Global InformationFear conditioning information
Pavlovian fear conditioning is a behavioral paradigm in which organisms learn to predict aversive events.[1] It is a form of learning in which an aversive stimulus (e.g. an electrical shock) is associated with a particular neutral context (e.g., a room) or neutral stimulus (e.g., a tone), resulting in the expression of fear responses to the originally neutral stimulus or context. This can be done by pairing the neutral stimulus with an aversive stimulus (e.g., an electric shock, loud noise, or unpleasant odor[2]). Eventually, the neutral stimulus alone can elicit the state of fear. In the vocabulary of classical conditioning, the neutral stimulus or context is the "conditional stimulus" (CS), the aversive stimulus is the "unconditional stimulus" (US), and the fear is the "conditional response" (CR).
Fear conditioning has been studied in numerous species, from snails[3] to humans.[4] In humans, conditioned fear is often measured with verbal report and galvanic skin response. In other animals, conditioned fear is often measured with freezing (a period of watchful immobility) or fear potentiated startle (the augmentation of the startle reflex by a fearful stimulus). Changes in heart rate, breathing, and muscle responses via electromyography can also be used to measure conditioned fear. A number of theorists have argued that conditioned fear coincides substantially with the mechanisms, both functional and neural, of clinical anxiety disorders.[5] Research into the acquisition, consolidation and extinction of conditioned fear promises to inform new drug based and psychotherapeutic treatments for an array of pathological conditions such as dissociation, phobias and post-traumatic stress disorder.[6]
Scientists have discovered that there is a set of brain connections that determine how fear memories are stored and recalled. While studying rats' ability to recall fear memories, researchers found a newly identified brain circuit is involved. Initially, the pre-limbic prefrontal cortex (PL) and the basolateral amygdala (BLA) were identified in memory recall. A week later, the central amygdala (CeA) and the paraventricular nucleus of the thalamus (PVT) were identified in memory recall, which are responsible for maintaining fear memories. This study shows how there are shifting circuits between short term recall and long term recall of fear memories. There is no change in behavior or response, only change in where the memory was recalled from.[7]
In addition to the amygdala, the hippocampus and the anterior cingulate cortex are important in fear conditioning. Fear conditioning in the rat is stored at early times in the hippocampus, with alterations in hippocampal gene expression observed at 1 hour and 24 hours after the event.[8] In the mouse, changed gene expression is also seen in the hippocampus at one hour and 24 hours after fear conditioning. These changes are transient in the hippocampal neurons, and almost none are present in the hippocampus after four weeks. By 4 weeks after the event, the memory of the fear conditioning event is more permanently stored in the anterior cingulate cortex.[9][10][11]
- ^ Maren S (2001). "Neurobiology of Pavlovian fear conditioning". Annual Review of Neuroscience. 24: 897–931. doi:10.1146/annurev.neuro.24.1.897. hdl:2027.42/61939. PMID 11520922.
- ^ Wallace KJ, Rosen JB (October 2000). "Predator odor as an unconditioned fear stimulus in rats: elicitation of freezing by trimethylthiazoline, a component of fox feces". Behavioral Neuroscience. 114 (5): 912–22. doi:10.1037/0735-7044.114.5.912. PMID 11085605.
- ^ Walters ET, Carew TJ, Kandel ER (January 1981). "Associative Learning in Aplysia: evidence for conditioned fear in an invertebrate". Science. 211 (4481): 504–6. Bibcode:1981Sci...211..504W. doi:10.1126/science.7192881. PMID 7192881.
- ^ Critchley HD, Mathias CJ, Dolan RJ (February 2002). "Fear conditioning in humans: the influence of awareness and autonomic arousal on functional neuroanatomy". Neuron. 33 (4): 653–63. doi:10.1016/s0896-6273(02)00588-3. PMID 11856537.
- ^ Rosen JB, Schulkin J (April 1998). "From normal fear to pathological anxiety". Psychological Review. 105 (2): 325–50. doi:10.1037/0033-295X.105.2.325. PMID 9577241.
- ^ VanElzakker MB, Dahlgren MK, Davis FC, Dubois S, Shin LM (September 2014). "From Pavlov to PTSD: the extinction of conditioned fear in rodents, humans, and anxiety disorders". Neurobiology of Learning and Memory. 113: 3–18. doi:10.1016/j.nlm.2013.11.014. PMC 4156287. PMID 24321650.
- ^ Yeager A (19 January 2015). "Newly identified brain circuit hints at how fear memories are made" (PDF). Science News.
- ^ Duke CG, Kennedy AJ, Gavin CF, Day JJ, Sweatt JD (July 2017). "Experience-dependent epigenomic reorganization in the hippocampus". Learn Mem. 24 (7): 278–288. doi:10.1101/lm.045112.117. PMC 5473107. PMID 28620075.
- ^ Halder R, Hennion M, Vidal RO, Shomroni O, Rahman RU, Rajput A, Centeno TP, van Bebber F, Capece V, Garcia Vizcaino JC, Schuetz AL, Burkhardt S, Benito E, Navarro Sala M, Javan SB, Haass C, Schmid B, Fischer A, Bonn S (January 2016). "DNA methylation changes in plasticity genes accompany the formation and maintenance of memory". Nat Neurosci. 19 (1): 102–10. doi:10.1038/nn.4194. PMID 26656643. S2CID 1173959.
- ^ Frankland PW, Bontempi B, Talton LE, Kaczmarek L, Silva AJ (May 2004). "The involvement of the anterior cingulate cortex in remote contextual fear memory". Science. 304 (5672): 881–3. Bibcode:2004Sci...304..881F. doi:10.1126/science.1094804. PMID 15131309. S2CID 15893863.
- ^ Kim JJ, Jung MW (2006). "Neural circuits and mechanisms involved in Pavlovian fear conditioning: a critical review". Neurosci Biobehav Rev. 30 (2): 188–202. doi:10.1016/j.neubiorev.2005.06.005. PMC 4342048. PMID 16120461.