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Behavioral Neuroscience - Vol 131, Iss 5

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Behavioral Neuroscience The primary mission of Behavioral Neuroscience is to publish original research papers in the broad field of the biological bases of behavior.
Copyright 2017 American Psychological Association
  • Neonatal perirhinal cortex lesions impair monkeys’ ability to modulate their emotional responses.
    The medial temporal lobe (MTL) is a collection of brain regions best known for their role in perception, memory, and emotional behavior. Within the MTL, the perirhinal cortex (PRh) plays a critical role in perceptual representation and recognition memory, although its contribution to emotional regulation is still debated. Here, rhesus monkeys with neonatal perirhinal lesions (Neo-PRh) and controls (Neo-C) were tested on the Human Intruder (HI) task at 2 months, 4.5 months, and 5 years of age to assess the role of the PRh in the development of emotional behaviors. The HI task presents a tiered social threat to which typically developing animals modulate their emotional responses according to the level of threat. Unlike animals with neonatal amygdala or hippocampal lesions, Neo-PRh animals were not broadly hyper- or hyporesponsive to the threat presented by the HI task as compared with controls. Instead, Neo-PRh animals displayed an impaired ability to modulate their freezing and anxiety-like behavioral responses according to the varying levels of threat. Impaired transmission of perceptual representation generated by the PRh to the amygdala and hippocampus may explain the animals’ inability to appropriately assess and react to complex social stimuli. Neo-PRh animals also displayed fewer hostile behaviors in infancy and more coo vocalizations in adulthood. Neither stress-reactive nor basal cortisol levels were affected by the Neo-PRh lesions. Overall, these results suggest that the PRh is indirectly involved in the expression of emotional behavior and that effects of Neo-PRh lesions are dissociable from neonatal lesions to other temporal lobe structures. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • Overriding actions in Parkinson’s disease: Impaired stopping and changing of motor responses.
    We administered a stop-change paradigm, an extended version of the stop task that requires (a) stopping an ongoing motor response and (b) changing to an alternative (change) response. Performance of a group of patients diagnosed with Parkinson’s disease (PD) and taking dopaminergic medication was compared with that of matched healthy control (HC) participants. Behavioral results indicated that response latencies to the initial go signal did not distinguish between the 2 groups, but that stopping latencies were prolonged in PD patients. In addition, the change response was delayed in the clinical group, indicating difficulties in flexibly changing to alternative motor actions upon external cues. The change deficit in PD related to the inhibition deficit. This dependence points to a serial processing architecture in PD according to which the stopping process has to finish before the change process can be initiated. In contrast, the HC group showed parallel stop and change processing. Analyses of sequential trial effects suggest that both HC and PD patients are susceptible to aftereffects of action override, due to the consequences of the automatic retrieval of recent associations between action and goal representations. Interestingly, postchange performance of the clinical group was hampered disproportionately, suggesting that PD is associated with an impairment in overriding previously formed action-goal associations. These findings support the notion that both higher-order cognitive control processes, such as inhibiting and changing actions, as well as lower-order feature binding mechanisms rely on basal ganglia functioning and are compromised by the basal ganglia dysfunction caused by PD. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • Ventral striatum lesions do not affect reinforcement learning with deterministic outcomes on slow time scales.
    A large body of work has implicated the ventral striatum (VS) in aspects of reinforcement learning (RL). However, less work has directly examined the effects of lesions in the VS, or other forms of inactivation, on 2-armed bandit RL tasks. We have recently found that lesions in the VS in macaque monkeys affect learning with stochastic schedules but have minimal effects with deterministic schedules. The reasons for this are not currently clear. Because our previous work used short intertrial intervals, one possibility is that the animals were using working memory to bridge stimulus-reward associations from 1 trial to the next. In the present study, we examined learning of 60 pairs of objects, in which the animals received only 1 trial per day with each pair. The large number of object pairs and the long interval (approximately 24 hr) between trials with a given pair minimized the chances that the animals could use working memory to bridge trials. We found that monkeys with VS lesions were unimpaired relative to controls, which suggests that animals with VS lesions can still learn to select rewarded objects even when they cannot make use of working memory. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • Effects of intra-accumbal administration of dopamine and ionotropic glutamate receptor drugs on delay discounting performance in rats.
