用神經功能術語來說，STM和LTM之間的區別是LTM中一係列事件的發生，這些事件必須確定地固定字母。這種作用是通過建立神經網絡而發生的，並表現為包括長期增強（LTP）在內的神經功能現象，這是由於突觸連接增強而引起的神經傳遞強度的增加。該過程需要基因表達和新蛋白的合成，並且與聲明性記憶的情況有關，涉及的大腦區域（如海馬體）的突觸（突觸合並）中的持久結構改變。海馬網絡的作用值得注意的是，海馬神經發生調節LTP的維持。但是，海馬網絡，包括海馬旁回，海馬和新皮層區域，並不是存儲記憶的地方，但在形成新記憶和隨後的激活中起著至關重要的作用。看起來海馬體的能力有限，無法長時間保持自動快速地自動獲取信息。隨著時間的推移，與海馬本身的活動無關，最初可獲得的信息在其他大腦結構（在皮層中）變得永久存在。這種轉移的關鍵機製是神經活動構型的重新激活（“重播”）。換句話說，海馬和與之相連的內側顳部結構對於整個事件的保存至關重要，因為它以一種有組織的方式分布在記憶中。它是一個操作係統，可以通過不同的軟件來存儲，組織，處理和恢複硬件文件。這種海馬引導的重新激活（檢索）導致在皮層痕跡之間直接建立連接，然後在新皮層中形成完整的表示，包括用於視覺記憶的視覺聯想皮層，用於聽覺記憶的顳皮層和左側側麵顳葉皮層用於單詞含義的知識。此外，海馬還有其他特定的任務，例如在空間記憶組織中。其他大腦區域也參與記憶過程。例如，運動技能的學習與小腦區和腦幹核的激活有關。此外，學習知覺活動（改善日常生活活動中必不可少的知覺刺激的過程，例如理解口語和書麵語言）涉及基底神經節以及感覺和聯想皮層，而學習認知技能（與解決問題有關）涉及最初是顳葉.
Short Term Memory Impairment
- PMID: 31424720
- NBK545136
Excerpt
Short-term memory (STM), also referred to as short-term storage, or primary or active memory indicates different systems of memory involved in the retention of pieces of information (memory chunks) for a relatively short time (usually up to 30 seconds). In contrast, long-term memory (LTM) may hold an indefinite amount of information. The difference between the two memories, however, is not just in the 'time' variable but is above all functional. Nevertheless, the two systems are closely related. Practically, STM works as a kind of “scratchpad” for temporary recall of a limited number of data (in the verbal domain, roughly the George Miller’s ‘magical’ number 7 +/- 2 items) that come from the sensory register and are ready to be processed through attention and recognition. On the other side, information collected in the LTM storage consist of memories for the performance of actions or skills (i.e., procedural memories, “knowing how”) and memories of facts, rules, concepts, and events (i.e., declarative memories, “knowing that”). Declarative memory includes semantic and episodic memory. The former concerns broad knowledge of facts, rules, concepts, and propositions ('general knowledge'), the latter is related to personal and experienced events and the contexts in which they occurred ('personal recollection'). Although STM is closely related to the concept of ‘working memory’ (WM), STM and WM represent two distinct entities. STM, indeed, is a set of storage systems whereas WM indicates the cognitive operations and executive functions associated with the organization and manipulation of stored information. Nevertheless, one hears the terms STM and WM often used interchangeably. Furthermore, one must distinguish STM from the ‘sensory memory’ (SM) such as the acoustical echoic and iconic visual memories which are shorter in duration (fraction of a second) than STM and reflect the original sensation, or perception, of the stimulus. In other words, SM is specific to the stimulus' modality of presentation. This ‘raw’ sensory information undergoes processing, and when it becomes STM gets expressed in a format different from that perceived initially. The famous Atkinson and Shiffrin model (or multi-store model), proposed in the late 1960s, explains the functional correlations between STM, LTM, SM, and WM. Later on, a considerable number of studies demonstrated the anatomical and functional distinction between memory processes as well as neural correlates and functioning of STM and LTM subsystems. In light of these findings, several memory models have been postulated. While certain authors suggested the existence of a single memory system encompassing both short- and long-term storage, after 50 years the Atkinson and Shiffrin model remains a valid approach for an explanation of the memory dynamics. In light of more recent research, however, the model has several problems mostly concerning the characteristics of STM, the relationship between STM and WM as well as the transition from STM to LTM. Short-term memory: meaning and system(s) It is a storage system that includes several subsystems with limited capacity. Rather than being a limitation, this restriction is an evolutionary survival advantage, since it allows paying attention to limited but essential information, excluding confounding factors. It is the classic example of the prey that must focus on the hostile environment to recognize a possible attack by the predator. Given the functional peculiarities of the STM (collection of sensorial information), the subsystems are closely related to the modalities of sensory memory. As a consequence, there have been several sensorial-associated subsystems postulated, including the visuospatial, phonological (auditory-verbal), tactile, and olfactory domains. These subsystems involve different patterns and functional interconnections with the corresponding cortical and subcortical areas and centers. The concept of working memory In 1974, Baddeley and Hitch developed an alternative model of STM which they termed as working memory. Indeed, the WM model does not exclude the modal model but enriches its contents. On the other side, the short-term store can be used to characterize the functioning of the WM. WM refers more to the entire theoretical framework of the structures and processes used for the storage and temporary manipulation of information, of which STM is only a component. In other words, STM is a functional storage element, while WM is a set of processes that also involve storage phases. WM It is the memory that we constantly use, which is always "online" when we have to understand something or solve a problem or make an argument, the cognitive strategies for achieving short term goals. The proof of the importance of this sort of 'operating system' of memory shows by the evidence that WM deficits are associated