As individuals grow older, a number of factors can reduce our cognitive (or thinking) abilities such as "normal" aging, neurodegenerative diseases, and cardiovascular disease. This study will evaluate whether cognitive rehabilitation and transcranial electrical stimulation (TES) can improve cognitive abilities. Cognitive rehabilitation refers to methods that are used to improve tasks people have trouble doing in everyday life. Transcranial electrical stimulation uses small amounts of electricity to try to alter brain functioning. These approaches may help improve cognitive abilities like attention, learning, memory, finding words, and problem solving as well as everyday functioning. The goal of this study is to identify how to best use these methods, either alone or in combination.

The primary objective of this study is to evaluate the feasibility of a neurorehabilitation treatment tailored to individual patient needs, with the ultimate goal of maximizing cognitive and real-world functioning for older adults with cognitive aging, mild cognitive impairment (MCI), neurodegenerative, or other neurological diseases/conditions.

Transcranial electrical stimulation (TES) is a non-invasive, neurorehabilitation procedure in which a weak electric current is passed between electrodes that are placed on the scalp with the intention of modulating excitability of the underlying brain regions. Because the field of TES is relatively young, rapidly evolving, and primarily focused on cognitive neuroscience with "healthy" individuals, there is a clear need for well-conceptualized and conducted clinical research. The current protocol is intentionally broad with respect to both methodology and patient characteristics in order to tailor potential TES interventions to individual patients or small samples. The current protocol utilizes various forms of TES including transcranial direct current stimulation (tDCS), alternating current stimulation (tACS), and random noise stimulation (tRNS) and sham stimulation in older adults. As this is a cross-over design, some participants may receive active (or "real") TES and/or sham TES conditions.This includes head to head comparisons of the different forms of TES. Additionally, TES could be performed in conjunction with cognitively-based intervention since this may enhance the neuroplastic response of the targeted brain region(s) while at the same time shaping/optimizing the pathways that are engaged by cognitively-based interventions. This broad approach is important since etiological differences in cognitive impairment may necessitate distinct interventions.

Inclusion Criteria:

1. Individuals who have reported cognitive dysfunction and cognitively intact participants.
2. Participants will be age 50 or older

Exclusion Criteria:

1. A history of epilepsy
2. Sensory or motor impairments that limit the ability to take part in the study
3. Current alcohol or drug abuse/dependence
4. Those who are currently pregnant or may become pregnant during the duration of the study (if there is a question of pregnancy, pregnancy tests will be available for participants at no charge)

Those who are being evaluated for TES methodology will also be excluded for 1) metallic or electronic implant 2) skull plates or other cranial implants that affect TES

Given the nature of this study, the participant, care provider, investigator, and/or outcome assessors may or may not be blinded to the treatment condition.