Fear, conditioning, and aging: theoretical comment on LaBar et al. (2004)

Age-related impairments in associative learning have been found in studies using classical conditioning of motor responses. However, it is as yet unclear whether conditioning of fear responses is similarly affected by aging. K. S. La Bar et al. (2004) aimed to address this issue by studying age effects on fear conditioning applying a discrimination paradigm. Considering these results, this commentary discusses methodological issues in investigating fear conditioning as well as similarities and differences between associative learning of motor and autonomic responses with respect to neuronal substrates, susceptibility to aging, and the role of awareness of stimulus contingencies in mediating aging effects.     

Espresso reward learning, hold the dopamine: theoretical comment on Robinson et al. (2005)

Question: Is dopamine needed for reward learning? Answer: No--at least, not in the brain of a caffeinated dopamine-deficient (DD) mutant mouse. That is the conclusion of an important paper in this issue by S. Robinson, S. M. Sandstrom, V. H. Denenberg, and R. D. Palmiter (see record 2005-01705-001). Those authors demonstrate that reward learning can proceed normally in the brains of DD mice, even though they contain no dopamine at the time of learning, if the mice are given caffeine just before learning. Caffeine activates the DD mice by a nondopaminergic mechanism, allowing them to learn where to obtain food reward in a T-maze runway. Their reward-learning-without-dopamine is revealed on a subsequent test day, when dopamine function is restored by L-dopa administration. Robinson et al. conclude that dopamine is not needed for normal learning about rewards, or for hedonic "liking" of rewards during learning, but rather specifically for a motivational "wanting" component of reward, such as incentive salience.     

The construction of the maternal brain: theoretical comment on Kim et al. (2010)

Recently, there has been a spate of articles detailing the many and multifaceted alterations that define the Maternal Brain. The article by Kim et al. (2010) has provided a new "window" into the brain of the mother by the use of MRI showing structural changes in major regions over the period of the first few months, during which the intimate relationship between mother and infant forms. In this accompanying Commentary, we explore some connections between the animal work and the human data, and suggest some common pathways. In the end, it appears that maternal motivation, far from the intrinsic or instinctual state that many believe it to be, may, in fact, be attributable to many active processes "building" a responsive neural substrate. Like early brain development, itself a marvel of interacting genetic and environmental forces, the Maternal Brain may represent another developmental epoch in the life of the female. In this case, the alterations occur to promote the survival of subsequent generations and the care and protection of a most expensive mammalian metabolic and genetic investment. If so, is it possible that just as there are edifices that are poorly constructed and crumble at the first challenge by earthquake or hurricane, there may be defectively assembled maternal brains that fail in their task of caring adequately for young?     

Amyloid, hyperactivity, and metabolism: theoretical comment on Vloeberghs et al. (2008)

Recent data suggest that amyloid precursor protein transgenic mice consume excess calories relative to nontransgenic mice, yet they weigh less. Potential explanations include increased locomotor activity or increased basal metabolism. Mechanisms that might underlie the latter explanation include transmembrane pores produced by assemblies of A beta modifying proton or ion gradients across membranes. Alzheimer's disease also results in weight loss. If amyloid were found to induce a hypermetabolic state, this would suggest an alternative mechanism for the pathology found in the disease and provide opportunities for therapeutic strategies not yet considered.     

Effects of neonatal medial versus lateral temporal cortex injury: theoretical comment on Malkova et al. (2010)

The article by Malkova, Mishkin, Suomo, and Bachevalier (2010, this issue) adds an important piece to our understanding of the role of the medial versus lateral temporal regions in socioemotional behavior. In their paper, they evaluate the effect of infant and adult amygdala lesions and infant inferotemporal cortex lesions on the social interactions of monkeys in infancy and adulthood. The results show that medial temporal lesions performed in infants produce greater effects on socioaffective behavior than similar lesions in adulthood and that infant monkeys with inferotemporal lesions exhibit social deficits that are resolved by adulthood. These results are relevant to three significant issues: (1) the role of the medial temporal and lateral temporal cortex in the symptoms of the Kluver-Bucy syndrome; (2) the role of age at injury in behavioral change after cerebral injuries; and (3) the importance of lesion locus and behavioral measure for recovery from infant and adult cerebral injury.     

The mu-opioid receptor and the evolution of mother-infant attachment: theoretical comment on Higham et al. (2011)

Genetic variation at a single nucleotide polymorphism (SNP) in the mu-opioid receptor gene (OPRM1) of both humans and rhesus macaques Macaca mulatta has been associated with differential affinity to the endogenous ligand beta-endorphin as well as alterations in pain sensitivity, drug and alcohol dependence, and social behaviors. The new study by Higham et al. (2011) presented in the current issue of this journal shows for the first time that some of the natural variation in maternal behavior observed in rhesus macaque populations can also be explained by genetic differences at this SNP. This work, in conjunction with other recent studies showing that genetic variability at this same locus are related to changes in infant attachment, provides unique insights into how opioids have been reutilized during evolution to coordinate the mother-infant relationship.     

