Carissa J. Cascio

Dopamine D2 Receptors in the Nucleus Accumbens Are Important for Social Attachment in Female Prairie Voles (Microtus ochrogaster)

The prairie vole (Microtus ochrogaster), a monogamous rodent that forms long-lasting pair bonds, has proven useful for the neurobiological study of social attachment. In the laboratory, pair bonds can be assessed by testing for a partner preference, a choice test in which pair-bonded voles regularly prefer their partner to a conspecific stranger. Studies reported here investigate the role of dopamine D2-like receptors (i.e., D2, D3, and D4 receptors) in the nucleus accumbens (NAcc) for the formation of a partner preference in female voles. Mating facilitated partner preference formation and associated with an approximately 50% increase in extracellular dopamine in the NAcc. Microinjection of the D2 antagonist eticlopride into the NAcc (but not the prelimbic cortex) blocked the formation of a partner preference in mating voles, whereas the D2 agonist quinpirole facilitated formation of a partner preference in the absence of mating. Taken together, these results suggest that D2-like receptors in the NAcc are important for the mediation of social attachments in female voles.

Dopamine D2 Receptor-Mediated Regulation of Partner Preferences in Female Prairie Voles (Microtus ochrogaster}: A Mechanism for Pair Bonding?

This study examined the role of dopamine (DA) in partner preference (PP) formation in female prairie voles (Microtus ochrogaster). The nonspecific DA antagonist haloperidol blocked mating-induced PP, whereas the nonspecific DA agonist apomorphine induced PP without mating. The D2 antagonist eticlopride, but not the D1 antagonist SCH23390, blocked PP, whereas the D2 agonist quinpirole, but not the D1 agonist SKF38393, induced PP without mating. Injections of eticlopride before or immediately after mating, but not 24 hr after mating, impaired PP, indicating that DAs effects were not due to an interference with mating or sensory recognition. Finally, intracerebroventricular injections of eticlopride diminished PP. Together, these data suggest that mating-induced PP requires activation of D2 receptors and that social experience may activate dopaminergic pathways, with enduring effects on behavior.

Vibrotactile adaptation fails to enhance spatial localization in adults with autism.

A recent study [Tannan, V., Tommerdahl, M., Whitsel, B.L., 2006. Vibrotactile adaptation enhances spatial localization. Brain Res. 1102(1), 109-116 (Aug 2)] showed that pre-exposure of a skin region to a 5 s 25 Hz flutter stimulus (adaptation) results in an approximately 2-fold improvement in the ability of neurologically healthy human adults to localize mechanical stimulation delivered to the same skin region that received the adapting stimulation. Tannan et al. [Tannan, V., Tommerdahl, M., Whitsel, B.L., 2006. Vibrotactile adaptation enhances spatial localization. Brain Res. 1102(1), 109-116 (Aug 2)] proposed that tactile spatial discriminative performance is improved following adaptation because adaptation is accompanied by an increase in the spatial contrast in the response of contralateral primary somatosensory cortex (SI) to mechanical skin stimulation--an effect identified in previous imaging studies of SI cortex in anesthetized non-human primates [e.g., Simons, S.B., Tannan, V., Chiu, J., Favorov, O.V., Whitsel, B.L., Tommerdahl, M, 2005. Amplitude-dependency of response of SI cortex to flutter stimulation. BMC Neurosci. 6(1), 43 (Jun 21) ; Tommerdahl, M., Favorov, O.V., Whitsel, B.L., 2002. Optical imaging of intrinsic signals in somatosensory cortex. Behav. Brain Res. 135, 83-91; Whitsel, B.L., Favorov, O.V., Tommerdahl, M., Diamond, M., Juliano, S., Kelly, D., 1989. Dynamic processes govern the somatosensory cortical response to natural stimulation. In: Lund, J.S., (Ed.), Sensory Processing in the Mammalian Brain. Oxford Univ. Press, New York, 79-107]. In the experiments described in this report, a paradigm identical to that employed previously by Tannan et al. [Tannan, V., Tommerdahl, M., Whitsel, B.L., 2006. Vibrotactile adaptation enhances spatial localization. Brain Res. 1102(1), 109-116 (Aug 2)] was used to study adults with autism. The results demonstrate that although cutaneous localization performance of adults with autism is significantly better than the performance of control subjects when the period of adapting stimulation is short (i.e., 0.5 s), tactile spatial discriminative capacity remained unaltered in the same subjects when the duration of adapting stimulation was increased (to 5 s). Both the failure of prior history of tactile stimulation to alter tactile spatial localization in adults with autism, and the better-than-normal tactile localization performance of adults with autism when the period of adaptation is short are concluded to be attributable to the deficient cerebral cortical GABAergic inhibitory neurotransmission characteristic of this disorder.

Corpus callosum subdivision based on a probabilistic model of inter-hemispheric connectivity

Statistical shape analysis has become of increasing interest to the neuroimaging community due to its potential to locate morphological changes. In this paper, we present the a novel combination of shape analysis and Diffusion Tensor Image (DTI) Tractography to the computation of a probabilistic, model based corpus callosum (CC) subdivision. The probabilistic subdivision is based on the distances of arc-length parameterized corpus callosum contour points to trans-callosal DTI fibers associated with an automatic lobe subdivision. Our proposed subdivision method is automatic and reproducible, Its results are more stable than the Witelson subdivision scheme or other commonly applied schemes based on the CC bounding box. We present the application of our subdivision method to a small scale study of regional CC area growth in healthy subjects from age 2 to 4 years.

