Browsing by Subject "Motivation"

Motivated behaviors are essential for the survival and maintenance of life. The ventral tegmental area (VTA) is a midbrain region that has been implicated in motivational processes, such as seeking reward and avoiding harm. It contains dopamine (DA) neurons that project to limbic brain areas and give rise to the prominent mesolimbic DA pathway. In addition, it contains gamma-aminobutyric acid (GABA) neurons that also project to the limbic system as well as other major brain regions, such as the hindbrain and prefrontal cortex. Despite decades of research, the functions of VTA neurons remain mysterious and controversial. According to an influential hypothesis, VTA DA neurons encode a reward prediction error (RPE), a teaching signal that updates the value of learned associations (Schultz, Dayan, & Montague, 1997). It has also been proposed that VTA GABA neurons represent reward expectancy and provide the subtraction needed (actual reward minus expected reward), to compute a RPE (Eshel et al., 2015). According to another prominent hypothesis, however, VTA neurons encode the amount of effort, vigor, or ‘incentive’ we attribute to motivationally relevant stimuli (Salamone & Correa, 2012; Berridge & Robinson 1998). In most studies that attempt to relate VTA neural activity with reinforcement learning (RL) algorithms, the animals are often head-fixed and behavioral measures are usually limited to limb movements or licking. However, restraining the animal does not mean that they do not attempt to move their head and body. This creates a significant confound in all past research on DA neurons encoding RPE. I will argue that the conflict between the two prominent hypotheses of VTA function arises from both conceptual and empirical limitations, including the lack of precise and continuous behavioral measurements. To address these concerns, I first developed a novel head-fixation device that measures the forces exerted by the head in three orthogonal directions (up/down, left/right, forward/backward), as well as the forces exerted by the body (Chapter 2). The device contains load cells that convert analog voltage signals into continuous measures of force while the mice engage in traditional head-fixed tasks. By recording VTA neurons using in vivo electrophysiology and optogenetics while simultaneously measuring the continuous forces exerted by the mice, I found that VTA DA neurons encode the impulse vector (the magnitude and direction of force exerted over time) rather than RPE (Chapter 3). Moreover, according to the impulse-momentum theorem, I show how dynamic vector representations from head-fixed experiments can be translated into kinematic vector representations during freely moving behavior. According to the impulse-momentum theorem, impulse is equal to a change in momentum. In other words, a change in force is equivalent to a change in velocity assuming a constant mass, linking both dynamic and kinematic vector quantities. Then, by using the same continuous force measurements and manipulating the spatial location of reward during a traditional Pavlovian conditioning task, I falsified several key predictions from the RPE hypothesis (Chapter 4). By delivering the same reward in different locations (e.g., keeping the value and prediction constant), I was able to disambiguate an RPE signal from force exertion. I found that VTA DA neurons more precisely represented the impulse vector and not an RPE. Moreover, using a leaky integrator model, single unit activity of DA neurons could be used to predict the forces exerted across time regardless of reward predictability, as well as across multiple timescales. Then, I demonstrated that optogenetic manipulation of phasic DA activity has no impact on learning but directly modulates performance. At the same time, by using the same manipulations, I falsified the expectancy hypothesis of VTA GABA neurons and demonstrated they also represent vector quantities of force rather than expectancy. I found that VTA GABA neurons show opponent activity (increases or decreases of their firing rate) based on the direction of movement, despite the same level of expectancy and value (Chapter 4). Moreover, I utilized the leaky-integrator model to show that VTA GABA neurons represent the integral of DA activity. Finally, using in vivo electrophysiology, optogenetics, in vivo calcium imaging, and 3D motion capture during freely moving behavior in a novel reward tracking task, I found that a subset of VTA GABA neurons precisely represent three-dimensional rotational kinematics (Chapter 5). Taken together, these results demonstrate that the VTA controls the kinematics and dynamics necessary to control all motivated behaviors such as orientation, approach, and avoidance; whether to seek reward or avoid harm. These data unite the directional and activational components of motivation and provide precise physical quantities to influential concepts such as effort and vigor. Furthermore, I show the computational interaction between VTA DA and GABA neurons and demonstrate how they both participate in controlling the force vectors. Consequently, I made significant steps towards understanding how the VTA controls motivated behaviors and also falsified several key predictions of the RPE hypothesis, as well as improved the effort-related hypotheses. Thus, I have developed a new and comprehensive framework of VTA functioning.

