The Depolarizing Action of GABA in Cultured Hippocampal Neurons Is Not Due to the Absence of Ketone Bodies

Two recent reports propose that the depolarizing action of GABA in the immature brain is an artifact of in vitro preparations in which glucose is the only energy source. The authors argue that this does not mimic the physiological environment because the suckling rats use ketone bodies and pyruvate as major sources of metabolic energy. Here, we show that availability of physiologically relevant levels of ketone bodies has no impact on the excitatory action of GABA in immature cultured hippocampal neurons. Addition of β-hydroxybutyrate (BHB), the primary ketone body in the neonate rat, affected neither intracellular calcium elevation nor membrane depolarizations induced by the GABA-A receptor agonist muscimol, when assessed with calcium imaging or perforated patch-clamp recording, respectively. These results confirm that the addition of ketone bodies to the extracellular environment to mimic conditions in the neonatal brain does not reverse the chloride gradient and therefore render GABA hyperpolarizing. Our data are consistent with the existence of a genuine “developmental switch” mechanism in which GABA goes from having a predominantly excitatory role in immature cells to a predominantly inhibitory one in adults

Uncanny but not confusing: Multisite study of perceptual category confusion in the Uncanny Valley

Android robots that resemble humans closely, but not perfectly, can provoke negative feelings of dislike and eeriness in humans (the “Uncanny Valley” effect). We investigated whether category confusion between the perceptual categories of “robot” and “human” contributes to Uncanny Valley aversion. Using a novel, validated corpus of 182 images of real robot and human faces, we precisely estimated the shape of the Uncanny Valley and the location of the perceived robot/human boundary. To implicitly measure confusion, we tracked 358 participants’ mouse trajectories as they categorized the faces. We observed a clear Uncanny Valley, though with some interesting differences from standard theoretical predictions; the initial apex of likability for highly mechanical robots indicated that these robots were still moderately dislikable, and the Uncanny Valley itself was positioned closer to the mechanical than to the human-like end of the spectrum. We also observed a pattern of categorization suggesting that humans do perceive a categorical robot/human boundary. Yet in contrast to predictions of the category confusion mechanism hypothesis, the locations of the Uncanny Valley and of the category boundary did not coincide, and mediation analyses further failed to support a mechanistic role of category confusion. These results suggest category confusion does not explain the Uncanny Valley effect