Animal Behavior/Learning< Animal Behavior
Learning is characterized by persistent and measurable changes in behavior which are not associated with fatigue, altered motivation, or maturation. Some information or knowledge is acquired and is then used to alter the individuals actions and responses. Learning as an adaptive behavior allows individuals to adapt to specific environment challenges.
The mode of learning THAT develops in the absence of its association with any reinforcement is called non-associative learning. It is of following two types: Habituation and Sensitization: Habituation refers to a gradual decrease in behavioral responses with repeated encounters of a particular stimulus, which proves of no consequence. It depends on a change in the synapse between the sensory and motor neuron. Indepedent of conscious motivation or awareness it aids in distinguishing novel and meaningful information from the general background noise. Sensory Adaptation refers to a change in the responsiveness of a sensory system when confronted with a constant stimulus.
In contrast, sensitization refers to an increase in behavioral responses following repeated applications of a particular stimulus. Following sensitization, very little stimulation is then required to produce exceedingly large effects. Initial. light stimulation of peripheral skin receptors may not activate nociceptive (i.e., pain) neurons of the spinal cord. Continued, repeated stimulation of the same pathways will bring about central sensitization suggesting the presence of an irritating or potential more damaging skin issue. Tissue damage or continued inflammation may thereby cause chronic pain conditions. In long-term potentiation (LTP), physiological effects of subsequent synaptic signals are strengthened following initial activation. This process is thought to form an integral component of memory and learning. Repeated stimulation of different neural centers can also stengthen coordinated neuronal firing and thereby lead to seizures.
The ability to learn is a basic foundation of intelligence. Humans are particularly keen observers of the world around them and are thereby able to reliably identify the presence of different regularities and generalizations. Patterns that are of consequence to our daily lives are readily learned, which suggests the presence of powerful biases in their search and representation. We tend to remember information more easily if we have uncovered it ourselves than if they are simply presented to us.
An effort to form mental images out of any material to be learned may often enhance retention. Dual Code Theory suggests that most information can be committed to memory in either verbal/linguistic code or mental image code. The use of multiple codes for harnessing any material thus may enhance performance by increasing the number of retrieval paths.
A form of associative learning, Classical conditioning requires an unconditional reflex, where an unconditional stimulus (US) elicits an automatic, unlearned (unconditional) response (UR). If a neutral stimulus (NS) tends to precede it, an association is made and the conditional response (CR) becomes transferred onto the (previously neutral) conditional strimulus (CS); a conditional reflex has been learned. For instance, food (US) elicits salivation (UR) in a dog as a natural response. If the sound of a bell (NS) frequently occurs before the food (US) is presented then the mere sound of the bell (CS) will elicit salivation (CR). A mistranslation of "conditional" as "conditioned" meant that in English the CS and CR were referred to as conditioned stimulus and conditioned response, and the verb "to condition" was derived to refer to the process responsible for the establishment of new CR. (From: The Dictionary of Ethology and Animal Learning Edited by Rom Harre and Roger Lamb, The MIT Press, 1986)
Fear conditioning allows organisms to acquire affective responses, such as fear, in situations where a particular context or stimulus is predictably elicits fear via an aversive context (e.g., a shock, loud noise, or unpleasant odor). Little Albert Experiment
Conditioned Taste Aversion (i.e., Garcia conditioning) occurs when a subject experiences symptoms of a toxic, spoiled, or poisonous substance such as nausea, sickness, or vomiting after consuming unfamiliar food. Learned aversion of such taste is an adaptive trait that trains the body to stay away from items that are likely poisonous (e.g., berries or mushroom). This association sometimes occurs in subjects even when sickness was merely coincidental and not related to the food.
Operant conditioning, sometimes called instrumental conditioning or instrumental learning, was first extensively studied by Edward L. Thorndike (1874-1949). Thorndike's most famous work investigated the behavior of cats trying to escape from various home-made puzzle boxes. When first constrained in the boxes the cats took a long time to escape from each. With experience however, ineffective responses occurred less frequently and successful responses occurred more quickly enabling the cats to escape in less and less time over successive trials.