    Nucleus accumbens core (NAcc) has been implicated in impulsive choice, as measured in delay discounting. The role of dopamine (DA) in impulsive choice has received considerable attention, whereas glutamate (Glu) has recently been shown to be an important mediator of discounting. However, research has not examined how DA or Glu receptors in NAcc mediate different aspects of delay discounting performance, that is, (a) sensitivity to reinforcer magnitude and (b) sensitivity to delayed reinforcement. Adult male Sprague–Dawley rats were first trained in a delay discounting task, in which the delay to a large magnitude food reinforcer increased across blocks of trials. Following behavioral training, rats received bilateral implantation of guide cannulas into NAcc. Half of the rats (n = 12) received infusions of the DA-selective ligands SKF 38393 (D1-like agonist: 0.03 or 0.1 μg), SCH 23390 (D1-like antagonist: 0.3 or 1.0 μg), quinpirole (D2-like agonist: 0.3 or 1.0 μg), and eticlopride (D2-like antagonist: 0.3 or 1.0 μg). The other half received infusions of the ionotropic Glu ligands MK-801 (NMDA uncompetitive antagonist: 0.3 or 1.0 μg), AP-5 (NMDA competitive antagonist: 0.3 or 1.0 μg), ifenprodil (noncompetitive antagonist at NR2B-containing NMDA receptors: 0.3 or 1.0 μg), and CNQX (AMPA competitive antagonist: 0.2 or 0.5 μg). Results showed that SCH 23390 (0.3 μg) decreased sensitivity to reinforcer magnitude without altering impulsive choice, whereas ifenprodil (1.0 μg) decreased sensitivity to delayed reinforcement (i.e., impulsive choice). The current results show that DA and NMDA receptors in NAcc mediate distinct aspects of discounting performance. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • The effect of scopolamine on matching behavior and the estimation of relative reward magnitude.
    We investigated the behavioral effects of scopolamine on rats that bar pressed for trains of electrically stimulating pulses under concurrent variable interval schedules of reward. For the first half of the session (30 min) a 1:4 ratio in the programmed number of stimulation trains delivered at each option was in effect. At the start of the second half of the session, an unsignaled reversal in the relative train number (4:1) occurred. We tracked the relative magnitude of reward estimated for each contiguous pair of reinforced visits to competing options. Scopolamine hydrobromide led to a reduction in the relative magnitude of reward. A similar result was obtained in a follow-up test in which relative magnitude was manipulated by varying the pulse frequency of stimulation, while equating the train number at each option. The effect of scopolamine hydrobromide could not be attributed to undermatching, side bias, nor to an effect of scopolamine on the reward integration process. When the same rats were treated with scopolamine methylbromide, no effects on matching behavior were observed. Our results suggest a cholinergic basis for the computation of choice variables related to matching behavior. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • Disentangling the effects of serotonin on risk perception: S-carriers of 5-HTTLPR are primarily concerned with the magnitude of the outcomes, not the uncertainty.
    Serotonin signaling is vital for reward processing, and hence, also for decision-making. The serotonin transporter gene linked polymorphic region (5-HTTLPR) has been connected to decision making, suggesting that short-allele carriers (s) are more risk averse than long-allele homozygotes (ll). However, previous research has not identified if this occurs because s-carriers (i) are more sensitive to the uncertainty of the outcomes or (ii) are more sensitive to the magnitude of the outcomes. This issue was disentangled using a willingness-to-pay task, where the participants evaluated prospects involving certain gains, uncertain gains, and ambiguous gains. The results clearly favored the hypothesis that s-carriers react more to the magnitude of the outcomes. Self-reported measures of everyday risk-taking behavior also favored this hypothesis. We discuss how these results are in line with recent research on the serotonergic impact on reward processing. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • Strain-dependent sex differences in a long-term forced swim paradigm.
    Women are twice as likely as men to suffer from trauma- and stressor-related disorders. The development of improved therapeutic interventions is contingent upon a more complete grasp of both the neural and behavioral dynamics of the stress response in females. The rodent forced swim test (FST) is a valuable animal model for exploring the neurobiological mechanisms responsible for selection of active and passive responses to inescapable stressors, but it is often neglected in 2-day FST studies is the dissociation of innate (Day 1) versus learned (Day 2) coping responses. Here, we used a modified, long-term (4-week) FST paradigm and immunohistological analysis to study the interactions of sex, strain, and housing arrangement on selection of active and passive coping strategies in Sprague Dawley (SD) and Long Evans (LE) rats. We observed significant strain × sex interactions in both forced swim sessions with respect to both passive (immobility) and active (climbing and headshakes) responses. In immobility measures, we observed stable sex differences in SD rats and a stable lack of sex differences in LE rats across tests. In addition, both SD and LE females displayed significantly more headshakes than males during Test 1 and more climbing in Test 2. Most notably, males, but not females, exhibited a cross-test increase in immobility, suggesting that males and females may engage different learning processes in a 2-day FST. These sex differences corresponded to c-fos expression in the medial prefrontal cortex (mPFC), indicating that the mPFC may contribute to sexually dimorphic behavior in the FST. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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  • Context-specific habituation of the freezing response in newborn chicks.
    Previous studies have found that in mature animals habituation is context-specific in some species but not in others. Given the mixed evidence present in the literature, we decided to explore whether habituation is context-specific in newborn chicks. The results showed that 3 days after hatching, chicks were capable of using global contextual information to rapidly habituate their freezing response to a series of sudden acoustic stimuli. Our study is the 1st to show context-specific habituation in this avian species, a result in agreement with those of previous findings in adult male zebra finches (Taeniopygia guttata). Furthermore, although our study does not intend to provide a systematic investigation of the ontogeny of habituation in this species, our findings show that a few days after hatching, juvenile chicks are capable of a sophisticated associative learning process that takes into account complex environmental information. (PsycINFO Database Record (c) 2017 APA, all rights reserved)
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