Homeostatic regulation of long-term potentiation

Homeostasis is a key concept in biology. It enables ecosystems, organisms, organs and cells to adjust their operating range to values that ensure optimal performance. Homeostatic regulation of synaptic activity has been shown to play an important role during development. Here I investigated whether also mature neurons possess mechanisms to prevent the strengthening of input synapses once the limit of their ‘operating range’ has been reached. Using electrophysiological recordings in hippocampal slices, I showed that such a mechanism indeed exists but only comes into play after a considerable number of synapses has been potentiated. Thus, adult neurons can sustain a substantial amount of synaptic strengthening but, once a certain threshold of potentiation is exceeded, homeostatic regulation ensures that no further strengthening occurs

The neurobiology of Etruscan shrew active touch

The Etruscan shrew, Suncus etruscus, is not only the smallest terrestrial mammal, but also one of the fastest and most tactile hunters described to date. The shrew's skeletal muscle consists entirely of fast-twitch types and lacks slow fibres. Etruscan shrews detect, overwhelm, and kill insect prey in large numbers in darkness. The cricket prey is exquisitely mechanosensitive and fast-moving, and is as big as the shrew itself. Experiments with prey replica show that shape cues are both necessary and sufficient for evoking attacks. Shrew attacks are whisker guided by motion- and size-invariant Gestalt-like prey representations. Shrews often attack their prey prior to any signs of evasive manoeuvres. Shrews whisk at frequencies of approximately 14 Hz and can react with latencies as short as 25–30 ms to prey movement. The speed of attacks suggests that shrews identify and classify prey with a single touch. Large parts of the shrew's brain respond to vibrissal touch, which is represented in at least four cortical areas comprising collectively about a third of the cortical volume. Etruscan shrews can enter a torpid state and reduce their body temperature; we observed that cortical response latencies become two to three times longer when body temperature drops from 36°C to 24°C, suggesting that endothermy contributes to the animal's high-speed sensorimotor performance. We argue that small size, high-speed behaviour and extreme dependence on touch are not coincidental, but reflect an evolutionary strategy, in which the metabolic costs of small body size are outweighed by the advantages of being a short-range high-speed touch and kill predator