B.F. Skinner (1904-1990) extended the theories proposed by Thorndike about 40 years after Thorndike published his works. His ideas of animals operating on the environment, lead him to analyze how behavior is changed by its consequences. The contraption that became known has the Skinner box measured if a task was completed and the duration of time it took for the task to be completed. The Skinner box consisted of a bar on the wall that when pressed triggered the release of a food pellet. It was Skinners belief that by rewarding an animal when an appropriate action occurred it would increase the likelihood that the behavior would be repeated. When the rats, placed in the box, accidentally tapped on the bar on the wall a pellet was released and Skinner observed the amount of time it took the rat to find the pellet. As the rat learned that a pellet released each time he happened to step on the bar, the rat learned to press the bar and to immediately find the food. This training is what became known as operant conditioning . Reinforcement always strengthens the behavior that preceded it and may consist of any outcome that the animal considers desirable. Reinforcers can broadly be categorized into positive reinforcers (i.e., obtaining access to something the animal wants) or negative reinforcers (i.e., removing something considered unpleasant or painful). Punishment is always designed to discourage further performance of the behavior it is paired with. Positive punishment achieves that by inflicting an unwanted outcome such as unpleasant sounds or odors, electric shocks, or pain, while negative punishment removes access to something the animal wants. Skinners operant conditioning is seen in the learning behavior of many animals as well as humans. Oftentimes it goes completely unnoticed, but it can also be used as a deliberate tool in training. As young children explore their world and learn how to eliminate unpleasant stimuli and satisfy desires through proper behavior they are learning through operant conditioning.
Operant conditioning is used extensively in training animals towards performing quite complex tasks. Shaping involves the step-wise reinforcement of successive approximations. This training method relies on the animal to exhibit an interest in showing a wide range of behaviors as well as in obtaining rewards. When a desired behavior is performed, the trainer rewards this action. As this method relies on compliance from the animal, most suited to this training are a combination of positive reinforcers (e.g., a small item of food) for behavior compatible with the trainer's expectations, and negative punishment (e.g., withholding that food item) for behavior that is not. Initially rewards are issued for even a crude approximation or a component of the behavior. While these attempts may have earned the animal a reward at the beginning, subsequent rewards are contingent on progressively narrowing the behavior to what the trainer aims for.
Latent learning refers to an individual's ability to learn associations without explicit reinforcement. Exploratory behavior serves to acquire an understanding of the spatial relationships of objects. It includes the formation of “cognitive maps” of the surrounding. Daily success depends on knowldge of spatial relationships. Hummingbirds and bees recall the location and status of harvesting of flower resources, and several species of birds are able to track a large number of seed stores.
Bandura  illustrated the power of an instructional strategy in which children are allowed to observe behavior of individuals who are significant to them. Subsequently they are likely to imitate their role models especially when such behavior is reinforced. His work illustrates that observers readily adapt their behavior based on what they see around them, even when they received no encouragement or incentives to do so. Integrating a continuous interaction between behaviors, cognitions, and the environment, his social learning theory stresses the importance of observational learning, imitation, and modeling.
Humans show exceptional skill to communicate with fellow conspecific using verbal and gestural symbols. Such competence is arguably one of mankind's greatest assets as well as a key to most of our species' achievements. It brings us together with our peers and enriches us through an exchange of experiences, thoughts and value systems. It endows us with the means to acquire skills for situations that we may have never personally encountered before. A staggering range of regionally distinct languages and dialects, grouped in larger language families, not only serves as a system of communcation but also tags us for membership within a specific group. In addition to bringing us together, it has thereby been at the heart of an ancient source of division. Although few things in biology ever group cleanly into one of the nature vs. nurture extremes, this particular division seems to be purely cultural. Regardless of the specific race, ethnic or regional group that we happen to have joined through birth, we all are able to acquire competence in any human language. In particular, we seem to acquire our native language without formal education, long before many of our intellectual capabilities have mnatured, and simply by immersion into the particular language environment of parents and relatives during the first few years of our life. The scientific study of the nature and structure of languages is called linguistics.
