ABSTRACT
Noninvasive modulation of cognitive brain functions with transcra-
nial low-level laser (or light) therapy (LLLT) is a novel and appealing
neurotherapeutic concept with many potential applications [1]. It
is supported by the groundbreaking discoveries of the beneficial
transcranial effects of infrared laser stimulation on higher-order
cortical functions such as attention, memory, and affective states.
Transcranial LLLT relies on low power density (mW/cm2) and
high energy density (J/cm2) monochromatic light in the red
to near-infrared wavelengths to modulate brain function in a
nondestructive and nonthermal manner. The proposed molecular
mechanism of action of transcranial LLLT is based on its effect on
the predominant endogenous neuronal photoacceptor cytochrome
oxidase, the terminal enzyme in themitochondrial respiratory chain.
This chapter presents evidence supporting our understanding of
the neurochemical, neurobiological, and brain network mechanisms
mediating observed cognitive effects in preclinical models and
humans. Primary neurochemical effects of transcranial LLLT are
defined as direct enzymatic effects occurring during effective
light stimulation that can be demonstrated in vitro and in vivo. Secondary neurobiological LLLT effects are long-lasting biological
effects occurring in vivo after light stimulation. Brain network mechanisms are higher-order neurophysiological effects produced
by the interaction of LLLT primary and secondary effects with
functional neuroanatomical networks that demand more metabolic
energy during a cognitive process. Key studies on LLLT-based
photoneuromodulation of mood and cognition as well as their
implications for future experimental and clinical applications are
also discussed.
