Table 2 Studies on improvement of cognitive dysfunction in AD patients after transcranial photobiomodulation

Maksimovich et al. (2015) [64]

AD patients (34.83% male and 65.17% female) without serious comorbidities

Visible region of spectrum;

20 mw, fiber diameter of 25–100 μm, 20–40 min

Transcatheterly

Improved cerebral microcirculation and cognitive recovery; decreased permanent dementia

Nichols et al. (2017) [62]

AD patients

1064 nm, 3.4 W, 250 mW/cm², 120 or 137.5 J/cm² per session, CW

Transcranially

Improved reaction time and lapses in psychomotor vigilance task and correct responses in delayed match to sample task; increased resting-state EEG alpha, beta, and gamma power;

Glushkovskaya et al

(2019) [24]

Mongrel male mice injected Aβ (1–42) peptide (1 μL, 200 μmol) in the

CA1 field of the hippocampus bilateral

1267 nm, 50–200 mW/cm², 18–39 J/cm² at brain’s surface, beam diameter of 5 mm, CW

Transcranially;

High power laser diode (LD-1267-FBG-350)

Transcranial photobiomodulation significantly reduces the deposition of Aβ plaques (by stimulating lymphatic drainage) and improves cognition, memory and neurological status

Xing et al. (2020) [72]

Double transgenic mice (APPswe/PSENdE9)

632.8 nm, 92 mW, 10 min, spot area of 0.785 cm² in cerebral cortex and hippocampus, once a day, CW

He–Ne laser

Transcranial photobiomodulation has the ability to improve cognitive impairment in Alzheimer’s disease

Shin et al. (2020) [73]

Transgenic (5XFAD) male mice

610 nm, 1.7 mW/cm², 2.0 J/cm², spot diameter of 4 mm onto the midpoint of the parietal bone and the posterior midline of the seventh cervical vertebra, 20 min × 3, 14 weeks

Skin-adherent LED probe

Transcranial photobiomodulation has the ability to reduce amyloid accumulation, neuronal loss and microgliosis and improve cognitive impairment by elevating insulin-degrading enzyme associated with Aβ degradation

Huang et al. (2021) [67]

AD patients with dementia but without serious comorbidities

1060–1080 nm and 15,000 mW, 23.1 mW/cm², ~ 650cm² per treatment area, 6 min × 2 daily for 8 weeks

Transcranially

(light treatment helmet devices)

The NIR light treatments demonstrated safety and positive cognitive improvements in AD patients with dementia, and the trial designed a simple treatment that could benefit dementia patients