Universal Grammar. BF Skinner (1957) suggested that infants learn language through a process described as operant conditioning, namely, via the monitoring and management of reward contingencies. Skinner's position would be that a four-term contingency analysis comprised of motivating operations, discriminative stimuli, responses and reinforcing stimuli would be the means by which behavior could be explained. In children and infants this process would be expanded by what he called "shaping", "prompting" and other stimuli modeling, imitation and reinforcing procedures. Language acquisition then is a process that would take thousands of instances of such training, and this appears largely to be what takes place. Critics who do not understand the inductive power of this approach largely assert that this view now "appears quite simplistic." However, this argument to complexity is not dissimilar to arguments against Darwin's theory of natural selection. How could the amazing complexity of the animal kingdom come about through such a simple means? Surely, we would need something more complex to explain the variety of animals? Darwin's theory of selection is now accepted as such a means, despite it's "apparent simplicity". Similarly the mechanism of operant conditioning can be seen as sufficient to account for very complex forms of behavior in a wide variety of circumstances without appealing to unproven, non-data driven speculative theoretical approaches like those of Noam Chomsky and others.
Language learning is clearly the most complex task any of us will ever undertake. Yet, the process appears to be considerably less painful than acquiring an understanding of calculus, or organic chemistry. Noam Chomsky (1975) has long argued that this paradox is best explained by the view that humans, and in particular children, have innate abilities that support the acquisition of a language. It is clear that we seem to be naturally good at it, especially before we reach puberty. Moreover, we appear to have a natural need to fill our world with language; in the absence of formal language tutoring a form of language structure develops anyway. Some say a specialized language faculty seems to aid in this process, one that includes innately specified constraints on what forms are possible. These innate, language-specific, information processing mechanisms may be encapsulated in language module of the brain. However, these innate faculties are inferred, hypothesized explanations with no foundation in fact. No biological location has been found for them, no genetic location, no brain structure. It is all inference.
All human languages, even spontaneous ones, show many common principles of language acquisition as well as rules of grammar. The concept of universal grammar proposes that this is due to a set of innate rules, which guide how we acquire language and how we construct valid sentences in it. It thus attempts to explain language in general, and not simply describe the construction of any one specific language per se.
There are many alternative theories of human language consistency besides the speculative theory of "universal grammar". One theory is that human environments possess common structures and human language simply responds to the commonality of the world. Universal grammar is a speculative, unproven hypothesis that is still awaiting confirmation and has no evidence to support it other than "rational argument".
Language Acquisition. At very young age, we acquire our native language by listening to, guessing at the meaning of, and imitating the symbols used by tutors around us. Moreover, during these early years we learn to walk and talk without any explicit need for understanding how we are doing what we are doing. In this process we seem to be helped by a set of Inherent learning strategies, the ability for optimized pattern perception of common, ambient symbols.
Infants are exceptionally broad in their abilities to perceive sound qualities. In fact, as infants we can distinguish many more language sounds than we can as adults. During the first year of life, infant brains are actively engaged in optimizing acoustic perception for the language sounds that surround them. Such early acquisition of information about native language depends on perceptually mapping both the critical aspects of language, and statistical properties of speech.
It is now clear that infants perceive the various phonetic units, track the frequency of different formants, and extract the boundaries of words from running speech. Patricia Kuhl  suggests that language acquisition is based on a combination of factors to provide a powerful discovery procedure for language. Evidence suggests that initial perception parses speech in a universal way in all human infants. Infants have inherent perceptual biases that segment phonetic units without providing innate descriptions of them. They were able to parse and discriminate a wide range of basic phonetic units. Adults, in contrast, are only able to discriminated phonetic units that occur in their first language, but fail to distinguish those that are not used there. Japanese adults, for example, fail to discriminate phonetic boundaries of r vs. l, boundaries that do not exist in Japanese. Such discrimination is based on general auditory processing mechanisms, rather than on innate phonetic feature detectors for speech. Language learning requires mapping these probabilistic patterns into language strategies. As infants detect frequency patterns in language input they identify higher-order units. Infants thus discover the critical parameters and phonetic dimensions of the sounds used in their native language. Sensory processing becomes optimized by experience for enhance perception of the specific language around them. Vocal learning unifies language perception and production where vocal learning depends on a comparison of one's own vocalizations to those of others. Imitation forms the integral bong between the perception and production of language abilities and together they become optimized for the first language. If a second language is learned later on, it will carry the accent typical for the speech motor patterns of their primary language, even following long-term instruction. Similarities in infant-directed speaking styles (increased pitch and exaggerated stress) enhances language learning by assisting infants in discriminating phonetic units, as well as by capturing attention.
