Midline theta dissociates agentic extraversion and anhedonic depression

The agency facet of extraversion is related to individual differences in reward anticipation and has been linked to the neurotransmitter dopamine. Dopamine has also been associated with components of anhedonia, which is one of the cardinal symptoms of depression and refers to lack of responsiveness to pleasurable stimuli. This raises the question whether low agency is associated with anhedonia symptoms in depression and if agency and anhedonia are characterized by similar neurobiological mechanisms. To address this hypothesis, we tested whether questionnaire measures of agency and anhedonia are correlated within depressed (n = 20) and non-depressed (n = 22) participants. Further, we investigated whether dopamine-related signatures in the EEG recorded during a gambling task (feedback-evoked theta activity, and frontal versus posterior theta activity) similarly relate to agency and anhedonia. Results indicated that anhedonia was significantly elevated in the depression group, and negatively correlated with agency. However, while theta activity evoked by negative vs. positive feedback was sensitive to anhedonia and depression status but unrelated to agency, frontal versus parietal theta activity predicted agency, but was unrelated to anhedonia and depression. Together, this double dissociation suggests that in spite of considerable phenotypical overlap, anhedonia and agency may be linked to partially distinct neurobiological markers.     

Laboratory-induced learned helplessness attenuates approach motivation as indexed by posterior versus frontal theta activity

Research suggests that midline posterior versus frontal electroencephalographic (EEG) theta activity (PFTA) may reflect a novel neurophysiological index of approach motivation. Elevated PFTA has been associated with approach-related tendencies both at rest and during laboratory tasks designed to enhance approach motivation. PFTA is sensitive to changes in dopamine signaling within the fronto-striatal neural circuit, which is centrally involved in approach motivation, reward processing, and goal-directed behavior. To date, however, no studies have examined PFTA during a laboratory task designed to reduce approach motivation or goal-directed behavior. Considerable animal and human research supports the hypothesis put forth by the learned helplessness theory that exposure to uncontrollable aversive stimuli decreases approach motivation by inducing a state of perceived uncontrollability. Accordingly, the present study examined the effect of perceived uncontrollability (i.e., learned helplessness) on PFTA. EEG data were collected from 74 participants (mean age = 19.21 years; 40 females) exposed to either Controllable (n = 26) or Uncontrollable (n = 25) aversive noise bursts, or a No-Noise Condition (n = 23). In line with prediction, individuals exposed to uncontrollable aversive noise bursts displayed a significant decrease in PFTA, reflecting reduced approach motivation, relative to both individuals exposed to controllable noise bursts or the No-Noise Condition. There was no relationship between perceived uncontrollability and frontal EEG alpha asymmetry, another commonly used neurophysiological index of approach motivation. Results have implications for understanding the neurophysiology of approach motivation and establishing PFTA as a neurophysiological index of approach-related tendencies.     

Frontal theta power linked to neuroticism and avoidance

Approach–avoidance conflict is thought to generate negative affective bias, mediated by theta rhythms. This process is distinct from, and adds to, the effects of simple aversive input. We assessed this distinction by holding gain constant and increasing loss value so that conflict and simple aversion peaked in the conflict (gain equals loss) and loss (net loss) conditions, respectively. Right frontal areas showed increases in both conflict- and loss-induced theta power. However, loss, but not conflict, power was correlated with avoidance and neuroticism, showing a Gender x Hemisphere interaction. We concluded that multiple aversive processes converge in lateral frontal networks and that individual differences in theta response in these networks may reflect differences in behavioural and emotional reactivity to aversive events.     

Immobility-related hippocampal theta activity in rats during reaction to novelty

Two types of theta activity are seen in the hippocampal formation of the rat. Type 1 theta which has a high overall frequency is related to movements, whereas Type 2 theta of lower frequency is related to immobility. The purpose of the present study was to investigate whether Type 2 theta may occur in rats encountering novelty. To shed light on this issue rats were tested in a novelty test in which smell made up the novel aspect. Upon encountering a cheese spot on the novel object the rats displayed relatively high-frequency theta activity while all legs were immobile, and low level of EMG activity was seen in the nuchal muscle. It was not possible to test whether the "novelty theta" was sensitive to atropine, since administration of atropine sulphate abolished the rats' preference for novelty. The results are discussed in terms of Type 2 theta reflecting sensory processing.     

