Broadening the scope of our understanding of mechanisms: lessons from the history of the morning-after pill

Synthese - Philosophers of science and medicine now aspire to provide useful, socially relevant accounts of mechanism. Existing accounts have forged the path by attending to mechanisms in...     

Component mechanisms underlying the processing of hierarchically organized patterns: inferences from patients with unilateral cortical lesions

Subjects identified target letters that occurred randomly at the local or global level in a divided attention task. The visual angle of the stimuli was varied. Neurologically intact controls showed a reaction time advantage for local targets which increased as visual angle increased. Patients with lesions centered in the posterior superior temporal gyrus (STG) showed a larger local advantage than controls if the lesion was on the right and a global advantage if the lesion was on the left. STG patients were no more influenced by visual angle than were controls. Control subjects also showed the usual interference of global distractors on responding to local targets. STG patients showed little evidence of interference. Control patients with lesions centered in the rostral inferior parietal lobe performed normally. The findings suggest that several component mechanisms are involved in the processing of hierarchical levels of structure, each linked to specific anatomical regions.     

Neural mechanisms underlying the higher levels of subjective well-being in extraverts: Pleasant bias and unpleasant resistance

The present study investigated the neural mechanisms that underlie the higher levels of subjective well-being in extraverts. The impact of extraversion on the human sensitivity to pleasant and unpleasant pictures of diverse emotional intensities was examined. We recorded event-related potentials (ERPs) for highly positive (HP), moderately positive (MP), and neutral stimuli in the pleasant session, and for highly negative (HN), moderately negative (MN), and neutral stimuli in the unpleasant session, while subjects (16 extraverts and 16 ambiverts) performed a standard/deviant categorization task, irrespective of the emotionality of the deviant stimuli. The results showed significant emotion effects for HP and MP stimuli at the P2 and P3 components in extraverts, but not in ambiverts. Despite a pronounced emotion effect for HN stimuli across the P2, N2, and P3 components in both samples, ambiverts displayed a significant emotion effect for MN stimuli at the N2 and P3 components that was absent in extraverts. The posterior cingulate cortices, which connect multiple neural regions that are important in interactions of emotion and extraversion, may mediate the extravert-specific emotion effect for pleasant stimuli. Thus, extraverts are less susceptible to unpleasant stimuli of mild intensity than are ambiverts, while extraverts have an additional enhanced sensitivity to pleasant stimuli, regardless of emotion intensity. Consequently, the decreased threshold for pleasant emotion and the increased threshold for unpleasant emotion might be essential neural mechanisms that underlie the higher levels of subjective well-being in extraverts.     

Depression in early adolescence: Contributions from relational aggression and variation in the oxytocin receptor gene

Interpersonal stress arising from relational aggression (RA)—the intentional effort to harm others via rejection and exclusion—may increase risk for depression in youth. Biological vulnerabilities related to the hormone oxytocin, which affects social behavior and stress responses, may exacerbate this risk. In a community sample of 307 youth (52% female; age range = 10–14 years), we tested whether (1) the association between RA and subsequent depressive symptoms was mediated through social problems and (2) a single nucleotide polymorphism (rs53576) in the oxytocin receptor gene (OXTR) moderated this indirect association between RA and depression, where GG homozygotes are predicted to be more sensitive to the effects of social problems than A‐allele carriers. Youth‐reported RA and depressive symptoms were measured using a structured interview and a questionnaire, respectively. DNA was extracted from saliva collected with Oragene kits. Consistent with the interpersonal theory of depression, the association between relational aggression and subsequent depressive symptoms was mediated by social problems. This indirect effect was further moderated by rs53576 genotype, such that GG homozygotes showed a stronger mediation effect than A‐carriers. These results suggest that rs53576 variants confer vulnerability for depression within the context of interpersonal risk factors, such that youth with the GG genotype may be particularly sensitive to the social consequences resulting from RA.

     

The negative consequences of threat: a functional magnetic resonance imaging investigation of the neural mechanisms underlying women's underperformance in math

This study used functional magnetic resonance imaging to identify the neural structures associated with women's underperformance on math tasks. Although women in a control condition recruited neural networks that are associated with mathematical learning (i.e., angular gyrus, left parietal and prefrontal cortex), women who were reminded of gender stereotypes about math ability did not recruit these regions, and instead revealed heightened activation in a neural region associated with social and emotional processing (ventral anterior cingulate cortex).     

Getting the ethics right regarding research in the emergency setting: lessons from the PolyHeme study

Research in emergency settings (RES) has become a major public issue with urgent policy implications. Significant attention has focused recently on RES in response to the trial of PolyHeme, a synthetic blood substitute, in trauma victims in hemorrhagic shock. Unfortunately, the discussion of the PolyHeme trial in the popular and scholarly press leaves important questions unanswered. This paper articulates three important lessons from the PolyHeme trial that have significant policy implications. First, the RES regulations should be re-visited, particularly the requirement that existing treatments be unproven or unsatisfactory in order for research to be acceptable without consent. Second, further conceptual and empirical scholarship is needed to accomplish the goal of effectively involving communities. Third, a more subtle analysis is needed regarding how to balance the needs of maintaining public trust and protecting confidential trade information in the context of RES.     