Broca's Area underlies the ability to produce speech, but it is not critical for understanding language. Patients with damage will fail to form words properly, and speech is halting and slurred. Wermicke's Area is essential for the ability to understand language. Patients with damage to this area can speak clearly, but the words make no sense (i.e., word salad). The Arcuate Fasciculus connects these two areas. Damage to this connection causes conduction aphasia where language is understood, but neither can words be repeated, nor does own speech make any sense. Capabilities for speech are not distributed evenly across the two halfs of the brain. Speech is only disrupted when amobarbital is selectively used to anesthetize only the half of the brain which contains these speech centers. Imaging techniques (e.g. fMRI) have identified that bilingual individuals utilize an overlapping set of neurons in the language areas for these two languages. In contrast, individuals who have acquired a second language later in life will likely rely on separate neuronal areas in these speech centers. Late bilingual speakers are also less likely to show strong lateralization of speech function. This suggests that as two language systems are learned together early-on, they can share the same brain centers without causing catastrophic interference. In adult learning, the best sites of brain real estate have already been taken up by the first language, thus, any new language learning must coopt 'new' territory adjacent to it or on the other half of the brain.
Birds communicate information about danger, food, sex, group movements and many other purposes via acoutic signals. A subset of these have been termed song, as they frequently feature with extended, tonal, melodic characteristics. The Zebra Finch's song, for instance, includes several introductory notes followed by a string of syllables within an extended melodious pattern. Sonograms (i.e., a plot of the intensity of pitch against time) are commonly used as a primary tool for studying and comparing bird songs.
Respiratory muscles force streams of air from large air sacs through the bronchi. Membranes in the syrinx vibrate as air expressed from bronchi passes over them. Syrinx muscles for left and right sound producing structures can act independently, and many birds are able to sing harmonies with themselves. Song appears to play a role in advertising for sex and species recognition as song complexity frequently coincides with the presence of ornate plumage. It also stimulates and synchronizes courtship behavior, stimulates reproductive readiness in females, and contributes to pair bond maintenance. Local song dialects exist in many species.
Successful song in most adult male songbirds depends on memorizing the calls of a conspecific tutor during an earlier, sensitive phase in life. The appropriate song repertoire is acquired in a series of distinct stages. Young birds, during an early Sensory Phase, listen to a conspecific tutor and thereby obtain information about the characteristics of its own song. Only a very specific subset of surrounding songs is actually accepted as suitable, suggesting the presence of an in-built song template. Following this sensory phase, young birds actively begin to vocalize themselves. Their Subsong is an atonal, noisy, meaningless repetition of sounds, which lacks recognizable syllables. Akin to human Babbling birds practice coordinated movements of the respiratory system, sound producing organs, and related structures (e.g., tongue). During Sensory-motor Phase, young birds spontaneously produce Plastic Song, consisting of vocalizations with distinct syllables and recognizable elements. Such "work in progress" will include elements from the song of tutors and elaborate them into a variety of syllables and phrases that even exceed what eventually will be used in its adult song. The ability to hear its own vocalizations are critical for normal development. In transition to the Mature phase, birds adopt a Crystallized Song with syllables and syntax structure that is characteristic of its species. Once established, these song patterns remain fixed in many species, are no more disrupted by deafening, and are presented intact during each subsequent breeding season. In contrast open-ended learners (e.g. starlings and canaries) retain the capacity to adjust or alter their song throughout life.
Song production is under the control of multiple hormonal systems from embryonic gonads. Injections of testosterone induce adult males to sing, even out of season, while similar injections in females have no such effect. The presence of estrogen during male development appears to be essential. When estrogen is blocked experimentally in developing males, testosterone injections fail to elicit song. However, when estrogen had been delivered to developing females, injection of testosterone elicited song in them (Konishi).