Expectation and temperament moderate amygdala and dorsal anterior cingulate cortex responses to fear faces

A chronic tendency to avoid novelty is often the result of a temperamental bias called inhibited temperament, and is associated with increased risk for anxiety disorders. Neuroimaging studies have demonstrated that an inhibited temperament is associated with increased amygdalar blood-oxygenation-level-dependent (BOLD) response to unfamiliar faces that were not expected; however, the effects of variations in expectancy remain unknown. Using functional magnetic resonance imaging (fMRI), we studied BOLD response to infrequently encountered fear faces that were either expected or not expected in 42 adults with an inhibited or an uninhibited temperament. Individuals with an inhibited temperament had greater amygdala, but less dorsal anterior cingulate cortex (dACC), BOLD response when the stimuli were expected. In contrast, those with an uninhibited temperament had a smaller amygdala but larger dorsal anterior cingulate cortex BOLD response when expecting to see fear faces. These findings demonstrate temperament differences in expectancy effects and provide preliminary evidence for the dACC as a neural substrate mediating differences in inhibited temperament. Enhanced amygdala sensitivity coupled with weak inhibitory control from the dACC may form a neural circuit mediating behaviors characteristic of inhibited temperament and risk for anxiety disorders.     

Overcoming suppression in order to remember: Contributions from anterior cingulate and ventrolateral prefrontal cortex

The ability to remember is often compromised by competition from irrelevant memories. However, acts of selective remembering can alter the competitive relationship between memories; memories that are selected against are weakened, whereas those that are retrieved are strengthened. Whereas the weakening of selectedagainst memories is typically evidenced by subsequently poorer recall of these memories, the present study tested the hypothesis that when previously selected-against memories can subsequently be successfully retrieved, such acts of successful retrieval are associated with engagement of neurobiological mechanisms that serve to detect and overcome competition. Consistent with this hypothesis, fMRI revealed that anterior cingulate cortex and right ventrolateral prefrontal cortex are differentially engaged during successful retrieval of previously selected-against memories, and that their engagement is directly related to the magnitude of weakening that is induced by prior acts of selecting against these memories.     

Inactivation of the anterior cingulate cortex impairs extinction of rabbit jaw movement conditioning and prevents extinction-related inhibition of hippocampal activity

Although past research has highlighted the involvement of limbic structures such as the anterior cingulate cortex (ACC) and hippocampus in learning, few have addressed the nature of their interaction. The current study of rabbit jaw movement conditioning used a combination of reversible lesions and electrophysiology to examine the involvement of the hippocampus and the ACC during acquisition, performance, and extinction. We found that microinfusions of procaine into the ACC did not significantly alter the rate of behavioral learning or the amplitude of hippocampal conditioned unit responses, but that they disrupted the rhythmic periodicity of conditioned jaw movements. During extinction, whereas controls showed a rapid decline in behavioral CRs and active inhibition of hippocampal unit responses, ACC lesioned rabbits showed a persistence of conditioning-related hippocampal activity and behavioral responding. The results show that the ACC can be important for adaptive suppression of conditioned behavior and suggest a crucial physiological modulation of hippocampus by ACC during extinction.     

Human anterior and posterior hippocampus respond distinctly to state and trait anxiety

We examined whether anterior and posterior hippocampal subregions in humans show distinct relationships to state and trait anxiety. In rodents, the ventral (but not dorsal) hippocampus is critically involved in contextual anxiety, whereas dorsal hippocampus is affected by chronic stress and genetically bred trait anxiety. These studies suggest that state forms of anxiety may be more associated with anterior (ventral in rodents) hippocampus, whereas trait forms of anxiety maybe more associated with posterior (dorsal in rodents) hippocampus. Participants were placed under alternating blocks of threat of shock and safety conditions while performing a secondary task, and state and trait anxiety measures were obtained. Using subject-specific anatomically defined masks, we found that state anxiety was related to activity in anterior but not posterior hippocampus, whereas trait anxiety showed the opposite pattern. Additionally, a psychophysiological connectivity analysis showed that activity in anterior hippocampus was more strongly related to activity in ventromedial prefrontal cortex under threat than under safety conditions, significantly more so than activity in posterior hippocampus was. Hence, anterior hippocampus shows a distinct moment-to-moment connectivity profile with other neural regions during threat relative to posterior hippocampus. The findings provide several lines of evidence for functional differentiation of anterior and posterior hippocampal involvement across state and trait components of anxiety in humans.     

Differential perseverations in verbal retrieval related to anterior and posterior left hemisphere lesions

Sixty-two patients with focal cerebral lesions and 11 control patients were examined using alternating tasks of learning, generation, and recall of words beginning with "K." The results supported the hypothesis that "recurrent" and "stuck-in-set" varieties of perserveration are related to posterior and anterior left hemisphere lesions, respectively. Patients with left posterior lesions usually failed to suppress the expression of previously generated words in the subsequent generation task, whereas patients with left anterior lesions stated a greater number of new (incorrect) words in the recall of previously learned words, presumed to indicate stuck-in-set perseveration of the previous generation performance.     