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The brain’s dopaminergic system is critical to adaptive behaviors, and is centrally implicated in various pathologies. For decades, research has aimed at better characterizing what drives the mesolimbic dopamine system and the resulting influence on brain physiology and behavior in both humans and animals. To date, the dominant modes of research have relied on extrinsic approaches: pharmacological manipulations, direct brain stimulation, or delivering behavioral incentives in laboratory tasks. A critical open question concerns whether individuals can modulate activation within this system volitionally. That is, can individuals use self-generated thoughts and imagery to invigorate this system on their own? This process can be referred to as “cognitive neurostimulation” -- a precise and non-invasive stimulation of neural systems via cognitive and behavioral strategies. And if not, can they be taught to do so? Recent technological advances make it feasible to present human participants with information about ongoing neural activations in a fast and spatially precise manner. Such feedback signals might enable individuals to eventually learn to control neural systems via fine-tuning of behavioral strategies. The studies described herein investigate whether individuals can learn to volitionally invigorate activation within the mesolimbic reward network. We demonstrate that under the right training context, individuals can successfully learn to generate cognitive states that elicit and sustain activation in the ventral tegmental area (VTA), the source of dopamine production within the mesolimbic network. Although participants were explicitly trained to increase VTA activation, multiple mesolimbic regions exhibited increased connectivity during and after training. Together, these findings suggest new frameworks for aligning psychological and biological perspectives, and for understanding and harnessing the power of neuromodulatory systems.

Pursuing valued goals is a fundamental aspect of human behavior. In this dissertation, I explore the tendency of observers to underestimate the extent to which members of disadvantaged groups value their goals. Nine studies (N = 3,851) find evidence of a goal-value bias, such that people perceive goals across a variety of domains as more valuable to high-socioeconomic status (SES) individuals than to low-SES individuals (Studies 1 – 7), that these perceptions do not accurately reflect reality (Pilot and Study 3), and that those who are strongly motivated to justify inequality show the bias to a greater extent (Studies 1, 2a, 2b, and 7). In addition to motivated processes, I also test the extent to which these effects result from an inference error, such that people rely too heavily on an outcome-value association when judging value. Weakening the association between outcomes and goal value by considering additional factors that affect outcomes (e.g., time/effort, obstacles) reduces the bias (Studies 4, 6, and 7). Finally, I explore downstream implications of the bias, finding that people give greater support to high-SES individuals than to low-SES individuals, a discriminatory outcome that is partially driven by perceived goal value (Studies 5, 6, and 7). Across nine studies, I show that people expect higher-SES individuals to value achieving goals more than their lower-SES counterparts, and that this bias can lead people to support those who are already ahead.