Several neural centers with a role in song have been identified. The Higher Vocal Center (HVc) is a group of neurons in the forebrain that is larger in (singing) males than in (non-singing) females. Damage to it blocks song production in adults. The nucleus of the archistriatum (RA) in males is larger than in females and its neurons increase in size and dendritic arborization during song learning. Damage to this area blocks song production in adults. The lateral magnocellular nucleus of the anterior neostriatum (LMAN) is neither sexually dimorphic nor shows seasonal change in neuron size or number. Its ablation in young birds interferes with song acquisition but its ablation in adults brings about few deficits as long as song had already been been learned prior to damage. Area X of the paraolfactory lobe (Area X) is sexually dimorphic and new neurons are added in song learning. Damage to it interferes with song acquisition in young birds but not in adults.
As in every behavioral system, a series of independent questions can be addressed for song behavior in Zebra finches (Taeniopygia guttata).
- Proximate Causation: Zebra finch song production requires the flow of air through semi-independent vibrators in syrinx and vocal tract. The presence of song, and song repertoire size are reflected in sexual dimorphism of its controlling brain areas and nuclei. A learning pathway esists separate of a motor pathway. Singing, which is largely restricted to males, is under the control of androgens.
- Ultimate Causation: Song in Zebra finches is a learned vocalization used during courtship and defense of a territory. Advertising the individual's presence it serves to elicit mating opportunities from females and to stimulate the partner's reproductive behavior and physiology. Moreover, it functions to claim a territory and to repel competitors from it.
- Phylogeny: Virtually all 9000 species of birds have the ability to vocalize, including crows, turkeys, owls or nightingales. A large subset of them, including the zebra finch, are characterized by complex vocal organs, distinctive brain circuitry for song, and acquisition of species-characteristic vocalizations through learning. Taxonomically these are all restricted to a single order - the Passeriformes.
- Ontogeny: The emergence of adult zebra finch song illustrates the interactions of genetic and environmental factors in behavioral development. After periods of listening to the songs of tutors, starting its own partial vocalizations, rehearsing and adaptating its own song, the species-specific adult version slowly emerges. Song circuits exhibit extensive plasticity even in adults with ongoing neurogenesis and seasonal changes in neuronal morphology.
White-crowned sparrows (Zonotrichia leucophrys nuttalli) males sing a single song that shows considerable geographic variation in the form of stable dialects. Bilingual and blended strategies exist at the boundaries. The distinctiveness of the song depends on patterns of natal dispersal and the timing of learning. Subject to reinforcement by the song of neighbors, the system is highly dependent on auditory feedback. The work by Peter Marler, Doug Nelson and others for over 30 years illustrates how genetic and environmental factors interact during the development of a complex communication system. Males generally establish territories during late plastic song with a repertoire that consists of ~4 different songs. Improvisations yield individual-specific songs which closely match that of the nearest rival.
Cross-fostering experiments illustrate the role of auditory templates in song learning. Young birds reared in the presence of taped song will learn and present that song, even if the tape came from another species. A Song sparrow raised with a swamp sparrow tape will experience little difficulty to learn the swamp sparrow song. Birds in Isolation experiments are raised without access to intact adult song (i.e., no template) and will subsequently show deficiencies in their own song upon maturation. The song does nonetheless contain valid elements of intact adult song. Moreover, Deafening experiments, which deafen birds at hatching, results in song that still contains some valid elements but is an even cruder version than those of isolated birds. When Song preference experiments present young birds with a wide range of conspecific and heterospecific songs, they recognize and preferentially learn the song of its own species. Birds raised in Mixed syllables experiments in the presence of a mixture of swamp- and song sparrow syllables, will accurately produce these syllables in their song but lack the normal adult syntax.
Castration Experiments have shed light on the roles of hormones in song learning. Swamp sparrows that are castrated early in development have low testosterone levels compared to their male siblings. They acquire song but progress to plastic phase only. Treating such birds with injections of testosterone (Enhanced Testosterone Experiment) immediately crystallizes the song. Interfering with testosterone function in adult birds (Reduced Testosterone Experiment) degrades previously crystallized song back to plastic.
Brown-headed cowbirds (Molothrus ater) are gregarious birds that follows cattle herds. Brood parasites that are raised by parents of different species, no consistent, conspecific tutor available. So, how do they learn their own conspecific song? One of the strongest stimuli is the bird's own crystallized song and feedback from females is important (i.e., action-based learning).
