A method for finding the inverse of a matrix

The problem of solving simultaneous linear equations is one that frequently confronts the scientist. Whenever it is desired to state the parameters as expressions of the constant terms of these equations, the problem resolves itself into the discovery of the inverse of the matrix of coefficients. The method here described gives a routine for the solution of this problem.     

Television's role regarding alcohol use among teenagers

The purpose of this study was to determine the extent to which adolescents classified as light, moderate, or heavy television viewers differ regarding alcohol use. The extent to which demographic variables mediate the television-alcohol association also was investigated. A total of 394 high school males completed a written questionnaire to assess television and drinking practices. As hypothesized, heavy viewers consumed alcohol significantly more often than did light and moderate viewers, especially the former, particularly when demographic variables were controlled simultaneously. Television as a powerful and pervasive influence on youth, containing many undesirable health messages, is discussed.     

Methylphenidate in hyperactive children: Differential effects of dose on academic,learning, and social behavior

Methylphenidate (Ritalin) has been shown to have differential effects on hyperactive children's behavior as a function of dose level. In the present investigation, a triple-blind, placebo-control, within-subject (crossover) experimental design was employed in which 12 hyperactive boys between 6 and 10 years received three different dosages of methylphenidate (5, 10, and 15 mg) in a randomly assigned sequence. Dosage effects were assessed on clinic(PAL-Paired Associates Learning test) and school-(percent on task, teacher ratings, work completion rates, and accuracy) related behaviors. For 10 of the children, classified as responders to medication by the PAL using the criteria of Swanson, Kinsbourne, and colleagues, a series of ANCOVAs with repeated measures showed significant dosage effects on teacher ratings (p 01), percent on task (p 01), academic accuracy (p 05), and assignment completion rates (p 05). PAL performance was also significantly enhanced (p 01) after optimal dose levels were considered. Subsequent trend analysis showed a significant positive linear relationship between dose and each of the dependent variables. A comparison of fixed-dose and miligram-per-kilogram plots showed that children's performance across the different dosages were clearly individualistic and task-specific, even when similar body weights were compared. The implications of using clinic-based testing to determine optimal medication responsivity were discussed.We would like to express our sincere appreciation to the following pediatricians for their valuable assistance: W. H. McDermott, D. J. Chronley, R. B. Trivett, F. J. Jehle, P. M. Small, and F. T. Leong. Grateful acknowledgement is also extended to the two anonymous reviewers whose comments contributed to the content of this paper, and to the undergraduate and graduate student members of the Children's Learning Clinic.     

Napping promotes inter-session habituation to emotional stimuli

The effects of a daytime nap on inter-session habituation to aversive visual stimuli were investigated. Healthy young adult volunteers viewed repeated presentations of highly negative and emotionally neutral (but equally arousing) International Affective Picture System (IAPS) photographs during two afternoon sessions separated by 2.5h. Half of the photographs were shown at both sessions (Repeated Sets) and half differed between sessions (Novel Sets). For each stimulus presentation, evoked skin conductance response (SCR), heart-rate deceleration (HRD) and corrugator supercilii EMG response (EMG), were computed and range corrected using respective maximum session-1 responses. Following each presentation, subjects rated each photograph on dimensions of pleasantness and arousability. During the inter-session interval, Nap subjects had a 120-min polysomnographically monitored sleep opportunity, whereas Wake subjects watched a non-stimulating video. Nap and Wake subjects did not differ in their subjective ratings of photographs. However, for Repeated-Set photographs, Nap subjects demonstrated greater inter-session habituation in SCR and EMG but a trend toward lesser inter-session habituation in HRD. These group differences were absent for Novel-Set photographs. Group differences across all measures were greater for negative stimuli. Occurrence of SWS during the nap was associated with greater inter-session habituation of EMG whereas occurrence of REM was associated with lesser inter-session habituation of SCR to negative stimuli. Sleep may therefore promote emotional adjustment at the level of somatic responses. Physiological but not subjective inter-session habituation to aversive images was enhanced by a daytime nap.     

Feigning combat-related posttraumatic stress disorder on the personality assessment inventory

This study examined whether individuals who were instructed on the Diagnostic and Statistical Manual of Mental Disorders (4th ed. [DSM-IV]; American Psychiatric Association, 1994) criteria for posttraumatic stress disorder (PTSD) could feign PTSD on the Personality Assessment Inventory (PAI; Morey, 1991). The study also investigated whether PAI indexes of symptom exaggeration, the Negative Impression Management (NIM) scale and the Malingering index, could identify individuals feigning PTSD. The diagnostic rule for PTSD (Morey, 1991, 1996) was applied to the profiles of a group of 23 veterans with combat-related PTSD and 23 male undergraduates instructed to malinger PTSD. Seventy percent of the student malingerers produced profiles that received diagnostic consideration for PTSD. The NIM cutting score (> or = 8) was highly effective in detecting simulation of PTSD but resulted in the misclassification of a large number of true PTSD cases. There were no significant differences in the overall efficiency of the test with various validity criteria. We discuss the implications of these findings for the use of the PAI in the diagnosis of combat-related PTSD.     

The L-Type voltage-gated calcium channel Cav1.3 mediates consolidation, but not extinction, of contextually conditioned fear in mice

Using pharmacological techniques, it has been demonstrated that both consolidation and extinction of Pavlovian fear conditioning are dependent to some extent upon L-type voltage-gated calcium channels (LVGCCs). Although these studies have successfully implicated LVGCCs in Pavlovian fear conditioning, they do not provide information about the specific LVGCC isoform involved. Both of the major LVGCC subtypes found in the brain (Cav1.2 and Cav1.3) are targets of the pharmacological manipulations used in earlier work. In this study, we used mice in which the gene for the pore-forming subunit (alpha1D) Cav1.3 was deleted (Cav1.3 knockout mice) to elucidate its contribution to consolidation and extinction of conditioned fear. We find that Cav1.3 knockout mice exhibit significant impairments in consolidation of contextual fear conditioning. However, once sufficiently overtrained, the Cav1.3 knockout mice exhibit rates of extinction that are identical to that observed in wild-type mice. We also find that Cav1.3 knockout mice perform as well as wild-type mice on the hidden platform version of the Morris water maze, suggesting that the consolidation deficit in conditioned fear observed in the Cav1.3 knockout mice is not likely the result of an inability to encode the context, but may reflect an inability to make the association between the context and the unconditioned stimulus.