Discrimination of Verbal/Visuospatial Memory Retrieval Processes by Measuring Prefrontal Lobe Blood Volume with Functional Near-infrared Spectrometry

In cognitive task execution, retrieval processes transfer memories from long-term storage to working memory, comprising three short-term memories—phonological loop, visuospatial sketchpad, and episodic buffer—controlled by a short-term-memory central executive. The phonological loop and visuospatial sketchpad are prominent in verbal and visuospatial information processing, respectively. Individuals differ in how they retrieve the same information. Discrimination between verbal or visuospatial memory retrieval by monitoring central executive activation is useful. Functional near-infrared spectroscopy (fNIRS) was used to assess blood volume and prefrontal lobe brain activation. Using a novel approach, blood volume during memory retrieval was obtained using fNIRS. To eliminate other factors not related to the central executive activation, a base period was observed. Dynamic range was calculated for both memory retrieval and base periods, and differences obtained at ten positions within the prefrontal lobe were used as features to discriminate between verbal and visuospatial retrieval. For discrimination, k-nearest neighbor (kNN) and support vector machine (SVM) with different kernels were applied. Our method was tested on participants in verbal/visuospatial memory retrieval experiments. As the result, accuracy, positive predictive values, and negative predictive values of kNN and SVM were 1, which indicated that the proposed method successfully discriminated between verbal/visuospatial memory retrieval through prefrontal lobe blood volume observation.