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Neuroscience of Curiosity

Although the phenomenon of curiosity is widely regarded, its neural correlates still remain relatively unknown. However, recent studies have provided insight into the neurological mechanisms that may be associated with curiosity, such as learning, memory, and motivation. Such research aims to transition the study of curiosity from a speculative realm to one of more scientific credibility.

Current Theories

Curiosity-Drive Model

The curiosity-drive model states that experiences that are novel and complex create a sensation of uncertainty in the brain, a sensation perceived to be unpleasant. Curiosity acts as a means in which to dispel this uncertainty. By exhibiting curious and exploratory behavior, organisms are able to learn more about the novel stimulus and thus reduce the state of uncertainty in the brain. However, this model does not account for the observation that organisms display curiosity even in the absence of exciting and new stimuli . This type of exploratory behavior is common in many species. Take the example of a human toddler who, if bored in his current situation devoid of arousing stimuli, will walk about until something interesting is found. The observation of curiosity even in the absence of novel stimuli pinpoints one of the major shortcomings in the curiosity-drive model.

Optimal Arousal Model

The optimal-arousal model of curiosity posits that the brain aims to maintain an optimal level of arousal. If the stimulus is too intensely arousing, a “back-away” type behavior is engaged. In contrast, if the environment is boring and lacks exciting stimuli, exploratory behavior will be engaged until something optimally arousing is encountered. In essence, the brain is searching for the perfect balance of arousal states . This model aptly addresses the observation that organisms display curiosity even in the absence of novel and exciting stimuli. While this theory addresses some discrepancies in the curiosity-drive theory, it is not without fault. If there is an ideal state of curiosity that should be maintained in the brain, then gaining new knowledge to eliminate that state of curiosity would be considered counter-productive.

Integration of Reward Pathway

Taking into account the shortcomings of both curiosity-drive and optimal-arousal models, there have been attempts to integrate the neurological aspects of reward, wanting, and liking into a more comprehensive theory for curiosity, one that is explained by biological processes. The act of wanting new information involves mesolimbic dopamine activation, which assigns an intrinsic value to that new information that the brain then interprets as a reward. This is the neurobiology that motivates exploratory behavior. In addition, opioid activity in the nucleus accumbens evaluates stimuli and attaches an immediate value to the novel object, a sensation known as ‘liking’. This liking stimulates pleasure. The chemical processes of both wanting and liking play a role in activating the reward system of the brain, and perhaps in curious tendencies as well.

Neurological Aspects

Curiosity can be divided into many important neurological concepts:

Attention

Attention is the cognitive process by which one can selectively focus and concentrate on particular stimuli in the surrounding environment. There may be many stimuli in the surrounding area, but as there are limited cognitive and sensory resources, attention allows the brain to better focus on what it perceives to be the most important or relevant of these stimuli. Scientists can measure the amount of attention an individual devotes to a stimulus by tracking eye movements. Organisms focus their eyes on stimuli that are particularly stimulating or engaging; the more attention a stimulus garners, the more frequent the eye will be directed towards that stimulus. Normal individuals will look at new stimuli at least two to three times more often than familiar or repetitive stimuli. Exciting or novel stimuli demand more attention than stimuli perceived as boring .

Motivation and Reward

The drive to learn new information or perform some action is often initiated by the anticipation of reward. In this way, the concepts of motivation and reward are intrinsically tied to the phenomenon of curiosity.

Reward can be defined as an effect of some action that positively reinforces that behavior. Feelings of pleasure and satisfaction are often associated with reward. There are many areas in the brain used to process reward, such as the nucleus accumbens, the substantia nigra, the striata and the ventral tegmental area (VTA). These structures together form the reward pathway. There are many prominent neurotransmitters released in the activation of the reward pathway, the most relevant of which include dopamine, seratonin and opioid-derived chemicals. Recent studies have shown that dopamine may be important for the process of curiosity, most particularly in assigning and retained reward values for information gained. Midbrain dopamine neurons in monkeys are activated when determining the value of stimuli. There is some level of dopamine neuron activation when the reward of a familiar stimulus is already known, but perhaps more interestingly, there is a higher dopamine release when the reward is unknown and the stimulus is novel. Additionally, reward value were better retained (a function of both reward and memory) in monkeys that exhibited more curious behavior. Such studies implicate the reward pathway in curious behavior.

Memory and Learning

Memory is the process by which the brain can store and access information. While there is still much to be understood about both memory and curiosity, the two neurological processes seemed to be linked. Curiosity can defined as the urge to seek out novel stimuli. In order to determine if the stimulus is novel, an individual must remember if he has encountered the stimulus before or not. Thus, memory plays an integral role in dictating the level of novelty, and as such the level of curiosity. While one side of the coin dictates that memory affects curiosity, we can also flip the coin to project the converse relationship: curiosity affects memory. As previously mentioned, stimuli that are novel tend to capture more of our attention. Additionally, novel stimuli usually have a reward value associated with them, the anticipated reward of what learning that new information may bring. With stronger associations and more attention devoted to a stimulus, it is probable that the memory associated with that stimulus will be longer lasting and easier to recall, better facilitating learning.