Parallels between Bird Song and Human Speech LearningEdit
To learn their language, humans and white crowned sparrows follow similar steps, recognition, practice, and clarity. The best time for a human to learn their language is from toddler to twelve years old (Macdonald) and the best time for a white crowned sparrow to learn its song is between 10-50 days from when they were born. Both genes and environment play roles in determining the way each communicate.
The first step for humans and white crowned species in learning their language can be considered recognition. White crowned sparrows and humans listen to a tutor before they begin to communicate their language. The tutor teaches the language and the particular dialect, according to the area. Just like humans, the sparrows also have a dialect depending on where they live. A white crowned sparrow has certain genes that only allow them to learn its own species’ songs. Experiments have been performed in which the sparrow was kept in isolation and played tapes of other song sparrows, the white crowned sparrow will not imitate the other species’ song, but will sing an odd song unlike either species’ song. Humans also cannot communicate with each other using a different species’ language. A study was done in Avignon, France that observed children who were brought up by wolves. It was observed that the children spoke no language at all. Before studies of this kind were done it was thought that the children might learn to communicate with the wolves, just like the Tarzan story. This is not true, the children could not speak the human language nor the language of the wolves (Macdonald). It is a combination of environment and genes that tell white crowned sparrows and humans to learn their proper language. Genes tell the species to only learn the language of their own species and environment plays a factor in determining which dialect each will use.
Once the white crowned sparrow or infant has recognized its species, song, they can begin to practice the language. Infants first communicate by making sounds. The sounds can range from grunts to sounds that mimic their surrounding environments. For example, before babies can say words, they might say moo- moo when looking at a cow. After sounds come words. By the time the infant reaches one year, they should be making sentences out of words (Macdonald). The white crowned sparrow also does not immediately master its song. The sparrow will first sing a short subsong derived from the tutor’s full song. The sparrows keep practicing their subsong just as infants practice their words. After the sparrow has mastered its subsong it can start to form a full song. In both species it is necessary for them to hear themselves in order to vocalize their language correctly.
In conclusion, both white crowned sparrows first listen and recognize their particular species’ language. A white crowned sparrow has a tutor to teach the song. Infants usually have parents that teach them their verbal language. Then they must practice the language, starting off slow with sounds and building up. Both species will continue to improve and clarify their language throughout their lives.
Coordinated movement requires that motor neuron innervate one or more muscle cells with finely tuned neural patterning. For a person to perform even the simplest motor task, the activity of thousands of these motor units must be coordinated. It appears that the body handles this challenge by organizing motor units into modules of units whose activity is correlated. The cerebellum and basal ganglia are critical for motor learning. Motor learning is "relatively permanent", as the capability to respond appropriately is acquired and retained.
Memory, in its broadest sense, refers to an individual's ability to acquire information. The formation of memory traces is a complex task which all organisms appear to be able to do. Fundamentally, such an ability requires a series of distinct steps: Information must be encoded as meaningful associations are assessed, the resulting information must be stored in some form, and the memory record must be retrieved when needed. Humans exhibit little conscious awareness of mental processes, such as memory. These were thus long considered inaccessible to objective, scientific study. Inferences about the course of encoding, consolidation and storage of memory thus mostly rely on indirect methods such as testing for retrieval abilities. Consolidation of memory appears to involve independent paths at different time frames. Such evidence derives from the existence of different critical time frames for its formation, and its susceptibility to disruption with different pharmacological tools.
Sensory memory provides a means for organisms to remember the experience of a particular sensory perception after the stimulus itself has stopped. It thereby provides an immediate 'snapshot' of an animal's sensory experience. Sensory memory formation is involuntary and does not depend on attention. A different type of sensory memory is stored for each particular modality - Iconic memory is a fast decaying store of visual information that briefly stores an image which has been perceived for a small duration; Echoic memory is a fast decaying store of auditory information; Haptic memory is a type of sensory memory that represents touch stimuli. Details that prove significant are transferred to more permanent and conscious components of working memory. For example, a toddler who is burnt transfers information from tactile sensory memory to short term memory due to the significance of the stimulus.
