Cognitive neuroscience

Forgetting, reminding and remembering: the retrieval of lost spatial memory. de Hoz, L. et al. PLoS Biol. 2, 1233–1242 (2004)

An important question in the study of memory is whether retrograde amnesia represents a deficit in memory storage or retrieval. Rats with a partial lesion of the hippocampus, which prevented them from remembering the location of the platform in a water maze task, could be 'reminded' of the original location of the platform by an escape platform in another location. By distinguishing reminding from new place learning, this study shows that a disruption in retrieval can contribute to retrograde amnesia.

Neurological disorders

Preclinical vCJD after blood transfusion in a PRNP codon 129 heterozygous patient. Peden, A. H. et al. Lancet 364, 527–529 (2004)

The authors describe a patient who was found, at post-mortem, to have preclinical signs of vCJD (variant Creutzfeld–Jakob disease). The patient had received a blood transfusion 5 years previously from a donor who went on to develop vCJD. Although heterozygosity at codon 129 of the prion protein gene PRNP has been thought to protect against vCJD, this patient was heterozygous at codon 129. It might be that heterozygotes are not protected, but have a longer incubation period; alternatively, they might be vulnerable to infection but not to the disease.

Vision

Visual pattern recognition in Drosophila is invariant for retinal position. Tang, S. et al. Science 305, 1020–1022 (2004)

Translation invariance is the ability to recognize visual patterns independent of their retinal location. In previous studies, Drosophila melanogaster were unable to recognize patterns that were presented in a new region of the visual field. However, the stimulus features that were manipulated might have been occluded by vertical displacements of the stimuli. In this study, which used stimuli that varied in size and colour, flies showed pattern recognition independent of retinal position.

Cortical physiology

The contribution of spike threshold to the dichotomy of cortical simple and complex cells. Prieb, N. J. et al. Nature Neurosci. 29 August 2004 (10.1038/nn1310)

Simple and complex cells in the cat primary visual cortex are often distinguished by the ratio between modulated and unmodulated components of spike responses to drifting gratings. If the modulation ratio is taken from the subthreshold membrane potential instead of the spike rate, it is unimodally distributed. However, the nonlinear properties of the spike threshold, when applied to this distribution, define the two classes of neuron.