Despite decades of research, Alzheimer’s Disease (AD) remains a lethal neurodegenerative disorder for which there are no effective treatments. This review examines the latest evidence of a novel and newly introduced perspective, which focuses on the restoration of gamma oscillations and investigates their potential role in the treatment of AD. Gamma brain activity (∼25–100 Hz) has been well-known for its role in cognitive function, including memory, and it is fundamental for healthy brain activity and intra-brain communication. Aberrant gamma oscillations have been observed in both mice AD models and human AD patients. A recent line of work demonstrated that gamma entrainment, through auditory and visual sensory stimulation, can effectively attenuate AD pathology and improve cognitive function in mice models of the disease. The first evidence from AD patients indicate that gamma entrainment therapy can reduce loss of functional connectivity and brain atrophy, improve cognitive function, and ameliorate several pathological markers of the disease. Even though research is still in its infancy, evidence suggests that gamma-based therapy may have a disease-modifying effect and has signified a new and promising era in AD research.

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Episodic memory decline is the prominent neuropsychological feature of typical Alzheimer's Disease (AD), for which current treatments have a limited clinical response. Recently, gamma entrainment therapy has been used as a non-invasive treatment in AD, providing evidence that it may have the potential to alleviate brain pathology and improve cognitive function in AD patients. At the same time, the precuneus (PC) has been recognized as a key area involved in AD related memory deficits and as a key node of the Default Mode Network. This study aimed to investigate the effectiveness of a 40 Hz Transcranial Magnetic Stimulation (TMS) intervention, delivered bilaterally to the precuneus for 10 days, in improving the patients' episodic memory performance. Secondary outcome variables investigated included general cognitive function, semantic and spatial memory, as well as attention and executive function. A concurrent multiple baseline design across five cases was employed. Four patients completed the study. Visual analysis combined with effect size indices were used to evaluate changes across phases. An increase in the average level of immediate recalled words was observed in three out of four patients. Effect size indices indicated significant improvement of attention skills in two patients. No treatment effect was observed for semantic and visual memory, or for executive function. An

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Visual short-term memory (VSTM) links perception with higher cognitive processes by maintaining visual information that is absent from the environment. Yet, it remains unclear if sensory visual cortex is a necessary component of the brain network that underlies short-term maintenance of visual information. Previous reviews remain inconclusive and open to interpretation. Here, we aimed to systematically identify and review studies that have investigated the role of the sensory visual cortex in VSTM using transcranial magnetic stimulation (TMS), a method that allows exploration of causal relationships, and to quantitatively explore the effect of TMS interference on the sensory visual cortex during VSTM using meta-analytic methodology. Thirteen studies were identified and qualitatively reviewed. Out of those, seven studies provided sufficient statistical data for meta-analysis and yielded a total of 30 effect sizes, which were included in the meta-analyses. Two meta-analyses were conducted, one regarding the encoding phase of VSTM (19 effect sizes), and one regarding the maintenance phase of VSTM (11 effect sizes). The results from the systematic review and the two meta-analyses indicate that the sensory visual cortex is likely involved in both the encoding and maintenance phase of VSTM. In some cases, evidence did not show significant effects of TMS, however, this is suggested to be due to low memory load or low perceptual task demands. Overall, these findings support the idea that sensory visual areas are part of the brain network responsible for successfully maintaining information in short-term memory when no physical stimulus is present in the environment.

Visual short-term memory (VSTM) links perception with higher cognitive processes by maintaining visual information that is absent from the environment. Yet, it remains unclear if sensory visual cortex is a necessary component of the brain network that underlies short-term maintenance of visual information. Previous reviews remain inconclusive and open to interpretation. Here, we aimed to systematically identify and review studies that have investigated the role of the sensory visual cortex in VSTM using transcranial magnetic stimulation (TMS), a method that allows exploration of causal relationships, and to quantitatively explore the effect of TMS interference on the sensory visual cortex during VSTM using meta-analytic methodology. Thirteen studies were identified and qualitatively reviewed. Out of those, seven studies provided sufficient statistical data for meta-analysis and yielded a total of 30 effect sizes, which were included in the meta-analyses. Two meta-analyses were conducted, one regarding the encoding phase of VSTM (19 effect sizes), and one regarding the maintenance phase of VSTM (11 effect sizes). The results from the systematic review and the two meta-analyses indicate that the sensory visual cortex is likely involved in both the encoding and maintenance phase of VSTM. In some cases, evidence did not show significant effects of TMS, however, this is suggested to be due to low memory load or low perceptual task demands. Overall, these findings support the idea that sensory visual areas are part of the brain network responsible for successfully maintaining information in short-term memory when no physical stimulus is present in the environment.

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