Failure of motor function-A Developmental Embodiment Research perspective on the systemic effects of stress

Humans are capable to skillfully perform a huge variety of complex movements seemingly effortless and to flexibly adjust movement execution to ever-changing environmental conditions, often without apparent differences in the movement outcome. This impressive ability has sparked scientific interest in the mechanisms underlying movement execution for decades. In this perspective article, we argue that investigating the processes and mechanisms leading to failure of motor functions is a fruitful approach to advance the field of human motor neuroscience and beyond. The study of failure of motor function in specific populations (patient groups, skilled experts) has already provided tremendous insight in the systemic characteristics and multi-level functional dependencies of movement execution. However, particularly the transient failure of function in everyday motor actions remains a blind spot. Coming from the perspective of Developmental Embodiment Research, we argue that the integration of a developmental embodiment and lifespan perspective with existing systemic and multi-level methodological approaches of failure of function analyses provides an integrative, interdisciplinary framework, which will allow us to overcome this shortcoming. We further suggest that stress-induced failure of motor function situations might represent a promising starting point for this endeavor. Identifying the involved cross-level functional dependencies of acute and chronic stress on transient and persistent motor functioning would further advance our knowledge on the mechanisms underlying movement execution, and would allow to identify targets for intervention and prevention across the whole spectrum of motor function and failure.

A Developmental Framework for Embodiment Research: The Next Step Toward Integrating Concepts and Methods

Embodiment research is at a turning point. There is an increasing amount of data and studies investigating embodiment phenomena and their role in mental processing and functions from across a wide range of disciplines and theoretical schools within the life sciences. However, the integration of behavioral data with data from different biological levels is challenging for the involved research fields such as movement psychology, social and developmental neuroscience, computational psychosomatics, social and behavioral epigenetics, human-centered robotics, and many more. This highlights the need for an interdisciplinary framework of embodiment research. In addition, there is a growing need for a cross-disciplinary consensus on level-specific criteria of embodiment. We propose that a developmental perspective on embodiment is able to provide a framework for overcoming such pressing issues, providing analytical tools to link timescales and levels of embodiment specific to the function under study, uncovering the underlying developmental processes, clarifying level-specific embodiment criteria, and providing a matrix and platform to bridge disciplinary boundaries among the involved research fields.

Highs and lows: Genetic susceptibility to daily events

Why people differ in their susceptibility to external events is essential to our understanding of personality, human development, and mental disorders. Genes explain a substantial portion of these differences. Specifically, genes influencing the serotonin system are hypothesized to be differential susceptibility factors, determining a person’s reactivity to both positive and negative environments. We tested whether genetic variation in the serotonin transporter (5-HTTLPR) is a differential susceptibility factor for daily events. Participants (N = 326, 77% female, mean age = 25, range = 17–36) completed smartphone questionnaires four times a day over four to five days, measuring stressors, uplifts, positive and negative affect. Affect was predicted from environment valence in the previous hour on a within-person level using three-level autoregressive linear mixed models. The 5-HTTLPR fulfilled all criteria of a differential susceptibility factor: Positive affect in carriers of the short allele (S) was less reactive to both uplifts and stressors, compared to homozygous carriers of the long allele (L/L). This pattern might reflect relative affective inflexibility in S-allele carriers. Our study provides insight into the serotonin system’s general role in susceptibility and highlights the need to assess the whole spectrum of naturalistic experiences.

Oxytocin and the stress buffering effect of social company: a genetic study in daily life

Social relationships are a crucial determinant of both mental and physical health. This effect is partly due to social buffering of stress. Animal studies suggest that social buffering is mediated via the oxytocin system, while studies in humans are sparse and limited by the low ecological validity of laboratory settings. In the present study, participants (N = 326) completed smartphone questionnaires four times a day over 4 to 5 days, measuring stressors, negative affect, and social context to assess social buffering. We found that under stress, participants reported a higher need for social company. Further, the impact of prior stressful events on momentary negative affect was attenuated by the perceived pleasantness of current social company. This social buffering effect was moderated by haplotypes of the oxytocin receptor gene, based on two well-described single nucleotide polymorphisms (rs2268498, rs53576). Effects were robust when controlling for gender and age, applying different data quality criteria, and even apparent in genotype-based analyses. Our findings demonstrate that social buffering and its modulation by oxytocin system characteristics have implications for life as lived outside the laboratory.