Short-term memory allows the recall of something from several seconds to as long as a minute. Its strength does appear to depend primarily on attention and not rehearsal. It is thus highly vulnerable to disruption when attention shifts elsewhere. The amount of information that can be held is on the order of 4-6 numbers. This amount can be boosted by grouping them into distinct chunks as for telephone numbers (e.g., 202-456-1414). The ability to recall such information is contingent on transient patterns of neuronal activity in regions of the frontal and the parietal lobe. Memory of written language may primarily rely on acoustic components rather than visual ones, as we are much more likely to make mistakes between letters that sound similar (E,P,D) than those that have visual similarities (O, Q)
This type of memory, lasting hours to months, critically depends on a transfer of the information from short term memory using repeated rehearsal. The hippocampus appears to be an essential structure in such routing. Sleep is thought to improve the consolidation of information, possibly by hippocampal replaying of activity from the previous wake period. Electrical activation of hippocampal circuits reportedly are linked to feelings of Deja Vu.
Declarative (Explicit) MemoryEdit
Declarative memory refers to the ability to become conscious of, or declare, facts and experiences. It is also referred to as Explicit memory, when it involves direct recalling information that had been obtained from the external world. Representing knowledge of standard textbook material or events, it is best formed by actively recalling the material in spaced intervals. Compared to other forms or memory it is more volative; more easily formed and more easily forgotten. The primary neural basis appears to reside in the medial temporal lobe. Bilateral damage to this area results in anterograde amnesia, as in the famous case of the anonymus memory-impaired patient HM. A surgical procedure for epilepsy left him with damage to his brain in the medial temporal lobe on both sides. the hippocampal formation, parahippocampal gyrus, the entorhinal cortex, and the amygdala. He subsequently suffered from severe anterograde amnesia, where transfer of new events into long-term memory was impaired. He was unable to recall events once his attention had focused elsewhere. Semantic Memory is the ability to consciously recall knowledge of facts that are independent of a specific time and place. medial temporal lobe, diencephalon. Episodic Memory refers to the ability to explicitly recall information about a specific event that has occurred at a specific time and place, medial temporal lobe, diencephalon
Procedural (Implicit) MemoryEdit
Implicit memory, which does not need to involve conscious awareness in the act of recollection. Procedural Memory regards the learning of motor skills and habits. Formation requires repeated reinforcement, repetition and practice over many trials rather than recollection. Once formed it is less likely to be forgotten. It is also less easily transferred to related tasks than declarative learning. Striatum, basal ganglia, Deficits can be assessed using a serial reaction time (SRT) task, backwards reading, mirror drawing, probabilistic classification, artificial grammar learning, or prototype abstraction. Motor Responses with Classical Conditioning, Cerebellum. Emotional Responses with Fear conditioning involves an organism's ability to acquire fear responses to a previously neutral stimulus. This occurs when it becomes paired with an aversive stimulus, such as a shock or loud noise. James Watson's Little Albert experiment illustrated that children learned fear of objects when encounters with them were paired with loud noises. Priming refers to a context-dependent activations of clusters of neocortical neurons. As they become more activated, they are more likely to come into consciousness. Even reflex pathways are capable of surprising plasticity. For example, circuits that control motor patterns for walking will be subjected to optimization with sensory input.
months to lifetime
Patient HM suffered severe memory impairment following bilateral damage to his medial temporal lobes, hippocampal formation, parahippocampal gyrus, entorhinal cortex, and amygdala. His short-term memory remained intact, he was able to largely recall past events, and his ability to learn new motor skills was not disrupted. However, he suffered from severe anterograde amnesia, i.e., the ability to commit new events to long-term memory.
Memory mechainsms critically depend on changes in synaptic functioning. Hebb Synapses and their role in classical conditioning. If a synapse succeeds at driving a postsynaptic neuron above threshold, its subsequent effectiveness is strengthened.
Long-term potentiation is based on changes in neural signals which will potentiate a neural response for 1-2 weeks. potentiation involves increased release of the excitatory neurotransmitter glutamate.
Molecular changes at the synaptic levelEdit
During habituation, repeated stimulation of a sensory neuron leads to a smaller activation of the postsynaptic motor neuron. The primary cause for this is a progressive reduction of Ca++ inflow into the presynaptic terminal, decreased transmitter release, and a smaller activation of the postsynaptic target. In sensitization as a result of electrical head shock, release of serotonin activates second messenger systems and phosphorylation of key target molecules. Long-Term Memory depends on new protein synthesis and the formation of new synaptic connections.
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