Exploring the Neurophysiological Processes Involved in Fear Conditioning in Animals (Essay Sample)

The Neurophysiological Processes Involved in Fear Conditioning in Animals
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The Neurophysiological Processes Involved in Fear Conditioning in Animals
All animals, including human beings, traverse a subtle trade-off throughout their lives. One of the things that are essential for the survival of both of them is forecasting potential danger/threat and taking the appropriate reaction. However, too much anxiety and fear can have adverse effects on other behaviors that are essential for evolutionary fitness, and in the case of human beings, it results in severe impairment of their quality of life. In order to maintain this balance in an environment that is ever succumbing to change, animals depend on mechanisms that allow them to adapt to new threats. Neurobiological research studies conducted in recent decades have showcased the neural substrates of such behavioral adaptations in rodents (Kim & Jung, 2006). A rapidly growing catalog of experimental research studies maps the neural circuitry of fear learning in both great details, and a sophisticated arrangement of numerous brain structures comes about, with one of them being the amygdala (Miller et al., 2019). As this circuitry’s complexity continues to become more apparent, the need for theoretical clarification only becomes more exigent.
Fear Conditioning
Fear conditioning takes place when primarily innocuous CS (conditioned stimulus) gets paired contingently with an aversive unconditional stimulus that is responsible for insentient activating unconditioned fear responses (Mertens et al., 2020). Via the above-mentioned association(Conditioning stimuli-Unconditioning stimuli) formation, the conditioned stimulus comes to prompt numerous conditioned responses sharing the same physiognomies to innate fear responses. Little Albert's experiment conducted by Rayner and Watson in the year 1920 is one of the examples of fear conditioning (Watson, 2019). Little Albert, an infant aged 11 months, initially showcased curiosity by touching as well as playing with a white rat. As the infant’s hand touched the rodent, the back of his head got banged by the experimenters with a steel bar with a mallet. This resulted in little Albert to startle, fall forward, and began crying (Unconditioned stimulus). Thereafter, after the rodent (conditioned stimulus) was positioned near the infant’s hand, he extracted his hand and started cry (conditioned stimulus). This display of fear to the rodent was purported to have widespread to other objects as well as furry animals.
Contemporary investigations tailored to fear conditioning normally use small mammals such as rabbits, mice, and rats as experimental subjects. Apart from that, they also employ a tone as a conditioned stimulus as well as an unconditioned stimulus (mild electric shock). According to Keller et al. (2020), under these particular conditions, a very small number of conditioned stimulus-unconditioned stimulus pairings generate a lot of fear learning, as substantiated by various fear responses showcased upon successive expositions of the conditioning stimulus. It is noteworthy that, whereas most neurobiological research studies use simple temporal pairings of conditioning stimulus and unconditioned stimulus to generate fear conditioning, it is the informational correlation between the US and CS that is the important determining factor of classical conditioning (Kim & Jung, 2006). Typical fear indices in rats include movement arrest, analgesia, musculature reflexes enhancement, ultrasonic distress vocalization, and changes in autonomic system activities. Since fear conditioning takes place quickly and has a lasting impact, this task has turned out to be a popular behavioral tool used to study learning and memory's cellular-molecular substrates.
Fear can also be swiftly attained via operant or instrumental conditioning in which an averse stimulus's presentation is conditional upon an animal's behavior. One of the most employed processes with rodents is the inhibitory or passive avoidance task in which their response gets followed by a foot shock. As a function of stimulus pairing (cs-us), the animal is able to learn how to avert, making the response that was trailed by the aversive experience. Though procedurally diverse, it is assumed that fear reminiscences that are obtained through conditioned fear as well as through inhibitory avoidance (instrumental conditioning) eventually share a common neural substrate. Nevertheless, these two lines of research studies have often generated contradictory results.