Pathways from marital aggression to infant emotion regulation: the development of withdrawal in infancy

Associations between marital conflict and infant emotion regulation exist, but explanatory pathways have not been explored. For older children, parental behavior partially mediates this association through a "spillover" process. We test: associations between mothers' and fathers' verbally aggressive marital conflict, infant temperament, and infant withdrawal; mediating effects of negative maternal behavior, and moderating effects of infant temperament, exposure to marital arguments, and contact with father. Eighty mothers, 73 fathers, and their 6-month-old infants participated; parents reported marital aggression prenatally, mothers reported infant exposure to arguments, direct caregiving by father, and infant temperament at 5 months. Negative maternal behavior, infant withdrawal, distress to novelty, activity, and look away were observed at 6 months. Mothers' and fathers' aggressive marital conflict predicted infant withdrawal, interactively with exposure to marital arguments and extent of father caregiving, as did infant temperament and negative maternal behavior. Maternal behavior did not mediate between marital conflict and withdrawal.     

New lessons from knockout mice: The role of serotonin during development and its possible contribution to the origins of neuropsychiatric disorders

Serotonin (5-HT) modulates numerous processes in the central nervous system that are relevant to neuropsychiatric function and dysfunction. It exerts significant effects on anxiety, mood, impulsivity, sleep, ingestive behavior, reward systems, and psychosis. Serotonergic dysfunction has been implicated in several psychiatric conditions but efforts to more clearly understand the mechanisms of this influence have been hampered by the complexity of this system at the receptor level. There are at least 14 distinct receptors that mediate the effects of 5-HT as well as several enzymes that control its synthesis and metabolism. Pharmacologic agents that target specific receptors have provided clues regarding the function of these receptors in the human brain. 5-HT is also an important modulator of neural development and several groups have employed a genetic strategy relevant to behavior. Several inactivation mutations of specific 5-HT receptors have been generated producing interesting behavioral phenotypes related to anxiety, depression, drug abuse, psychosis, and cognition. In many cases, knockout mice have been used to confirm what has already been suspected based on pharmacologic studies. In other instances, mutations have demonstrated new functions of serotonergic genes in development and behavior.     

Oscillator mechanisms in the human motor system: investigating their properties using the aftercontraction effect

It is proposed that the human motor system is organized to use hardware and/or software non-linear oscillator mechanisms, the output of these oscillators being responsible for driving the limbs via signals to muscle groups. Following earlier theoretical development, it is argued that these muscle groupings act as a unit and themselves are likely to behave as a non-linear system. The attributes of non-linear oscillators are many, and they are potentially significant for the explanation of motor behavior. This paper reviews and presents recent experiments that investigated the properties of muscular aftercontraction. The basic finding shows that subsequent to a period of moderate strain against a fixed surface the treated limb exhibits prolonged involuntary molar oscillations in the plane of the treatment. These results provide for the presence of driving oscillator mechanisms in the human motor apparatus. The mechanisms show generality of action in that directed attention can lead to oscillation of untreated limbs. Overall, the experiments showed that the movements exhibited the mutual interaction, synchronization, and preservation of phase relationships that are fundamental properties of non-linear oscillators. the picture that emerges is that these mechanisms can drive involuntary movements that are richly patterned: like slow versions of voluntary movements. The aftercontraction phenomenon proves to be an excellent tool for research on the oscillatory substrate of human motor organization.     

Change and continuity in neurobehavioral development: lessons from the study of neurobiology and neural plasticity

The goal of this paper is to discuss our current understanding of change and continuity in neurobehavioral development. After describing the basic elements of neurobiological development, attention is focused on the myriad of ways experience influences the developing and developed brain. This literature is used to illustrate the complexity of both brain and behavioral development in the context of change and continuity. The implications of considering brain/behavior relations in the context of development comprise the final section of the paper.     

Stabilized images: Functional relationships among populations of orientation-specific mechanisms in the human visual system

Two experiments are presented in which fading rates of stabilized line stimuli were measured following prolonged adaptation to nonstabilized grating patterns in various orientations. Results indicated that some orientation-specific effects are sensitive to small variations of orientation around an optimal orientation, as well as to stimuli rotated 90 deg from the optimal orientation. These data were interpreted in terms of interactions among populations of orientation-specific mechanisms in the human visual system.     

