Curiosity (from Latin curiosus "careful, diligent, curious," akin to cura "care") is a quality related to inquisitive thinking such as exploration, investigation, and learning, evident by observation in human and many animal species. The term can also be used to denote the behavior itself being caused by the emotion of curiosity. As this emotion represents a thirst for knowledge, curiosity is a major driving force behind scientific research and other disciplines of human study.
Causes
Although many living beings have an innate capability of curiosity, it should not be categorized as an instinct because it is not a fixed action pattern; rather it is an innate basic emotion because, while curiosity can be expressed in many ways, the expression of an instinct is typically more fixed and less flexible. Curiosity is common to human beings at all ages from infancy through adulthood, and is easy to observe in many other animal species. These include apes, cats, and rodents.
Brain
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. Various theories have been proposed in order to elucidate the mechanism of curiosity:
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
Due to the complexity of the subject, focusing on specific neural processes within curiosity can help in better understanding the phenomenon of curiosity as a whole. The following neural aspects can be thought of as essential sub-functions of curiosity:
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 (an emotional sensation of relief and happiness). 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 happiness. 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, serotonin and opioid-derived chemicals. Recent studies have shown that dopamine may be important for the process of curiosity, most particularly in assigning and retaining 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. Blocking the dopamine transporter (DAT) with GBR-12909 (i.e. Vanoxerine) and thereby increasing extracelluar dopamine levels is shown to increase the selection of novel choice options, despite uncertainty about their reward value. Additionally, reward values were better retained (a function of both reward and memory) in monkeys that exhibited more curious behavior. Such studies further 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 be 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 formed from that stimulus will be longer lasting and easier to recall, both of which facilitate better learning.
Important structures
While the neuroscience concerning curiosity is still relatively unknown, certain neuronal structures have been implicated in various aspects of curiosity:
- Anterior cortices: 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 explanatory models of curiosity that include these principles.
- Striatum: The striatum plays a role in attention and reward anticipation, both of which are important in the induction of curiosity.
- Hippocampus and dentate gyrus The hippocampus is important in memory formation and recall and therefore instrumental in determining the novelty of various stimuli. In addition, the dentate gyrus subregion of the hippocampus has been shown to be critical for regulating the spontaneous exploration of safe, novel spaces in mice. Since neither genetic nor molecular manipulation of the dentate gyrus in this study affected exploration of fearful or familiar spaces, it has been suggested that the dentate is somehow involved in generating or gating the underlying motivation to explore for the purpose of learning, a mental state in animals that may be akin to human curiosity. A prominent role for the dentate gyrus in exploration has since been independently demonstrated by other researchers.
- Parahippocampal gyrus: 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 structures 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 is tied to 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.
Impact from disease
Different neurodegenerative diseases can affect curiosity levels. Alzheimer's disease (AD) is a neurodegenerative disease that affects memory capability. Curiosity for novel stimuli might also be used as a potential predictor for the disease.
Morbid curiosity
A morbid curiosity exemplifies addictive curiosity. It has as its object death, violence, or any other event that may cause harm physically or emotionally, the addictive emotion being explainable by meta-emotions exercising pressure on the spontaneous curiosity itself. According to Aristotle in his Poetics we even "enjoy contemplating the most precise images of things whose sight is painful to us".