The Role of Amygdala in Fear Conditioning
According to a large body of research studies, the amygdala is the key neural system sub-serving fear conditioning. The above-mentioned structure has been alleged to be essential for emotional processing not only in animals but also in human beings. This was first described in relation to research studies of Kluver-Bucy syndrome (Lanska, 2018). The said syndrome is branded by a set of uncommon behaviors witnessed in monkeys after the removal of their temporal lobes. Monkeys having such lesions developed the inability to comprehend the significance of visual stimuli, and they approached, ate, and orally scrutinized dangerous objects such as snakes without reluctance. Apart from that, the monkeys were also able to attain a change in both their emotional and social behavior (Sun et al., 2020). For instance, they showcased escalated tameness towards their caretakers and loss of fear. Monkeys that once averted their caretakers’ presence began to approach and make contact with them after their temporal lobes were gotten rid of.
About twenty years later, Weiskrantz tried to localize the impacts that contribute to the behavioral changes witnessed in monkeys. His study evaluated the above-mentioned structure's role in the avoidance of behaviors observed in monkeys during fear conditioning (Cuevas & Sheya, 2019). He established that an intact amygdala is required by learning and memory motivated by fear. Therefore, the researcher found that amygdalactomy was responsible for impairing the identification performance of fear-avoidance as well as fearful stimuli. After the role of the amygdala in identifying fearful stimuli as well as fear-avoidance behavior was discovered, numerous studies were then conducted to further investigate why the amygdala's lesions alter reactions to intimidating stimuli. According to Lay, (2017), through their studies, Richard & Blanchard (1972), we're able to demonstrate that bilateral damage to the amygdala of a rat played a critical role in the changes of reaction towards intimidating/threatening stimuli, which in their research was a cat. (Richard & Blanchard, 1972). Therefore, amygdala lesions eradicated the cat's freezing response and made the rodents (rats) approach it without fear.
Fear Learning Neural Substrates
Basolateral Amygdala
Main Connection
The amygdala’s basolateral complex is premeditated as the main site in which fear memories are acquired and stored. The basolateral amygdala can be divided into accessory basal nuclei, lateral and basal. Amygdala’s prominent role is already ostensive in its neuroanatomical structure. Sensory modalities projections that carry information associated with conditioned stimuli and form structures known to convey nociceptive signals congregate in the basolateral amygdala, which serves as the major recipient of the external inputs, the amygdala. Especially, sensory inputs are received by the LA from all sensory modalities through the thalamus and the cortex. These particular inputs can get subdivided into indirect projections through the neocortex and direct projections from the sensory thalamus (Sun et al., 2020). Apart from that, the basolateral amygdala gets supplied with polymodal inputs from various sources. Some of these inputs are from the hippocampus, rhinal cortices, and from prefrontal cortex. It is thought that the prefrontal inputs play a significant role in intermediating behavioral flexibility, whereas the hippocampal and rhinal inputs transmit information about context as well as contextual memory. These particular connections are reciprocal, showing the basolateral amygdala’s role in both the formation and organization of memory in the HPC and mPFC.
Fear and Extinction Neurons in the Basolateral Amygdala
Conditioned stimuli activity in the LA lessened in some neurons apparently by depotentiation of thalamic inputs during extinction learning. However, it remains constant in others. Extinction learning in the basolateral amygdala is linked with a switch in conditioning stimuli-evoked activity amid two principal neurons’ subpopulations. At the start of extinction training, one of the populations showcases high conditioned stimuli-evoked activity (Sun et al., 2020). This correlates with the behavioral countenance of fear and is thus labeled as fear neurons. However, aroused/evoked activity progressively declines in the course of extinction learning. The extinction neurons, which is another population, acts in the opposite manner as there is minimal to no conditioned stimuli-arousal activity at the start but during extinction, the neurons acquire conditioned stimuli-evoked responses. The decline in conditioned responding is preceded by this switch in neural activity. A third population of principal neurons, on the other hand, is resistant to extinction learning.
Mechanistically, the activity of both extinction and fear neurons showcases mutual competition. This has resulted in the hypothesis that the intra-B inhibitory n...