Memories are not veridical representations of the environment. Rather, an individual's goals can influence how the surrounding environment is represented in long-term memory. The present dissertation aims to delineate the influence of reward and punishment motivation on human declarative memory encoding and its underlying neural circuitry. Chapter 1 provides a theoretical framework for investigating motivation's influence on declarative memory. This chapter will review the animal and human literatures on declarative memory encoding, reward and punishment motivation, and motivation's influence on learning and memory. Chapter 2 presents a study examining the behavioral effects of reward and punishment motivation on declarative memory encoding. Chapter 3 presents a study examining the neural circuitry underlying punishment-motivated declarative encoding using functional magnetic resonance imaging (fMRI), and compares these findings to previous studies of reward-motivated declarative encoding. Chapter 4 presents a study examining the influence of reward and punishment motivation on neural sensitivity to and declarative memory for unexpected events encountered during goal pursuit using fMRI. Finally, Chapter 5 synthesizes these results and proposes a model of how and why motivational valence has distinct influences on declarative memory encoding. Results indicated that behaviorally, reward motivation resulted in more enriched representations of the environment compared to punishment motivation. Neurally, these motivational states engaged distinct neuromodulatory systems and medial temporal lobe (MTL) targets during encoding. Specifically, results indicated that reward motivation supports interactions between the ventral tegmental area and the hippocampus, whereas, punishment motivation supports interactions between the amygdala and parahippocampal cortex. Together, these findings suggest that reward and punishment engage distinct systems of encoding and result in the storage of qualitatively different representations of the environment into long-term memory.

In this dissertation, I propose, operationalize, and test a novel model of identity fragility using fragile masculinity as a case study. To date, identity research has largely focused on understanding how people’s membership in different social categories (e.g., gender, race) shapes their experiences, self-concept, and behavior. I contend that when (i) a social category is high-status and (ii) its corresponding norms are especially rigid—as is often the case with masculinity—people in this category may feel pressured to uphold its norms in order to maintain their status. To the extent that identities are pressured, I argue that they are “fragile”, in turn eliciting compensatory, stereotypical responses (e.g., male aggression) to perceived threats aimed at maintaining status. Supporting the proposed model, I found that young men’s (Study 1) and post-pubertal boys’ (Study 3) aggressive cognition post-threat was directly related to the extent to which their masculine behavior was extrinsically motivated (pressured). In Study 2, I found that straight men’s anti-gay bias was again predicted by a combination of extrinsic pressure and threat, which was partially mediated by men’s endorsement of gender-inversion stereotypes (e.g., gay = feminine). Finally, as one possible pathway to reduce these adverse pressures and compensatory aggression, in Study 4, I found that identity-salient events like U.S. presidential elections can loosen masculinity norms from the “top-down” to mitigate certain men’s sociopolitical aggression.

Anticipation is a state of expectancy for something that will happen, and it allows us to use past learning to prepare for and make predictions about the future. Studies have shown that anticipation influences behavioral performance, learning, and memory, and studies implicate reward-related brain circuitry. However, few studies have investigated the neural underpinnings of anticipation on a brain-wide network scale . In this set of experiments, I take an interdisciplinary cross-species approach, using in-vivo electrophysiology in mice and functional magnetic resonance imaging (fMRI) in humans, to investigate brain networks underlying anticipation in motivated behavior. Using a data-driven machine learning approach, I characterize the anticipatory network in mice running through a T-maze, and show how it is affected by behavioral perturbation in the form of a task reversal, and circuit perturbation in the form of a genetic mutant mouse line. I also validate this network in a separate cohort of mice in a variation of the T-maze task that varies in difficulty, and show how activity in this network is modulated by task difficulty and intermediate instrumental goals. Finally, I investigate this network using fMRI in human subjects performing a trivia-based task to show how this network links curiosity, a more intrinsic form of motivation, to memory. The findings from these studies provide evidence at multiple levels and across multiple species for an anticipatory network that links motivational state to cognitive performance.

An abstract of a dissertation that examines the motivational foundations of social networks. Five studies using diverse methods examine goal pursuit as an antecedent to social network structure, finding that self-oriented and affiliation-oriented goal pursuit evoke unique patterns of interpersonal perception and motivation which lead to the development of sparser and denser social networks, respectively. Study 1 serves as an empirical summary of our theorizing: individuals primed with dense networks feel more efficacious pursuing affiliation-oriented goals versus self-oriented goals, and individuals primed with sparse networks feel more efficacious pursuing self-oriented goals than individuals primed with dense networks. Study 2finds a correlation between personal goals and network structure. Studies 3 and 4 experimentally demonstrate that reminders of self versus affiliation-oriented goals lead to different cognitively-activated network structures. Study 5 finds that individuals entering a new social network with strong career goals (self-oriented goals) develop significantly sparser local networks and attain more central network positions; the opposite pattern emerges for individuals pursuing strong social goals (affiliation-oriented goals). Individuals strongly motivated to pursue both goals lose the network structure benefits of having a strong career goal. Findings support the hypothesis linking personal goal pursuit to network structure, a novel approach to integrating psychology and networks research.

