects consistent with lowered dopamine function.