Can Low-level Light Therapy Boost Memory?

Megan Brooks

December 07, 2012

Low-level light therapy (LLLT) with red to near-infrared light-emitting diodes (LEDs) enhances cortical oxygenation and metabolic capacity and memory retention, scientists observed in a series of animal experiments.

Because cerebral hypometabolism characterizes mild cognitive impairment, they say transcranially applied LLLT could have memory-enhancing effects in humans.

The ability of LLLT to increase mitochondrial energy metabolism could be used to recover brain processes affected by regional brain hypometabolism associated with Alzheimer's disease (AD), Francisco Gonzalez-Lima, PhD, University of Austin, Texas, and colleagues suggest.

"Furthermore, LLLT could be used as a preventive intervention in people who present risk factors for AD, such as those with chronic cerebrovascular hypoperfusion, mild cognitive impairment, or a history of head trauma. In such patients, LLLT could be combined with cognitive intervention approaches," they say.

Their study is published online in the Journal of Alzheimer's Disease.

Light Modulates Neuronal Function

Growing evidence supports that neuronal metabolic enhancement by LLLT positively affects neuronal function in vitro and in vivo. On the basis of its effects on energy metabolism, it's thought that LLLT will also affect the cerebral cortex in vivo and modulate higher-order cognitive functions such as memory. Yet, data are lacking on the in vivo effects of LLLT on brain and behavior.

In 4 separate experiments in rats, the Texas team tested the hypothesis that in vivo LLLT to the head facilitates cortical oxygenation and metabolic energy capacity and thereby improves memory retention.

Experiment 1, they say, "verified" that exposure to LLLT increased the rate of oxygen consumption in the prefrontal cortex in the animals.

In experiment 2, they observed that LLLT, compared with no therapy, was able to facilitate or enhance "fear extinction" memory, a form of memory modulated by prefrontal cortex activation. Experiment 3 showed that providing LLLT after extinction prevented a reemergence of fear responses. Experiment 4 showed that LLLT increased the metabolic capacity of the prefrontal cortex.

The researchers say this study is "the first demonstration that LLLT can improve extinction memory." It also provides evidence that both primary and secondary LLLT effects occur in the brain in vivo.

'Promising' Neurotherapeutic Tool

Experiments in humans have also demonstrated changes in frontal cortex regional cerebral blood flow after exposure to LLLT in the forehead, the researchers say.

Research has also shown beneficial effects of LLLT on cognition. For example, 1 study in middle-aged mice found improvements in working memory after LLLT. Another study reported that daily use of LLLT to the head was associated with improvement in attention, executive function, and memory in 2 patients with chronic traumatic brain injury.

"Reports in rats and humans provide further evidence that LLLT modulates mood and decreases depressive symptoms," the researchers say.

"Taken together, the data supports that LLLT to the head constitutes a promising neurotherapeutic tool to modulate behavior in a non-invasive manner. Future projects should determine the effects of variation in LLLT parameters such as wavelength, radiant exposure, irradiance, and wave type on transcranial applications to affect behavioral and brain metabolic variables," they write.

The study was supported by the National Institutes of Health. The authors have disclosed no relevant financial relationships.

J Alzheimers Dis. 2012;32:741-752. Abstract