Does BDNF have pre- or postsynaptic targets?

A type of synaptic plasticity in the brain called long-term potentiation (LTP) is thought to form the molecular basis of learning and memory. In a Perspective, Manabe discusses new findings (Kovalchuk et al.) showing brain-derived neurotropic factor modulates LTP by binding to TrkB receptors on the postsynaptic neuron.     

Developmental behaviors: delayed appearance in monkeys asphyxiated at birth

In "Developmental behaviors: delayed appearance in monkeys asphyxiated at birth" by J. A. Sechzer et al. (19 Mar., p. 1173), the last two lines of column 1 and the first five lines of column 2, page 1175, should read "Deficits in learning and memory (10, 11) when compared with the establishment of these developmental behaviors (although significantly delayed) suggest that brain damage by neonatal asphyxia can result in a degree of dissociation..."     

Comment on "Tequila, a neurotrypsin ortholog, regulates long-term memory formation in Drosophila"

Didelot et al. (Reports, 11 August 2006, p. 851) claimed that Drosophila Tequila (Teq) and human neurotrypsin are orthologs and concluded that deficient long-term memory after Teq inactivation indicates that neurotrypsin plays its essential role for human cognitive functions through a similar mechanism. Our analyses suggest that Teq and neurotrypsin are not orthologous, leading us to question their equivalent roles in higher brain function.     

Comment on papers by Evans et al. and Mekel-Bobrov et al. on Evidence for Positive Selection of MCPH1 and ASPM

Evans et al. and Mekel-Bobrov et al. (Reports, 9 September 2005, p. 1717 and 1720, respectively) reported that human genetic variants of Microcephalin (MCPH1) and abnormal spindle-like microcephaly associated (ASPM) are under strong positive selection. We genotyped these variants in 9000 children and find no meaningful associations with brain size and various cognitive measures, which indicates that contrary to previous speculations, ASPM and MCPH1 have not been selected for brain-related effects.     

Neuroscience. From molecules to memory in the cerebellum

Neuroscientists have long sought to elucidate the molecular underpinnings of the memories needed to learn, for example, a motor task. In his Perspective, Linden discusses new work (Koekkoek et al.) suggesting that long-term depression in Purkinje cells mediated by protein kinase C signaling is responsible for motor memory in a task called associative eyelid conditioning.     

The prefrontal cortex: response selection or maintenance within working memory?

It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.     

Erratum

In the report "Selective protection of methionine enkephalin released from brain slices by enkephalinase inhibition" by G. Patey et al. (5 June, p. 1153), Fig. 1B was labeled incorrectly. The corrected figure is printed below.     

APPLIED PHYSICS: Smaller, Faster Midinfrared Lasers

Semiconductor lasers are small, efficient devices that are used widely as optical sources in telecommunication systems and CD-ROM and DVD optical memory drives. In his Perspective, Faist highlights the work by Paiella et al., who expand the range of operation of these devices substantially by demonstrating midinfrared lasers that emit picosecond pulses. Faist particularly stresses the innovative technique used by the authors, which may also allow new frequencies, for example in the terahertz frequency range, to be generated.     

Coupling between neuronal firing, field potentials, and FMRI in human auditory cortex

Functional magnetic resonance imaging (fMRI) is an important tool for investigating human brain function, but the relationship between the hemodynamically based fMRI signals in the human brain and the underlying neuronal activity is unclear. We recorded single unit activity and local field potentials in auditory cortex of two neurosurgical patients and compared them with the fMRI signals of 11 healthy subjects during presentation of an identical movie segment. The predicted fMRI signals derived from single units and the measured fMRI signals from auditory cortex showed a highly significant correlation (r = 0.75, P < 10(-47)). Thus, fMRI signals can provide a reliable measure of the firing rate of human cortical neurons.     

Comment on "Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens" and "Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans"

Mekel-Bobrov et al. and Evans et al. (Reports, 9 Sept. 2005, p. 1720 and p. 1717, respectively) examined sequence data from modern humans within two gene regions associated with brain development, ASPM and microcephalin, and concluded that selection of these genes must be ongoing. We show that models of human history that include both population growth and spatial structure can generate the observed patterns without selection.     

