Neurophysiological correlates of error correction in sensorimotor-synchronization

In a sensorimotor synchronization task requiring subjects to tap in synchrony with an auditory stimulus, occasional perturbations (i.e., interval changes) in an otherwise isochronous sequence of auditory metronome stimuli are known to be compensated remarkably swift and with surprising precision, even when they are too small to be consciously perceived. To investigate the neural substrate and the informational basis of error correction in sensorimotor synchronization, we recorded movement-related, auditory-evoked, and error-related EEG potentials. Experiment 1 confirmed rapid adjustment to stimulus phase shifts, with faster correction of large (50 ms) compared to small (15 ms) shifts. In addition to being corrected faster, there was overcorrection of the 50 ms shifts, attributed to engagement of period correction mechanisms. For +50 ms shifts, a neural correlate of period correction was identified in the form of medial frontal cortex activation, preceded by an error-related brain potential (ERN). Auditory-evoked potential (AEP) amplitudes were sensitive to stimulus phase shifts of both large and small magnitude. Further experiments with a smaller magnitude 10 ms phase shift (Experiment 2) and passive auditory stimulation (Experiment 3) provided evidence that the modulation of AEP amplitudes is not due to metronome interval changes, but may represent auditory-somatosensory activation. Together, behavioral and neurophysiological data support the hypothesis that phase correction is a largely automatic process, not dependent on conscious perception of changes in timing. By contrast, perceivable phase shifts may invoke timekeeper adjustments accompanied by medial frontal cortex activity.

Clinical and methodological factors related to reliability of the best-estimate diagnostic procedure

OBJECTIVE

The reliability and accuracy of the best-estimate diagnostic procedure were examined, and factors associated with reliability were determined.

METHOD

The subjects were 134 members of large multigenerational pedigrees densely affected by bipolar disorders or schizophrenia. Three best-estimate diagnoses were derived: first, by a research psychiatrist and research assistant unblind to the relatives' diagnoses; second, by two blind independent psychiatrists; third, by a panel of four blind psychiatrists. The subjects were characterized on several clinical and methodological variables, which were used to compare the agreements of two types of best-estimate diagnoses with the disagreements.

RESULTS

There was satisfactory agreement between the unblind and blind consensus best-estimate diagnoses and between the two blind independent psychiatrists. Latent class analyses revealed that limited sensitivity was the main source of imperfect reliability. Confusability analyses revealed that the most problematic diagnostic distinctions involved schizoaffective disorder, which was confused with schizophrenia, bipolar I disorder, and schizophreniform disorder. Blindness significantly affected diagnostic outcome in latent class analyses. Moreover, for diagnostic disagreements, unblind diagnoses had greater continuity with the most predominant diagnosis in the pedigree than did blind diagnoses. Diagnostic disagreements were associated with the presence of mixed affective and psychotic symptoms, less diagnostic certainty, and shorter duration of illness.

CONCLUSIONS

These results suggest that it is possible to identify cases that are more likely to lead to diagnostic disagreements in family and epidemiological studies and that blind diagnoses may help to prevent false positive diagnoses, which may be particularly detrimental to genetic linkage analyses.

6p24-22 region and major psychoses in the Eastern Quebec population. Le Groupe IREP

Recent reports of a linkage trend in 6p24-22 for schizophrenia (SZ), in different samples, were tempered by the concurrent evidence of negative reports in other samples. In the studies showing positive results, different definitions of affection and a wide spectrum of diagnoses were used. Our objectives were not only to test for linkage at 6p24-22 in the Eastern Quebec population, but also to test whether this putative vulnerability locus was either selectively linked to schizophrenia (SZ), or to bipolar disorder (BP), or to both major psychoses. Parametric and nonparametric linkage analyses with 12 microsatellite markers in 6p24-p22 were performed on a sample of 18 large multigenerational pedigrees (N = 354) either affected by SZ, or by BP, or equally affected by both major psychoses (i.e., mixed pedigrees). Three affection definitions were usually tested in our program: one on schizophrenia (SZ), one on bipolar disorder (BP), and one that comprised SZ and BP under the hypothesis of a susceptibility locus common to both in major psychoses (common locus, CL). The results of parametric analyses did not support a major gene hypothesis. However, in one large mixed pedigree (#151), we observed with the common locus phenotype (CL) lod scores of 2.49 and 2.15, respectively, at the D6S296 and D6S277 loci under a dominant model. Our data suggest the presence of a potential vulnerability locus at 6p24-22 that could be related to both schizophrenia and bipolar affective disorder. These results may be seen as congruent with former studies that used schizoaffective as well as schizophrenia diagnoses as entry criteria for the affected families, and used an affection definition that comprised affective psychoses as well as schizophrenia.

[Diabetic nephropathy]

Diabetic nephropathy morbidity and mortality rates are high for both Type I and Type II diabetes. The various stages of diabetic nephropathy have been well documented for Type I diabetes, but not for Type II. We examine the natural history of this problem and recommended treatments, with emphasis on the characteristics of each type.