Neural correlates of temporal presentness in the precuneus: a crosslinguistic fMRI study based on speech stimuli

Abstract

Abstracts 25The position of any event in time could be either present, past, or future. This temporal 26 discrimination is vitally important in our daily conversations, but it remains elusive how 27 the human brain distinguishes among the past, present, and future. To address this issue, 28 we searched for neural correlates of presentness, pastness, and futurity, each of which is 29 automatically evoked when we hear sentences such as 'it is raining now', 'it rained 30 yesterday', or 'it will rain tomorrow'. Here, we show that sentences that evoked 31 'presentness' activated the bilateral precuneus more strongly than those that evoked 32 'pastness' or 'futurity'. Interestingly, this contrast was shared across native speakers of 33 Japanese, English, and Chinese, languages which vary considerably in their verb tense 34 systems. The results suggest that the precuneus serves as a key region that provides the 35 origin, the Now, to our time perception irrespective of differences in tense systems 36 across languages. 37 38 Introduction 41Each position in time is either in the past, present, or future. This way of 42 discrimination in time, which McTaggart (McTaggart JE 1908) named the A series, is 43 essential in our daily conversation. When we hear someone saying "it looks like rain 44 today", for example, we are instantly aware that the speaker is addressing the weather in 45 the near future. If we say "it is raining in Osaka", the temporal position of the remark is 46 present. It is evident that the remark "it rained on and off all day" refers to the weather 47 some time in the past. Without reference to time in each remark, we are not able to 48 exchange comments on the weather. It is remarkable that the process of allocating each 49 rainy event to present, past, or future is so automatic that we cannot suppress a feeling 50 of "futurity" arising from the remark "it looks like rain". Which part of the brain 51 discriminates among "futurity", "presentness", and "pastness" without any conscious 52 effort? 53It is generally accepted that when we recall some events in the past, portions of 54 the memory system of the brain, such as the hippocampal and parahippocampal network 55 and the inferior frontal gyrus, are recruited (McClelland JL et al. 1995; Okuda J et al. 56 2003; Addis DR et al. 2007; Szpunar KK et al. 2007; Corkin S 2013; Wilson AG et al. 57 2013). Interestingly, similar regions are recruited when we consciously imagine some 58 events in the future (Maguire EA et al. 1998; Hassabis D and EA Maguire 2007; Addis 59 DR et al. 2011; Martin VC et al. 2011). These studies suggest that the memory system 60 supports our feelings of pastness as well as futurity. 61In a recent functional imaging study, Peer M et al. (2015) reported that the 62 precuneus, inferior parietal cortex, and medial frontal cortex are involved in mental 63 orientation in space, time, and person. These regions overlap with the default mode 64 4 network, one of a few basic cortical networks that are active even in a resting st...