The Blank Slate

Steven Pinker's book The Blank Slate argues that all humans are born with some innate traits. Here, Pinker talks about his thesis, and why some people found it incredibly upsetting.

Is Sleep Essential?

Is Sleep Essential?
Chiara Cirelli, Giulio Tononi
PLoS Biol 2008;6(8):e216.

Everybody knows that sleep is important, yet the function of sleep seems like the mythological phoenix: “Che vi sia ciascun lo dice, dove sia nessun lo sa” (“that there is one they all say, where it may be no one knows,” Wolfgang Amadeus Mozart and Lorenzo da Ponte [1790], Così fan tutte). But what if the search for an essential function of sleep is misguided? What if sleep is not required but rather a kind of extreme indolence that animals indulge in when they have no more pressing needs, such as eating or reproducing? In many circumstances sleeping may be a less dangerous choice than roaming around, wasting energy and exposing oneself to predators. Also, if sleep is just one out of a repertoire of available behaviors that is useful without being essential, it is easier to explain why sleep duration varies so much across species. This “null hypothesis” would explain why nobody has yet identified a core function of sleep. But how strong is the evidence supporting it? And are there counterexamples?

Reactivation of Single Neurons

Internally Generated Reactivation of Single Neurons in Human Hippocampus During Free Recall
Hagar Gelbard-Sagiv, Roy Mukamel, Michal Harel, Rafael Malach, Itzhak Fried
Science DOI: 10.1126/science.1164685

The emergence of memory, a trace of things past, into human consciousness is one of the greatest mysteries of the human mind. Whereas the neuronal basis of recognition memory can be probed experimentally in human and nonhuman primates, the study of free recall requires that the mind declare the occurrence of a recalled memory (an event intrinsic to the organism and invisible to an observer). Here, we report the activity of single neurons in the human hippocampus and surrounding areas when subjects first view television episodes consisting of audiovisual sequences and again later when they freely recall these episodes. A subset of these neurons exhibited selective firing, which often persisted throughout and following specific episodes for as long as 12 seconds. Verbal reports of memories of these specific episodes at the time of free recall were preceded by selective reactivation of the same hippocampal and entorhinal cortex neurons. We suggest that this reactivation is an internally generated neuronal correlate of the subjective experience of spontaneous emergence of human recollection.