Epigenetic Programming Effects of Early Life Stress: A Dual-Activation Hypothesis

Epigenetic processes during early brain development can function as 'developmental switches' that contribute to the stability of long-term effects of early environmental influences by programming central feedback mechanisms of the HPA axis and other neural networks. In this thematic review, we summarize accumulated evidence for a dual-activation of stress-related and sensory networks underlying the epigenetic programming effects of early life stress. We discuss findings indicating epigenetic programming of stress-related genes with impact on HPA axis function, the interaction of epigenetic mechanisms with neural activity in stress-related neural networks, epigenetic effects of glucocorticoid exposure, and the impact of stress on sensory development. Based on these findings, we propose that the combined activation of stress-related neural networks and stressor-specific sensory networks leads to both neural and hormonal priming of the epigenetic machinery, which sensitizes these networks for developmental programming effects. This allows stressor-specific adaptations later in life, but may also lead to functional mal-adaptations, depending on timing and intensity of the stressor. Finally, we discuss methodological and clinical implications of the dual-activation hypothesis. We emphasize that, in addition to modifications in stress-related networks, we need to account for functional modifications in sensory networks and their epigenetic underpinnings to elucidate the long-term effects of early life stress.

Optogenetic Destabilization of the Memory Trace in CA1: Insights into Reconsolidation and Retrieval Processes

Reactivation of memory can cause instability necessitating the reconsolidation of the trace. This process can be blocked by amnestic treatments administered after memory reactivation resulting in subsequent memory deficits. While the basolateral amygdala (BLA) is known to be crucial for reconsolidation, evidence for a contribution of the hippocampal CA1 region has only started to accumulate. Moreover, the effect of a reconsolidation blockade in CA1 has only been evaluated behaviorally, and it is unknown whether this manipulation has a long-term effect on neuronal activity. We combined optogenetic and high-resolution molecular imaging techniques to inhibit cell firing in CA1 following the reactivation of a fear memory in mice, evaluated memory performance and imaged neuronal activity the next day upon reexposure to the conditioning context. Blocking memory reconsolidation led to severe memory impairments that were associated with reduced neuronal activity not only in CA1 but also in CA3 and the BLA. Thus, our results indicate that CA1 is necessary for reconsolidation and suggest the involvement of a CA3-CA1-BLA network in the retrieval of contextual fear memory. Further investigations of this network might contribute to the validation of new brain targets for the treatment of pathologies such as posttraumatic stress disorders.

The generational brain: Introduction

In contemporary society, the image of the “flexible brain” and the notion of neuroplasticity are increasingly replacing that of the static mature brain. Brains and neurons are considered to be constantly generated and regenerated. Age cohort comparisons and longitudinal studies introduce a developmental perspective to the field. However, these articulations and investigations occur within a sociopolitical field marked by vested interests and the celebration of all things neural. Utilizing the notion of “the generational brain,” we propose that it is fruitful to exploit the polysemity of the word “generation,” as well as the historicity of scientific concepts and methods, to interrogate and re/formulate questions currently addressed in developmental neuroscience in particular and neuroscience in general. This special issue’s contributions provide an early impression of what a “critical friendship” with developmental neuroscience, aware of its sociocultural and epistemological implications as well as the historicity of concepts, may look like.

Imaging a memory trace over half a life-time in the medial temporal lobe reveals a time-limited role of CA3 neurons in retrieval

Whether retrieval still depends on the hippocampus as memories age or relies then on cortical areas remains a major controversy. Despite evidence for a functional segregation between CA1, CA3 and parahippocampal areas, their specific role within this frame is unclear. Especially, the contribution of CA3 is questionable as very remote memories might be too degraded to be used for pattern completion. To identify the specific role of these areas, we imaged brain activity in mice during retrieval of recent, early remote and very remote fear memories by detecting the immediate-early gene Arc. Investigating correlates of the memory trace over an extended period allowed us to report that, in contrast to CA1, CA3 is no longer recruited in very remote retrieval. Conversely, we showed that parahippocampal areas are then maximally engaged. These results suggest a shift from a greater contribution of the trisynaptic loop to the temporoammonic pathway for retrieval.

DOI:http://dx.doi.org/10.7554/eLife.11862.001

There are two schools of thought about what role the hippocampus – a region of the brain – plays in memory. Some neuroscientists think that it is involved in retrieving all memories. Others believe that its contribution is restricted to the retrieval of recent memories, while a neighboring part of the brain called the parahippocampal region takes over to retrieve older memories.