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Biological drives such as hunger, thirst, and sexual reproduction are potent motivators of behavior. Extrinsic rewards in the environment (i.e. food, drink, money) are also important behavioral and cognitive motivators. In addition to the relevance of an extrinsic reward in meeting the needs of biological drives, an individual’s sensitivity to the physiological state of their body (interoceptive awareness) would also be expected to mediate motivation for these extrinsic primary rewards (i.e. food, drink). Importantly, a better characterization of the predicted behavioral and neural interactions between interoception, motivation, and memory systems can highlight novel targets for interventions to facilitate motivation and memory for adaptive behaviors and/or impede motivation and memory for maladaptive behaviors (i.e. addiction, relapse, overeating).

The present dissertation examines how individual differences in interoceptive awareness may modulate motivated memory formation via motivational and affective mechanisms. Specifically, interoceptive accuracy is associated with increased motivation for relevant primary rewards and enhanced encoding for these rewards. However, anxiety, negatively predicted by interoceptive accuracy, negatively predicts memory the next day. Furthermore, memory for relevant primary rewards was negatively predicted by insula-parahippocampal and ventral tegmental area-hippocampal background connectivity.

Three studies examine individuals' implicit sensitivity to the absence of motivation perceived in others and how the nature of this sensitivity is moderated by individuals' own motivational states. Using a subliminal priming paradigm, Study 1 tested a direct perception-behavior link between perceiving indifference in others and applying such indifference towards one's own pursuits. Study 2 then examined how individuals who are primed in advance with a nonconscious achievement goal show automatic counteraction to the indifference perceived in others. Using a video-based priming paradigm, Study 3 then found that such goal-driven counteraction to indifference occurred only among individuals with higher action control--those who had the ability to sustain goal pursuit after the intention to pursue it has been formed. In contrast, individuals with lower action control in Study 3 were more susceptible to indifference than all other participants, particularly when an achievement goal was made highly active in memory. These influences were found in all three studies to occur largely without participants' conscious intent or awareness.

Background: Self Determination Theory (SDT) conceptualizes human motivation in terms of a spectrum. However, literature is scarce on how to measure self-determination in different languages or how self-determination can influence the effectiveness of healthcare interventions. The aim of this study was to translate and culturally adapt a psychometric questionnaire on self-determination (TSRQ) as well as SMS booster messages for a Brief Intervention (BI) aimed at reducing harmful alcohol use among injury patients presenting at Kilimanjaro Christian Medical Centre (KCMC) in Moshi, Tanzania.

Methods: A mixed-methods approach was used to evaluate the psychometric properties of the TSRQ and SMS booster messages. Likert-scale surveys were administered on expert panels to assess translation quality and adherence to theory.

Results: Quantitative analyses confirmed that the Swahili translation of the TSRQ accurately reflected SDT constructs. Exploratory Factor Analysis (EFA) revealed a two-domain model had a better fit than the original three-domain TSRQ. Expert panel surveys indicated that the SMS booster messages maintained strong connections to tenets of SDT.

Conclusion: This was the first study to conduct a cross-cultural validation of the TSRQ in Tanzania and the first to implement and assess motivational constructs in SMS booster messages for a BI to promote safe alcohol use. The TSRQ is a valid, clinically useful scale but could be improved with more items. SMS booster messages touch on many SDT constructs, affirming their motivational utility.