Important neurological structures

While the neuroscience behind curiosity is still relatively unknown, certain neurological structures have been implicated in various aspects of curiosity:

Anterior cingulate cortex (ACC) and Anterior insular cortex (AIC)

Studies have observed through fMRI that both the anterior cingulate cortex (ACC) and the anterior insular cortex (AIC) were activated in the induction of perceptual curiosity. . These regions correspond to both conflict and arousal, and as such seem to reinforce certain curiosity explanatory models that include these principles.

Striata

The striata plays a role in attention and reward anticipation, both of which are important in the induction of curiosity.

Hippocampus and Parahippocampal Gyrus

The hippocampus is perhaps the most well known structure in memory formation and recall, and thus is important in determining the novelty of various stimuli. The parahippocampal gyrus (PHG) is the area of grey matter that surrounds the hippocampus and has recently been implicated in the process of curiosity. In one study, subjects were asked trivia questions and brain region activity was measured through fMRI. When subjects learned their answers to trivia questions were wrong, there was markedly increased activity in the PHG . Even if there was not a high level of curiosity when the question was initially asked, levels of curiosity were raised when the participant learned that his answer was wrong. This finding suggests that the PHG may be involved in the potentiation or amplification of curiosity more so than the primary induction of curiosity.

Amygdala

The amygdala consists of a pair of almond-shaped structure located deep within the medial temporal lobe. The amygdala is often associated with emotional processing, particularly for the emotion of fear, but is also important in memory. Certain studies suggest that amygdala is important is processing emotional reactions towards novel or unexpected stimuli and the induction of exploratory behavior. However, much still needs to be explored to understand the connection between curiosity levels and the amygdala.

Anterior pituitary

The anterior pituitary regulates the adrenal cortex, which releases cortisol, among other regulatory chemicals. Although mostly known for its role in stress, cortisol may also be associated with curious or exploratory behavior. Studies have shown that monkeys that have been administered small amounts of cortisol in early adolescence will display a higher degree of novelty seeking behavior later in life. However, the dose and frequency of cortisol administration was important. Monkeys subjected to normal levels of cortisol retained an average level of exploratory behavior, while those where were subjected to too much cortisol actually had a decrease in exploratory behavior. . These findings may support in part the optimal arousal theory, in which a small amount of stress encourages curious behavior, while too much stress initiates a "back away" response.

Nucleus accumbens

The nucleus accumbens is a formation of neurons that makes up the ventral striatum and is important in reward pathway activation. As previously mentioned, the reward pathway is an integral part in the induction of curiosity. The release of dopamine in animal models has been measured in investigating neurochemical response to novel or exciting stimuli. Dopamine transients, an indicator of dopamine release, were measured throughout life-stages of rats, as well as when rats were presented with various stimuli. Scientists observed more dopamine transients in early adolescent rats and in rats presented with novel or unexpected stimuli . These findings suggest that dopamine release in reward anticipation and pathway activation are intertwined with curiosity in both childhood and adult stages. The fast dopamine release observed during adolescence is particularly important, as curiosity and exploratory behavior are the largest facilitators of learning during early formative years.

Precuneus

The precuneus is located in the medial area of the superior parietal cortex and is involved in episodic memory and visuospatial processing. In animal models, the amount of grey matter in the precuneus was measured in normal monkeys and monkeys considered to be highly curious and exploratory. Results found that the more curious monkeys had a significantly higher density of grey matter in the precuneus region , suggesting that the precuneus density has an influence on levels of curiosity.

Caudate nucleus

Each hemisphere of the brain contains one caudate nucleus, a small C-shaped region that is highly responsive to dopamine. The caudate nucleus is another component in the reward pathway. The role of the caudate nucleus in curiosity was investigated by asking subjects trivia questions. fMRI was used to measure brain activity during the question period. Scientists observed that the caudate "lit up" when the participant was presented with trivia questions, indicating the anticipation of reward. In this case, the reward was the new information gained from learning the answer to the question. The results suggest that the caudate nucleus is relevant in the induction of curiosity.

Clinical Applications

Alzheimer's Disease

Predicting onset

Alzheimer's Disease (AD) is a neurodegenerative disease that affects memory ability of afflicted patients. Certain behavioral tests have been designed so as to predict the probability that an individual will develop AD. One such test uses the concepts of attention and curiosity for novel stimuli as a potential predictor for the disease. Subjects were presented with two images: one that they have seen, and one that they have not. Preference for each image was measured by tracking eye movements. Patient health and status was then monitored in the following years. Normal patients (those who did not develop AD) devoted two to three times more attention to novel stimuli. However, of those patients that concentrate on new stimuli less than half of the time, 100% went on to develop AD within four years . Such as behavior tests suggests that levels of curiosity may be a reliable indicator of the probability of developing AD.

After onset

The relationship between curiosity and dementia-related diseases may potentially be used to decrease the severity of symptoms. Patients with AD display many changes in spatial distribution of attention .It has been posited that these changes in attention could be corrected by improving emotional engagement to environmental stimuli by increasing the novelty or excitement factor of that stimulus. Emotional arousal engages more attentional resources in brain, which may then in turn form stronger associations in the brain. These associations ultimately result in better memory and reduced modulation of visuospatial attention, and therefore a decreased severity of AD symptoms. It is important to note that such treatments may not be effective for all patients due to the complexity and variability of AD.