Social touch: A new vista for developmental cognitive neuroscience?

The past years have seen a renewed interest in measuring neural, physiological or cognitive, immediate and longer-term effects of human interaction through touch. The term “social touch” was rapidly adopted, implying the existence of (stimulus) selective and (functionally) specific mechanisms. It has been suggested that decreased exposure to social touch during development, either due to its unavailability (e.g. as in the case of pre-term infants placed in incubators or of infants of mothers with post-partum depression) or to atypical touch perception (e.g. as might be the case in autism) has serious consequences for subsequent brain and cognitive development. Despite the excitement surrounding this topic, and its clinical relevance, its object of study remained poorly defined and understood. The interest in social touch has a decades long history. The first rigorous studies into the importance of maternal physical contact for (monkey) development were carried out in the 1960s, by Harlow and col. (e.g. Harlow and Zimmermann, 1959). A few decades later, in the 1990s, Meaney and col. work reinforced the idea that close physical contact through licking and grooming, early in (rats’) life, was critical for the survival and thriving of the pups e.g. Liu et al., 1997). This group also revealed stable individual differences in the amount of care provided by mothers. It was only natural that researchers would ask whether similar phenomena can be described in human infants. Studying longitudinal cohorts, Field and col. and Feldman and col., demonstrated the beneficial effects of infant skin-to-skin contact or massage on later physical and mental development (e.g. Field et al., 2010, Feldman et al., 2013). These decades of very fruitful research have strongly reinforced the idea that caregiving through touch has a special and critical role in early development, and that interfering with it has long lasting effects (measurable still 10 years later, Feldman et al., 2013 or from one generation to the next, Champagne et al., 2008). The consistency across rodent, non-human primate, and human studies also seems to support the idea of a conserved mechanisms (in mammals). Differences in the nature of the critical stimulation (being able to cling to the surrogate mother matters in monkeys, Harlow and Zimmermann, 1959, while brushing the anal-genital region is sufficient to induce beneficial effects in mice, Evoniuk et al., 1979) could simply reflect species-specific ecological peculiarities, but ultimately serving the same function. Indeed, in both animal and human studies, parental touch was shown to modulate stress responsivity. However, even within one species – humans the variety of types of stimulation that have this effect (skin-to-skin contact or pressure massage) cannot but raise questions about how infants may identify caregiving touch across these instances. This is further complicated by the recent discovery of strong correlations between the perceived pleasantness of different stroking speeds and the tuning curves of a particular class of skin receptors, the CT-fibers (Löken et al., 2009). This research suggests that the speed and temperature of tactile stimulation might be the key properties triggering the effects of social touch. However, another mechanism needs to mediate the effect of skin-to-skin contact, which involves mainly static stimulation, and is therefore suboptimal for CT-fibers. In addition, many other studies showed that, in human adults, top-down factors, such as the identity of the person providing the stroking, matters more than the low-level properties of touch (Gazzola et al., 2012). Understanding the contribution of low level physical properties of touch versus that of the high level, social context, seems critical for understanding the role touch plays in development (and whether a unitary role can be at all ascribed to all touch provided by other human beings). Thus, this special issue emerged from the need to acknowledge, on one hand, a growing field of research into the role and the mechanisms of social interaction through touch and, on the other, the still lingering difficulties with defining the object of this research and understanding underlying developmental mechanisms. Introducing this special issue, Cascio et al. (2018) acknowledge the breadth of the research into social touch, which now includes molecular and physiological studies of skin receptors, studies of the social modulation of the perceived pleasantness of touch in human adults and of the atypicalities associated with developmental disorders, such as autism. They also review the small but growing literature looking into the mechanisms and neural substrates of social touch in infants. These authors highlight the need to integrate studies of social touch investigating low level properties of sensory systems with higher level aspects of social interaction. Interestingly, they suggest that few human touches are not social (i.e. non-intentional, accidental). While top-down cues to intentionality may be critical for perceived touch pleasantness later in life, other mechanisms must mediate the effects of social touch in the first months of life, before infants can judge the intentionality or goal-directedness of action.

Social touch and human development

Social touch is a powerful force in human development, shaping social reward, attachment, cognitive, communication, and emotional regulation from infancy and throughout life. In this review, we consider the question of how social touch is defined from both bottom-up and top-down perspectives. In the former category, there is a clear role for the C-touch (CT) system, which constitutes a unique submodality that mediates affective touch and contrasts with discriminative touch. Top-down factors such as culture, personal relationships, setting, gender, and other contextual influences are also important in defining and interpreting social touch. The critical role of social touch throughout the lifespan is considered, with special attention to infancy and young childhood, a time during which social touch and its neural, behavioral, and physiological contingencies contribute to reinforcement-based learning and impact a variety of developmental trajectories. Finally, the role of social touch in an example of disordered development –autism spectrum disorder—is reviewed.