Various factors contribute to SD in the modern world, and these include alcohol consumption, shifting work, exposure to excessive light and noise, stress, anxiety, and certain medical conditions. Insomnia, narcolepsy, restless leg syndrome, and obstructive sleep apnea are some of the manifestations of SD. It is experienced by many people to varying degrees. More than one-third of the global population suffers from insomnia, with prevalence rates ranging from 23.2% to 27.1% [1]. Additionally, the insomnia rate has increased to 29.7–58.4% during the epidemic [2]. Overall, the prevalence is higher in Asian and European regions, especially in East Asia, where it is about 27% ^[1][3][1,3]. In China, about 38% of the population suffers from various types of SD, and this rate is higher than the world average of 27%. Nearly half of older adults aged more than 60 years have experienced SD. More than a third of American adults have less than 6 h (h) of sleep per night. People with SD are more likely to develop diabetes, high blood pressure, heart disease, chronic kidney disease, and Alzheimer’s disease by up to two to three times more than those without SD [4]. Encoding, consolidation, and retrieval are the three stages of memory formation ^[5][6][5,6]. During sleep, memory functions, including spatial memory, memory recognition, long-term memory, short-term memory, and prospective memory, are maintained and strengthened. Several studies suggest that SD can decrease hippocampal activation during the encoding phase while in the awake period, resulting in impaired memory retrieval even after one night of recovery sleep [7]. Total SD negatively affects their ability to form trace-conditioned memories [8]. Memory has been shown to be highly affected by SD. As a result of SD, patients have varying degrees of impairment in their prospective and spatial memory ^{[9][10][11][12][13]}[9,10,11,12,13]. Memory impairment due to SD is a hot and difficult issue in current research. SD can result in memory impairment through a variety of mechanisms, but few studies have attempted to systematically and purposefully summarize the underlying mechanisms. Therefore, clarifying the substantive effect of SD on memory is extremely critical. A few studies reported that SD may improve memory, but others stated that SD increases the risk of various diseases and negatively affects learning and memory ^{[14][15][16][17]}[14,15,16,17].

Insomnia is the most prevalent type of sleep disorder and is characterized by a high rate of morbidity and mortality, as well as high social costs. A growing body of evidence suggests that sleep plays a critical role in memory because it is a normal physiological process and a crucial brain function [18]. Alzheimer’s disease, Parkinson’s disease, and dementia are all associated with SD. Several areas of the brain damaged by SD include the hippocampus, thalamus, prefrontal cortex, and anterior cingulate cortex (Figure 1). The hippocampus is responsible for the processing, consolidation, and retrieval of short- and long-term memory and for spatial navigation and orientation ^[6][19][6,19]. Proteins that are linked to the hippocampus are crucially involved in memory formation [20]. SD could induce damages to hippocampal neurons and reduce the size and volume of the hippocampus, impairing hippocampal-dependent memory functions and resulting in difficulties in recalling past events and forming new memories [21]. SD can affect hippocampal function at the molecular level by decreasing encoding-related activity within the hippocampus [22]. The thalamus is involved in regulating sleep–wake cycles during SD and emotional processing [23]. Similarly, SD can lead to decreased activity in the thalamus, resulting in impaired sensory perception and processing [24]. The encoding of working memory relies on the prefrontal cortex, which plays a crucial role in attention and memory ^[25][26][25,26]. Reduced prefrontal cortex activity caused by SD can impair cognitive function, including attention, working memory, and fear memory consolidation ^[27][28][27,28]. The anterior cingulate cortex modulates the frontoparietal functional connectivity between resting-state and working memory tasks [29]. Additionally, SD can cause decreased anterior cingulate cortex activity, leading to impaired emotional regulation and decision-making abilities ^[30][31][30,31]. Insomnia is often associated with a decline in memory function, indicating a strong connection between insomnia and memory loss.

SD has been reported to negatively affect memory in animal models and humans ^[32][33][32,33]. It can impair spatial working memory in humans [34], as well as in young rats after 24 h of SD [35]. SD with 4–6 weeks of chronic rapid eye movement sleep (REM) can affect hippocampal spatial memory, short-term memory, and long-term memory in Wister rats ^[36][37][38][36,37,38]. The induction of short- and long-term memory in Aplysia was inhibited by 9 h/12 h SD [39]. The short- and long-term memory was significantly impaired by SD in rats and sea rabbits ^[40][41][40,41]. Additionally, prospective memory and declarative memory are also affected by SD ^[13][42][13,42], resulting in attenuation of weakly encoded memories in humans [43] and impaired encoding of trace memory in rats [8]. Although SD has a great effect on the memory function of older individuals [44], healthy young men experienced impaired working memory after 16 h of total SD [45]. After total SD with multiplatform and mild stimulation, EPM-M1 male mice developed memory deficits in the plus-maze discriminative avoidance task and passive avoidance dance task. REM SD for 72 h impaired novelty-related object site memory in mice [46]. In a study using C57BL/6J mice, a mild stimulus method of SD was used to train them for 1 h on a location recognition task, which significantly impaired memory function after only 3 h [47]. When flies were exposed to 4 h of SD during the consolidation phase, their memory was disrupted [48]. Memory function is also impaired in Octodon degus [49] and zebrafish [50]. Multiple animal models demonstrated the effects of SD on memory. Memory processing is severely affected by acute or chronic SD (Table 1).