with several developmental disorders of learning, including attention-deficit hyperactivity disorder (ADHD), dyslexia, and specific language impairment (SLI). Short-term and Long-term memory These types of memory can be classically distinguished based on storage capacity and duration. The capacity of the STM, indeed, has limitations in the amount and duration of information it can maintain. In contrast, LTM features a seemingly unlimited capacity that can last years. The functional distinctions between systems of memory storing and the exact mechanisms for how memories transfer from ST to LTM remain a controversial issue. Do STM and LTM represent one or more systems with specific subsystems? Although the STM probably represents a sub-structure of the LTM, which is a sort of long-term activated storage, rather than looking for a 'physical' division, it seems appropriate to verify the mechanisms of transition from a memory that is only a passage to a lasting memory. Although the classic multi-modal model proposed that storage of ST memories occurs automatically without manipulation, the matter seems to be more involved. The phenomenon concerns quantitative (number of memories) and qualitative (quality of memory) features. Regarding quantitative data, although the number of Miller of 7 +/- 2 items identifies the number of elements included among individual slots, the grouping of memory bits into larger chunks (chunking) could allow storing a lot more information of bigger size and continuing to keep the magic number. The qualitative issue, or memory modulation within processing, is a fascinating phenomenon. It seems that the elements of STM undergo processing, which provides a sort of editing that involves the fragmentation of each element (chunking) and its re-elaboration and re-elaboration. This phase of memory processing is called encoding and can condition subsequent processing, including storage, and retrieval. The encoding process encompasses automatic (without conscious awareness) and effortful processing (through attention, practice, and thought) and allows us to retrieve information to be used to make decisions, answer questions, and so on. There are three pathways followed during the encoding step: the visual (information represented as a picture), acoustic (information represented as a sound), and semantic encoding (the meaning of the information). The processes interconnect with each other, so that information is broken down into different components. During recovery, the pathway that has produced the coding facilitates the recovery of the other components through a singular chain reaction. A particular perfume, for instance, makes us recall a specific episode or image. Of note, the encoding process affects the recovery, but the recovery itself undergoes a series of potential changes that can alter the initial content. In neurofunctional terms, the difference between STM and LTM is the occurrence, in the LTM, of a series of events that must fix the engram(s) definitively. This effect occurs through the establishment of neural networks and expresses as neurofunctional phenomena including the long term potentiation (LTP) which is an increase in the strength of the neural transmission deriving from the strengthening of synaptic connections. This process requires gene expression and the synthesis of new proteins and is related to long-lasting structural alterations in the synapses (synaptic consolidation) of the brain areas involved such as the hippocampus is the case of declarative memories. The role of the hippocampal network Of note, the hippocampal neurogenesis regulates the maintenance of LTP. However, the hippocampal network, including the parahippocampal gyrus, hippocampus, and neocortical areas is not the place where memories are stored, but it has a crucial role in forming new memories and in their subsequent reactivation. It seems that the hippocampus has a limited capacity and acquires information quickly and automatically without keeping it for long. Over time, the originally available information becomes permanent in other brain structures (in the cortex), independently from the activity of the hippocampus itself. The crucial mechanism of this transfer is the reactivation ("replay") of the configurations of neural activity. In other words, the hippocampus and the medial temporal structures connected to it are crucial for holding an event as a whole as it distributes in an organized way memory traces. It is an operating system that through different software can store, organize, process, and recover hardware files. This hippocampal-guided reactivation (retrieval) leads to the creation of direct connections between the cortical traces and then to the formation of an integrated representation in the neocortex including the visual association cortex for visual memory, the temporal cortex for auditory memory, and the left lateral temporal cortex for knowledge of word meaning. Moreover, the hippocampus has other specific tasks, for example, in the spatial memory organization. Other brain areas are involved in memory processes; for example, the learning of motor skills has links to the activation of the cerebellar regions and brainstem nuclei. Furthermore, learning of perceptive activities (improvements in the processing of perceptive stimuli essential in everyday life activities such as understand spoken and written language) involves, basal ganglia and sensory and associative cortices whereas learning cognitive skills (related to problem-solving) involve the medial temporal lobes initially.
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