Extracellular amino acid levels in the paraventricular nucleus and the central amygdala in high- and low-anxiety dams rats during maternal aggression: regulation by oxytocin

Brain oxytocin (OT) regulates aspects of emotionality and stress coping including maternal behavior and maternal aggression. Maternal aggression correlates with the amount of OT released within the paraventricular nucleus (PVN) and the central amygdala (CeA). OT, a key neurotransmitter or neuromodulator, is likely to modulate other neurotransmitter systems. Here, we investigated the dynamic changes in extracellular concentrations of the amino acids aspartate, glutamate, gamma-aminobutyric acid (GABA), serine, histidine, arginine and taurine in the PVN and CeA in lactating rats bred for high (HAB) and low (LAB) anxiety-related behavior under basal conditions and during maternal aggression. Further, to determine whether local OT is involved in the regulation of amino acid release we infused a selective OT receptor antagonist (OTA) via local retrodialysis. Within the CeA, HAB and LAB dams differed in the basal release of glutamate and arginine. Infusion of a selective OTA increased the concentrations of glutamate and aspartate in LAB dams and GABA in HAB dams. In OTA-treated HAB and LAB dams taurine levels increased during maternal aggression. Within the PVN, the highly-aggressive HAB dams showed a more pronounced increase in aspartate and serine levels; the latter being attenuated by local OTA administration. However, OTA did not affect the level of any amino acid in the LAB dams. Thus, the extracellular concentrations of selected amino acids differed between lactating HAB and LAB dams under both basal conditions and following maternal aggression. The effects of OT within the CeA and PVN on maternal aggressive behavior might be related to its regulation of local amino acid release.     

Exploring the forgetting mechanisms in working memory: Evidence from a reasoning span test

In working memory (WM) span tests participants have to maintain to-be-remembered information while processing other, potentially distracting, information. Previous studies have shown that WM span scores are greater when span lists start with a long processing task and end with a short processing task than when these processing tasks are presented in the reverse order (e.g., Towse, Hitch, & Hutton, 2000). In Experiment 1, we obtained a similar stimulus order effect in a reasoning span test, using reasoning sentences that were equated for length in terms of the number of constituent words, but which differed in processing complexity; span scores were greater when lists began with a complex sentence and ended with a simple sentence than when this stimulus order was reversed. In Experiment 2, the stimulus order effect was not found when processing duration was held constant while sentence complexity was varied using a computer-paced moving window presentation paradigm. These results suggest that duration-based constraints can affect degree of forgetting independently of the load generated during processing phases in WM span performance and therefore imply that time-related forgetting can occur in WM span tests, particularly when the difficulty of the processing component blocks active maintenance of to-be-remembered material.     

Adolescents' peer orientation: changes in the support system during the past three decades

Identical questionnaires were administered to samples of high school students (N = 570) in 1963, 1976, and 1982. The purpose was to determine to what extent they relied on their peers on a number of important issues. The findings revealed no monolithic orientation, but showed that the nature of the issue determines which reference group is activated: peers or parents. While educational, career, and financial concerns are more parent oriented, almost all social activities are peer oriented. However, the strength of the orientation has been fluctuating over the past decades: the teenagers showed lowest peer orientation in 1963, highest in 1976, and intermediate in 1982.     

Engaging African American men in empirically based marriage enrichment programs: lessons from two focus groups on the ProSAAM project

To better meet the needs of eligible African American men who were reluctant to enroll in a 5-year study called the Program for Strong African American Marriages (ProSAAM), we employed two focus groups to listen to the voices of a sample of the population being recruited and to explore their feedback about taking part in such a marriage enrichment program and how best to recruit other African American men. We explain our application of the focus group results to our recruitment of African American married couples for ProSAAM. The positive outcomes from the implementation of these results can provide potential ideas for those seeking innovative means to improve recruitment of African American men to programs that strengthen marital relationships.     

Flow experience in physical activity: Examination of the internal structure of flow from a process-related perspective

Considering the phenomenology of flow experience reflects attentional processes, Nakamura and Csikszentmihalyi (Handbook of positive psychology, Oxford University Press, New York, 2002) classified the components of flow experience into proximal conditions and the characteristics of a subjective state while being in flow. The present study was conducted to clarify the concept of flow through examination of the interrelationships among the components from a process-related perspective. A total of 1,048 participants completed the Japanese versions of the Flow State Scale-2 (Kawabata et al. in Psychol Sport Exerc 9:465–485, 2008), and based on their scores, 591 respondents were considered to be in a flow state during their physical activity. A proposed higher-order confirmatory factor model and a full structural equation model were tested for the flow respondents. The results of the higher-order model indicated that the 9 flow factors were empirically classified into the flow state and its proximal condition. Furthermore, the outcomes of the full structural model preliminarily supported the hypothesized sequential relationships among flow factors.     

How memory mechanisms are a key component in the guidance of our eye movements: Evidence from the global effect

Investigating eye movements has been a promising approach to uncover the role of visual working memory in early attentional processes. Prior research has already demonstrated that eye movements in search tasks are more easily drawn toward stimuli that show similarities to working memory content, as compared with neutral stimuli. Previous saccade tasks, however, have always required a selection process, thereby automatically recruiting working memory. The present study was an attempt to confirm the role of working memory in oculomotor selection in an unbiased saccade task that rendered memory mechanisms irrelevant. Participants executed a saccade in a display with two elements, without any instruction to aim for one particular element. The results show that when two objects appear simultaneously, a working memory match attracts the first saccade more profoundly than do mismatch objects, an effect that was present throughout the saccade latency distribution. These findings demonstrate that memory plays a fundamental biasing role in the earliest competitive processes in the selection of visual objects, even when working memory is not recruited during selection.