The hippocampus contains two distinct areas called CA1 and CA3, which have recently been suggested to have, at least partially, separate roles. For example. previous studies have shown that CA3 plays an important role in processes that tend to be less efficient as time goes by. However, it remains unclear whether CA1 and CA3 contribute equally to the retrieval of recent and older memories.

Lux et al. addressed this question by observing brain activity in mice as they retrieved recent and older memories. The experiments show that both areas of the hippocampus are involved in retrieving recent memories, but that only the CA1 area is involved in the retrieval of older memories. The parahippocampal region is much more active during the retrieval of older memories than recent ones.

These findings clarify the role of the hippocampus in memory by showing that it is involved in the retrieval of both recent and older memories. The next steps will be to better understand how the CA1 and CA3 areas contribute to memory and to pin point the specific molecular mechanisms these regions rely on to do so.

DOI:http://dx.doi.org/10.7554/eLife.11862.002

Caffeine improves left hemisphere processing of positive words

A positivity advantage is known in emotional word recognition in that positive words are consistently processed faster and with fewer errors compared to emotionally neutral words. A similar advantage is not evident for negative words. Results of divided visual field studies, where stimuli are presented in either the left or right visual field and are initially processed by the contra-lateral brain hemisphere, point to a specificity of the language-dominant left hemisphere. The present study examined this effect by showing that the intake of caffeine further enhanced the recognition performance of positive, but not negative or neutral stimuli compared to a placebo control group. Because this effect was only present in the right visual field/left hemisphere condition, and based on the close link between caffeine intake and dopaminergic transmission, this result points to a dopaminergic explanation of the positivity advantage in emotional word recognition.

Deconstructing major depression: a validation study of the DSM-IV symptomatic criteria

BACKGROUND

The DSM-IV symptomatic criteria for major depression (MD) derive primarily from clinical experience with modest empirical support.

METHOD

The sample studied included 1015 (518 males, 497 females) Caucasian twins from a population-based registry who met criteria for MD in the year prior to the interview. Logistic regression analyses were conducted to compare the associations of: (1) single symptomatic criterion, (2) two groups of criteria reflecting cognitive and neurovegetative symptoms, with a wide range of potential validators including demographic factors, risk for future episodes, risk of MD in the co-twin, characteristics of the depressive episode, the pattern of co-morbidity and personality traits.

RESULTS

The individual symptomatic criteria showed widely varying associations with the pattern of co-morbidity, personality traits, features of the depressive episode and demographic characteristics. When examined separately, these two criteria groups showed robust differences in their patterns of association, with the validators with the cognitive criteria generally producing stronger associations than the neurovegetative.

CONCLUSIONS

Among depressed individuals, individual DSM-IV symptomatic criteria differ substantially in their predictive relationship with a range of clinical validators. These results challenge the equivalence assumption for the symptomatic criteria for MD and suggest a more than expected degree of 'covert' heterogeneity among these criteria. Part of this heterogeneity is captured by the distinction between cognitive versus neurovegetative symptoms, with cognitive symptoms being more strongly associated with most clinically relevant characteristics. Detailed psychometric evaluation of DSM-IV criteria is overdue.

The DSM-IV definition of severity of major depression: inter-relationship and validity

BACKGROUND

Severity is an important characteristic of major depression (MD) and an 'episode specifier' in DSM-IV classifying depressive episodes as 'mild', 'moderate' or 'severe'. These severity subtypes rely on three different measures of severity: number of criteria symptoms, severity of the symptoms and degree of functional disability. No prior empirical study has evaluated the coherence and validity of the DSM-IV definition of severity of MD.

METHOD

In a sample of 1015 (518 males, 497 females) Caucasian twins from a population-based registry who met criteria for MD in the year prior to interview, factor analysis and logistic regression were conducted to examine the inter-relationships of the three severity measures and their associations with a wide range of potential validators including demographic factors, risk for future episodes, risk of MD in the co-twin, characteristics of the depressive episode, the pattern of co-morbidity, and personality traits.

RESULTS

Correlations between the three severity measures were significant but moderate. Factor analysis indicated the existence of a general severity factor, but the factor was not highly coherent. The three severity measures showed differential predictive ability for most of the validators.

CONCLUSIONS

Severity of MD as defined by the DSM-IV is a multifaceted and heterogeneous construct. The three proposed severity measures reflect partly overlapping but partly independent domains with differential validity as assessed by a wide range of clinical characteristics. Clinicians should probably use a combination of severity measures as proposed in DSM-IV rather than privileging one.