The importance of awareness for eyeblink conditioning is conditional: theoretical comment on Bellebaum and Daum (2004)

Eyeblink conditioning entails a variety of paradigms that differ in terms of the brain systems that support conditioning and the importance of awareness. In this issue, C. Bellebaum and I. Daum (2004) that reports that conditional discrimination learning depends on awareness. Their findings, along with other recent work, suggest a framework whereby the temporal features of the conditioning paradigm are critical in determining the ability of the cerebellum to support conditioning and, as a result, the role of awareness in conditioning.     

Aggression upon adolescent cocaine exposure linked to serotonin anomalies: theoretical comment on Ricci et al. (2004)

Aggressive tendencies may be linked to the psychopharmacology of cocaine, yet few experimental approaches have been brought to bear on understanding the neurobiological implications of cocaine exposure during the developmentally sensitive period of adolescence. In this issue, Melloni and coauthors (L. A. Ricci, J. M. Grimes, & R. H. Melloni, 2004) present convincing evidence that the development of serotonin signal cascades in key brain regions can be disrupted by cocaine administration, resulting in an aggressive response in adolescents. These findings may allow the development of new therapeutic approaches to tailor pharmacotherapy for adolescents experiencing problems with aggressive behavior and/or impulse control associated with illicit drug use.     

Biological implementation of the temporal difference algorithm for reinforcement learning: theoretical comment on O'Reilly et al. (2007)

The ability to survive in the world depends critically on the brain's capacity to detect earlier and earlier predictors of reward or punishment. The dominant theoretical perspective for understanding this capacity has been the temporal difference (TD) algorithm for reinforcement learning. In this issue of Behavioral Neuroscience, R. C. O'Reilly, M. J. Frank, T. E. Hazy, and B. Watz (2007) propose a new model dubbed primary value and learned value (PVLV) that is simpler than TD, and they claimed that it is biologically more realistic. In this commentary, the author suggests some slight modifications of a previous biological implementation of TD instead of adopting the new PVLV algorithm.     

Dopamine: helping males copulate for at least 200 million years: theoretical comment on Kleitz-Nelson et al. (2010)

Brain dopamine (DA) systems are implicated in a variety of behavioral responses and clinical syndromes, including sex, drug addiction, feeding, satiety, sleep, wakefulness, arousal, attention, reward, decision-making, depression, anxiety, psychosis, and movement disorders. The paper in this issue by Kleitz-Nelson, Dominguez, and Ball (2010) shows how DA release in the medial preoptic area of male quail are activated in an androgen-dependent manner during appetitive and consummatory phases of sexual behavior, similar to that reported previously in male rats. Those data suggest that the steroid-dependent role of hypothalamic DA in male sexual behavior has been conserved through evolutionary time.     

Persistent hunger for sodium makes brain stimulation not so sweet: theoretical comment on Morris et al. (2006)

The rewarding value of a stimulus is not fixed but rather is subjective and can vary with motivational state. M. J. Morris, E. S. Na, A. J. Grippo, and A. K. Johnson (2006) report that generating a prolonged sodium appetite decreases the rewarding value of lateral hypothalamic brain stimulation and sucrose intake. The findings support the idea that a specific motivational state can have strong, nonspecific consequences for reward processing. ((c) 2006 APA, all rights reserved).     

Impulsivity as a mediating mechanism between early-life adversity and addiction: theoretical comment on Lovic et al. (2011)

Early-life adversity, impulsivity, and dopaminergic function have all been implicated in adult drug addiction. The article by Lovic, Keen, Fletcher, and Fleming in this issue further elucidates this relationship by demonstrating that early-life adversity can increase impulsivity and decrease behavioral flexibility in adulthood. Recent literature suggests that these results are likely due to structural and functional changes in regions such as the orbitofrontal cortex (OFC) and nucleus accumbens (NAc), as well as altered dopamine activity. Impulsivity and behavioral inflexibility can increase susceptibility to addiction, and in turn, chronic substance abuse can impair the neurocircuitry underlying behavioral inhibition. Thus, early-life adversity may act as an entry point into a feed-forward spiral of impulsivity and addiction via the dysfunction of regions such as the OFC, NAc, and mesolimbic dopamine. (PsycINFO Database Record (c) 2011 APA, all rights reserved).     

Dopamine and reward: comment on Hernandez et al. (2006)

Many lines of evidence suggest that the dopaminergic projection from the midbrain tegmentum to the forebrain must play a critical role in mediating the behavioral effects of natural and artificial rewards, with brain stimulation reward and addictive drugs included in the latter category. However, a closer look reveals many incongruities. The work of G. Hernandez et al. (2006) resolves several puzzles. It implies that the dopaminergic projection does not carry the signal that encodes the magnitude of a brain stimulation reward. It suggests that the elevation in the tonic levels of dopamine consequent on brain stimulation reward modulates the registration of the magnitude of the reward. This reconciles the psychophysical evidence with the pharmacological, electrophysiological, and anatomical evidence. However, some serious puzzles do remain.     

Exploring the brain's interface between personality, mood, and emotion: theoretical comment on Canli et al. (2004)

T. Canli et al., 2004 use functional MRI to explore the neural interface between personality, mood, and emotional responses. Their finding of a double dissociation in brain response to emotional stimuli based on personality and mood state has significant implications for our understanding of the effects of personality traits and mood states on the neural bases of emotion and cognition.