Evaluation of the taste using optical topography

The neural activity of the frontal lobe during ingestion of five basic tastants (substances that stimulate the sense of taste) was investigated in two subjects, a female in her twenties and a female in her forties by measuring oxidized hemoglobin concentrations (oxy-Hb) using a near-infrared spectroscopic topography (optical topography). When the same tastants were repeatedly ingested with the condition that the content was known by participants in advance, the oxy-Hb in the second test was higher than that in the first test and oxy-Hb in the third test was higher than that in the second test in most of the five tastants. Relation between preferences of the taste and oxy-Hb was investigated. Oxy-Hb ingesting tastants with favorite taste or unfavorite taste was higher than that ingesting moderate taste in the female in her twenties. However, in the female in her forties, with the increase in the preference of the taste, oxy-Hb increased in a stepwise manner. High oxy-Hb was seen always in the same place of the frontal lobe when ingesting sweet, salty and umami tastants. However, high oxy-Hb was seen in different places in the frontal lobe each time the participant ingested tastants such as sour or bitter. In an experiment of ingesting six different tastants successively, oxy-Hb levels were similar during the ingestion in a condition that the content was known by participants in advance while oxy-Hb levels fluctuated largely in ingesting these six tastants when the content was not known before the ingestion. From the results above, the neural activity during the ingestion of different kinds of tastants was influenced by many factors such as repetition of the ingestion, preference of the taste and perception of the tastants content in advance. These technics of measuring the neural activity in the frontal lobe during ingestion of tastants may be useful in development of new foodstuffs or food products, and nutrition counselling based on the information obtained by the near-infrared spectroscopic topography.