Neuromodulation

A rapid switch in sympathetic neurotransmitter release properties mediated by the p75 receptor.Yang, B. et al. Nature Neurosci. 5, 539–545 (2002)

Neonatal sympathetic neurons that innervate cardiac myocytes in culture contain both an inhibitory neurotransmitter, acetylcholine, and an excitatory one, noradrenaline. Yang et al. show that brain-derived neurotrophic factor, acting through the p75 neurotrophin receptor, causes cultured sympathetic neurons to switch from excitatory to inhibitory transmission within a short space of time.

Motor systems

Complex movements evoked by microstimulation of precentral cortex.Graziano, M. S. A. et al. Neuron 34, 841–851 (2002)

The authors stimulated discrete points of the motor and premotor cortices, and managed to elicit complex movement sequences that involved many joints. The effect of the stimulation at any given point was reproducible; it always led to the same final posture regardless of the direction of movement that was required to reach that position. Furthermore, postures that involved the upper limb formed a topographic map of hand positions around the body, providing evidence that motor and premotor areas contain an egocentric workspace map.

Learning and memory

The basolateral complex of the amygdala is necessary for acquisition but not expression of CS motivational value in appetitive Pavlovian second-order conditioning.Setlow, B. et al. Eur. J. Neurosci. (in the press)

In Pavlovian conditioning, a rat can be taught to associate a conditioned stimulus (CS) with a food reward — this is known as first-order conditioning. In second-order conditioning, the initial CS is paired with a new CS in the absence of food, and the rat learns to expect food on presentation of the new CS. Here, the authors show that the basolateral complex of the amygdala is required for learning the motivational value of the initial CS, but not to maintain this information or to form the second-order association.

Vision

Aware or unaware: assessment of cortical blindness in four men and a monkey.Stoerig, P. et al. Cereb. Cortex 12, 565–574 (2002)

People with blindsight can see, but they are not consciously aware of it. Testing for conscious vision in humans requires them to say whether they saw a stimulus, so it is difficult to distinguish blindsight from residual conscious vision in animals. Here, Stoerig et al. trained a hemianopic monkey to indicate when she failed to detect a stimulus, and they ascertained that her blindness was due to loss of conscious vision. This constitutes the first evidence that blindsight can be modelled in primates.