The purpose of this study was to analyze participants' levels of hemoglobin as they performed arithmetic mental calculations using Optical Topography (OT, helmet type brain-scanning system, also known as Functional Near-Infrared Spectroscopy or fNIRS). A central issue in cognitive neuroscience involves the study of how the human brain encodes and manipulates information, including mental calculation. Recently, functional neuro-imaging studies have begun to clarify how the human brain performs mental calculations. fNIRS is an imaging technique capable of measuring changes in the relative concentration of hemoglobin the in the cerebral cortex of the brain (Hoshi & Tamura, 1993; Villringer et al., 1993; Koizumi et al., 2003). It is well known that near-infrared light of a wavelength between 650 nm and 950 nm can penetrate living tissue where it is specifically absorbed by hemoglobin (Strangman et al., 2002). By illumination the surface of the brain with near-infrared light of two specific wavelengths (695 nm for deoxy- and 830 nm for the oxygen-carrying oxyhemoglobin) changes in the concentrations of oxy- and deoxyhemoglobin can be monitored and allow conclusions about the energy consumption, or activation of the brain region during the performance of cognitive tasks. Twelve undergraduate and graduate college-level students participated in scanning session. Differences in brain activity were found based on mental calculation strategies. There were there different levels of oxy-hemoglobin: low, moderate, and high. The levels of activity were related to participants' mental strategies as they solve the exercises. Students who used more rote memorization tended to show moderate to low hemoglobin oxygenation. These results may have implications for how important rote memorization of arithmetic facts might be. Other results and possible implications are discussed in this article. (Contains 6 tables and 22 figures.)