Enhanced occipital and anterior cingulate activation in men but not in women during exposure to angry and fearful male faces

Blood-oxygenation-level-dependent signal was measured with functional magnetic resonance imaging in 24 healthy young subjects (12 men and 12 women) during viewing of angry, fearful, and neutral male and female face pictures. Exposure to angry male as opposed to angry female faces activated the visual cortex and the anterior cingulate gyrus significantly more in men than in women. A similar sex-differential brain activation pattern was present during exposure to fearful but not neutral faces. Previous behavioral studies indicate enhanced physiological arousal in men but not in women during exposure to angry male as opposed to female faces, and brain imaging studies have shown that the occipital cortex and the anterior cingulate gyrus are influenced by activity in the autonomic nervous system as well as by visual attention. Hence, we suggest that the elevated occipital and anterior cingulate activation in men during confrontation with other angry and fearful males may reflect enhanced vigilance in a potentially dangerous situation.     

Risk assessment behaviors associated with corticosterone trigger the defense reaction to social isolation in rats: role of the anterior cingulate cortex

The extent to which the hypothalamic-pituitary-adrenal axis is activated by short-term and long-term consequences of stress is still open to investigation. This study aimed to determine (i) the correlation between plasma corticosterone and exploratory behavior exhibited by rats subjected to the elevated plus maze (EPM) following different periods of social isolation, (ii) the effects of the corticosterone synthesis blocker, metyrapone, on the behavioral consequences of isolation, and (iii) whether corticosterone produces its effects through an action on the anterior cingulate cortex, area 1 (Cg1). Rats were subjected to 30-min, 2-h, 24-h, or 7-day isolation periods before EPM exposure and plasma corticosterone assessments. Isolation for longer periods of time produced greater anxiogenic-like effects on the EPM. However, stretched attend posture (SAP) and plasma corticosterone concentrations were increased significantly after 30?min of isolation. Among all of the behavioral categories measured in the EPM, only SAP positively correlated with plasma corticosterone. Metyrapone injected prior to the 24?h isolation period reversed the anxiogenic effects of isolation. Moreover, corticosterone injected into the Cg1 produced a selective increase in SAP. These findings indicate that risk assessment behavior induced by the action of corticosterone on Cg1 neurons initiates a cascade of defensive responses during exposure to stressors.     

Disentangling the effects of choice and intensity on affective response to and preference for self-selected- versus imposed-intensity physical activity

ObjectiveTo examine the independent effects of physical activity (PA) intensity and choice of PA intensity when comparing affective response to and relative preference for self-selected-intensity versus imposed higher intensity PA.DesignWithin-subjects experiment.MethodsTwenty-nine healthy, low-active women completed four PA bouts over two sessions. The first session consisted of a one-third mile self-selected-intensity treadmill walk during which the speed was recorded, but was not visible to the participants. The second session consisted of three, counterbalanced, one-third mile treadmill conditions: (a) self-selected intensity, (b) same intensity as recorded for the first-session-self-selected-intensity walk, but with the intensity imposed by the experimenter (i.e., yoked-self-selected intensity), and (c) intensity set at 20% higher than the first-session-self-selected-intensity walk (imposed higher intensity). Acute affective valence (pleasure/displeasure) was recorded prior to, during, and following each walking bout. Preference for each walking intensity was assessed using a behavioral-choice paradigm.ResultsContrary to hypotheses, there was no effect of condition on acute affective valence. However, consistent with hypotheses, there was a linear trend, F(1, 22) = 11.00, p = .003, indicating preference in descending order from self-selected-intensity to yoked-self-selected-intensity to imposed higher intensity PA.ConclusionsBoth choice over the intensity and a lower intensity per se contributed to greater preference for self-selected-intensity over imposed higher intensity PA among healthy low-active women; however, there was no evidence to support the notion that affective response to PA mediated this relationship.     

The effect of posterior lobe extract, adrenalin, and pilocarpine on the response of the thyroid gland to the thyreoactivator hormone of the anterior lobe of the hypophysis

The studies reported here were directed toward ascertaining in a variety of organisms whether or not any of the three lobes of the pituitary gland affected thyroid activity. We documented a thyroid stimulating action of the anterior lobe of the pituitary gland extract that was not shared in by either the intermediate or posterior lobes. Pilocarpine first depressed the stimulating action of the pituitary extract but, after the fifth injection, it accentuated the response of the thyroid gland to the pituitary extract. Highlights of a thesis submitted to the faculty of the graduate school of the University of Maryland in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Editor’s Comment: Konstantin Sudakov is a renowned physiologist who directs the institute in Moscow that is dedicated to P.K. Anokhin. Anokhin worked with Pavlov during the 1920s and became Professor of Physiology at the Gorky Institute. Professor Sudakov recounts the history of Anokhin’s extension of Pavlov’s theory of conditioned reflex to a concept of functional systems.