Types of memory

Compare and contrast the four types of memory discussed in this week’s readings.

Memory is the result of learning and the new information acquired in the process; this can happen from a single exposure to an experience, or from repetitive information, actions, or experiences (Gazzaniga et al., 2019). The encoding, or processing of information, can happen at multiple stages. Acquisition usually occurs in the initial stages of processing, where sensory information is selected for further use and becomes utilized in short term or working memory (Gazzaniga et al., 2019). Consolidation is a type of encoding that typically happens when information is worked through short term memory and is passed along for future use; consolidation is the process of forming new neural connections, strengthening old connections, or modifying connections in order to accommodate new learning (Gazzaniga et al., 2019). Once memories are acquired and consolidated, they will be stored in various parts of the brain for safekeeping. If memories are stored correctly, they will be available for retrieval later and will provide the relevant information for making decisions or guiding behavior.

Sensory memory is the first type of memory, and the initial stage of processing sensory input from the various modalities into what will eventually become memories (Gazzaniga et al., 2019). Neural synapses, such as the optic synapse, can process a vast amount of raw information, but only some of the information is processed (Gazzaniga et al., 2019). The subcortical sensory systems hold onto the information for less than a second in what is known as the sensory buffer (Gazzaniga et al., 2019). During that brief time, the brain must decide what sensory information is relevant and disregard the rest in order to avoid processing bottlenecks. While sensory memory is not conscious, the selection of sensory information will often be impacted by selective attention and be geared toward gaining information needed for a goal-oriented behavior (Gazzaniga et al., 2019). Sensory memory is the ground floor for the formation of all further processing.
Short term memory, which consists of briefly held sensory information, both audio and visual, is used for the performance of executive functions using working memory (Gazzaniga et al., 2019). This is the second type of memory, and it is used consistently in every day decisions, behaviors, and as part of the memory encoding process. According to the working memory system of Baddeley and Hitch, working memory consists of a central executive mechanism that coordinates the manipulation and maintenance of the available visual and audio information (Gazzaniga et al., 2019). Portions of the lateral frontal and parietal lobe in the left hemisphere process and maintain audio information by performing a phonological loop; repeating the words, numbers, and any other audio input in order to maintain it in the short term memory (Carter et al., 2009). Portions of the inferolateral frontal cortex help maintain short term verbal memory, while the inferior frontal, posterior parietal, and extrastriate cortex in the occipital lobe bilaterally maintain spatial information for working memory (Carter et al., 2009). Much of this process is automatic, though one may have conscious awareness of the mental process involved in the executive function of their working memory. Ultimately, the central executive mechanism holds all of the necessary information it needs to perform a task. If the task or experience is repeated often, there will be an increased chance of it being encoded into long term memory.
Long term memory consists of two types of memory; declarative, or explicit memory, and nondeclarative, or implicit memory (Gazzaniga et al., 2019). The third type of memory is declarative memory, which is information that can be recalled consciously; this is divided further into two particular types of conscious memories. Episodic memories are memories about events or experiences, and are always recollections from the first person with context of the circumstances surrounding the event (Gazzaniga et al., 2019). Often, episodic memories contain multiple sensory perspectives such as what color the sky was or what kind of food was served at a party. Semantic memories are facts, dates, concepts and other general knowledge; this information is necessary for executive function, which relies on stored knowledge to guide behavior and logic (Gazzaniga et al., 2019). Knowing how to tell time or do algebra are both examples of semantic memories. The hippocampal memory structures, which are located in and around the medial temporal lobe, are critical for the transformation of experiences into new episodic and semantic memories (Carter et al., 2009). Patients without this portion of their brain, such as patient H.M., are unable to form new memories, a condition known as anterograde amnesia, yet are able to learn new procedural memories and retain old memories (Gazzaniga et al., 2019).
Non-declarative, or implicit memories, are not conscious memories and are the fourth type of memory. Non-declarative memories include procedural memories, conditioning responses, non-associated behaviors and perceptual priming (Gazzaniga et al., 2019). Procedural memories include actions like riding a bike, swimming, and reading, which require a lot of repetition and experience; once rehearsed enough, they become automatic behaviors that the brain can perform without conscious thought(Gazzaniga et al., 2019). Memory of learned skills is stored in the putamen (part of the basal ganglia), instinctive behaviors like defensive behavior and grooming are stored in the caudate nucleus (part of the dorsal striatum), and the movements like walking that require body skills and coordination are stored in the cerebellum as procedural memory (Carter et al., 2009). On a neural level, the neurons which fire together in various parts of the brain to perform an action such as picking up a fork are activated so many times that the synapses become stronger and the behavior becomes encoded into procedural memory (Gazzaniga et al., 2019).
Other nondeclarative memories include conditioned responses, non-associated behaviors and perceptual priming. Perceptual priming, on an implicit level, primes the brain to think about a concept, image, sound, or fact, which then increases accuracy with recognizing the same or similar stimulus at a later time (Gazzaniga et al., 2019). Research has shown that declarative and non-declarative memory operates on two different systems, allowing implicit responses from perceptual priming to occur without conscious knowledge or when there is damage to portions of the brain which control semantic memory (Gazzaniga et al., 2019). Conditioned responses, as well as non-associated behaviors like habituation and sensitization, are unconscious adjustments in behavior to a stimulus (Gazzaniga et al., 2019). A person may become conditioned to crave coffee every morning at 9 am, for example, or become habituated (or desensitized) to the sound of their car engine and therefore not notice it as they drive. Finally, sensitization is an adaptive behavior that would cause a person to shield their eyes from the sun, for example, in order to avoid harming themselves.

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