Effects of working-memory training on striatal dopamine release

Updating of working memory has been associated with striato-frontal brain regions and phasic dopaminergic neurotransmission. We assessed raclopride binding to striatal dopamine (DA) D2 receptors during a letter-updating task and a control condition before and after 5 weeks of updating training. Results showed that updating affected DA activity before training and that training further increased striatal DA release during updating. These findings highlight the pivotal role of transient neural processes associated with D2 receptor activity in working memory.     

Predicting human brain activity associated with the meanings of nouns

The question of how the human brain represents conceptual knowledge has been debated in many scientific fields. Brain imaging studies have shown that different spatial patterns of neural activation are associated with thinking about different semantic categories of pictures and words (for example, tools, buildings, and animals). We present a computational model that predicts the functional magnetic resonance imaging (fMRI) neural activation associated with words for which fMRI data are not yet available. This model is trained with a combination of data from a trillion-word text corpus and observed fMRI data associated with viewing several dozen concrete nouns. Once trained, the model predicts fMRI activation for thousands of other concrete nouns in the text corpus, with highly significant accuracies over the 60 nouns for which we currently have fMRI data.     

Erratum

In the report "Birth of projection neurons in adult avian brain may be related to perceptual or motor learning" by Arturo Alvarez-Buylla et al. (21 Sept., p. 1444), parts B and C in figure 1 were transposed. The legend is correct.     

Neuroscience. Feeling the pain of social loss

Poets have long waxed lyrical about the pain of a broken heart. Now, as Panksepp explains in his Perspective, this metaphor may reflect real events in the mammalian brain. A new brain neuroimaging study (Eisenberger et al.) reveals that the brain areas that are activated during the distress caused by social exclusion are also those activated during physical pain. Thus, we now have an explanation for the feeling of physical pain that accompanies emotional loss-whether that be the loss of a loved one, rejection by one's social group, or the distress of separation experienced by young animals.     

Protein kinase C overactivity impairs prefrontal cortical regulation of working memory

The prefrontal cortex is a higher brain region that regulates thought, behavior, and emotion using representational knowledge, operations often referred to as working memory. We tested the influence of protein kinase C (PKC) intracellular signaling on prefrontal cortical cognitive function and showed that high levels of PKC activity in prefrontal cortex, as seen for example during stress exposure, markedly impair behavioral and electrophysiological measures of working memory. These data suggest that excessive PKC activation can disrupt prefrontal cortical regulation of behavior and thought, possibly contributing to signs of prefrontal cortical dysfunction such as distractibility, impaired judgment, impulsivity, and thought disorder.     

Comment on "The Brain of LB1, Homo floresiensis"

Endocast analysis of the brain Homo floresiensis by Falk et al. (Reports, 8 April 2005, p. 242) implies that the hominid is an insular dwarf derived from H. erectus, but its tiny cranial capacity cannot result from normal dwarfing. Consideration of more appropriate microcephalic syndromes and specimens supports the hypothesis of modern human microcephaly.     

Comment on "Universality in the evolution of orientation columns in the visual cortex"

Kaschube et al. (Reports, 19 November 2010, p. 1113) argue that pinwheel density in three mammalian species follows a universal constant of π as predicted by their orientation-selective suppressive long-range connectivity model. We dispute their conclusions and suggest that a simple brain size-pinwheel density scaling law suffices in predicting the self-organized and disorganized orientation maps from primates to rodents.     

Erratum

In the Technical Comment "Trans-activator gene of HTLV-II: Interpretation" by W. C. Greene et al. (27 Feb., p. 1073), the third-from-the-last sentence should have read, "In addition, using Jurkat or other T-cell lines, Inoue and colleagues (2) and Maruyama et al. (3) have described activation of both the IL-2 receptor and IL-2 genes by the tat-I gene isolated from HTLV-I, which shares similar structural and functional properties with the tat-II gene." Reference 3 should have been to M. Maruyama et al., cell 48,343(1987).     

Neuroscience. More to seeing than meets the eye

A single event may elicit several different sensory stimuli such as vision, sound, and touch. But how does the brain know which of the many different stimuli arriving in the sensory cortex of the brain are connected? In her Perspective, de Gelder discusses new findings showing that when a touch is applied on the same side of the body as a visual cue, vision is enhanced (Macaluso et al.). She explains that this effect is due to neurons projecting from the somatosensory (touch) area of the sensory cortex back to the visual cortex. These neurons keep the visual cortex informed about tactile stimuli elicited at the same time as the visual stimuli.