Potential role of monkey inferior parietal neurons coding action semantic equivalences as precursors of parts of speech

The anterior portion of the inferior parietal cortex possesses comprehensive representations of actions embedded in behavioural contexts. Mirror neurons, which respond to both self-executed and observed actions, exist in this brain region in addition to those originally found in the premotor cortex. We found that parietal mirror neurons responded differentially to identical actions embedded in different contexts. Another type of parietal mirror neuron represents an inverse and complementary property of responding equally to dissimilar actions made by itself and others for an identical purpose. Here, we propose a hypothesis that these sets of inferior parietal neurons constitute a neural basis for encoding the semantic equivalence of various actions across different agents and contexts. The neurons have mirror neuron properties, and they encoded generalization of agents, differentiation of outcomes, and categorization of actions that led to common functions. By integrating the activities of these mirror neurons with various codings, we further suggest that in the ancestral primates' brains, these various representations of meaningful action led to the gradual establishment of equivalence relations among the different types of actions, by sharing common action semantics. Such differential codings of the components of actions might represent precursors to the parts of protolanguage, such as gestural communication, which are shared among various members of a society. Finally, we suggest that the inferior parietal cortex serves as an interface between this action semantics system and other higher semantic systems, through common structures of action representation that mimic language syntax

Radiocarbon dating of wetland sediment from the Konsen Plateau, eastern Hokkaido, Japan

Highlights • Study of wetland sediment in the easternmost Asian monsoon affected region. • Sediment on the Konsen Plateau has continuously deposited since ∼4.0 ka. • C/N and C/S ratios suggest environmental changes during the late Holocene. Abstract Wetland soils are among the largest carbon reservoirs in terrestrial ecosystems and are vulnerable to climate change. Here we elucidate the developmental history of a wetland soil located on the Konsen Plateau in Hokkaido, Japan, during the Holocene. Through radiocarbon dating of sediment samples, we revealed that continuous sedimentation persisted over the past 4000 years. This onset of peat sedimentation was simultaneous with those reported in other wetlands in eastern Hokkaido. We hypothesized that cooling associated with the end of climatic optimal may have contributed to peat preservation. Elemental analyses also confirmed the formation of a stable wetland condition during the late Holocene. The C/N ratios were approximately 15–25 throughout the core, indicating that the organic materials in the sediments were steadily derived from terrestrial plants. The C/S ratios of the core varied between 43 and 97, suggesting that the sediments are free from marine influences. Our results provided continuous and stable record of wetland sedimentary environment in eastern Hokkaido over the past 4000 years