Spatiotemporal dynamics of long-term potentiation in rat insular cortex revealed by optical imaging

Long-term potentiation (LTP) of the gustatory cortex (GC), a part of the insular cortex (IC) around the middle cerebral artery, is a key process of gustatory learning and memory, including conditioned taste aversion learning. The rostral (rGC) and caudal GC (cGC) process different tastes; the rGC responds to hedonic and the cGC responds to aversive tastes. However, plastic changes of spatial interaction of excitatory propagation between the rGC and cGC remain unknown. The present study aimed to elucidate spatiotemporal profiles of excitatory propagation, induced by electrical stimulation (five train pulses) of the rGC/cGC before and after LTP induction, using in vivo optical imaging with a voltage-sensitive dye. We demonstrated that tetanic stimulation of the cGC induced long-lasting expansion of the excitation responding to five train stimulation of the cGC, and an increase in amplitude of optical signals in the IC. Excitatory propagation after LTP induction spread preferentially toward the rostral IC: the length constant (λ) of excitation, obtained by fitting optical signals with a monoexponential curve, was increased to 121.9% in the rostral direction, whereas λ for the caudal, dorsal, and ventral directions were 48.9%, 44.2%, and 62.5%, respectively. LTP induction was prevented by pre-application of D-APV, an NMDA receptor antagonist, or atropine, a muscarinic receptor antagonist, to the cortical surface. In contrast, rGC stimulation induced only slight LTP without direction preference. Considering the different roles of the rGC and cGC in gustatory processing, these characteristic patterns of LTP in the GC may be involved in a mechanism underlying conversion of palatability.     

A new "fat face" illusion

We report a novel fat face illusion that when two identical images of the same face are aligned vertically, the face at the bottom appears 'fatter'. This illusion emerged when the faces were shown upright, but not inverted, with the size of the illusion being 4%. When the faces were presented upside down, the illusion did not emerge. Also, when upright clocks were shown in the same vertically aligned fashion, we did not observe the illusion, indicating that the fat illusion does not generalize to every category of canonically upright objects with similar geometric shape as a face.     

Individuality of Narratives Generated by Individuals: An Investigation Using Four-Panel Comics

In this study, we conducted an empirical research focusing on the generation of stories to obtain a hypothesis on how different the stories that people generate in their daily lives by linking events and situations are. For this purpose, five illustrations that revealed only the first and fourth panels of a four-panel comic were used as stimuli to generate a narrative in which the participants could make a connection between them. A total of 40 stories were obtained from eight participants. As a result, the narrative emerged in a variety of ways, even in events with little personal connection to the participants. This reveals that there are individual differences in the way people generate narratives themselves, despite their relationship with and position on the event. When the stories were typified, none of the participants generated similar stories in all five illustrations. This suggests that, because the combination of stories a person creates about every event is unique, there is only one story about the world, and one about himself/herself.