No abstract

Complex neuronal circuitries such as those present in the mammalian cerebral cortex have evolved as balanced networks of excitatory and inhibitory neurons. Although the establishment of appropriate numbers for these cells is essential for brain function and behaviour, our understanding of this fundamental process is very fragmentary. Here we show that interneuron cell survival in mice depends on the activity of pyramidal cells during a critical window of postnatal development, in which excitatory synaptic input to individual interneurons predicts their outcome. Pyramidal cells regulate interneuron survival through the negative modulation of PTEN signalling, which effectively drives interneuron cell death during this period. Taken together, our findings indicate that activity-dependent mechanisms dynamically adjust the number of inhibitory cells in nascent local cortical circuits, ultimately establishing the appropriate proportions of excitatory and inhibitory neurons in the cerebral cortex.

Psychophysiological studies of infants have found a relation between behavioral reactivity and indices of autonomic state. The relation between behavioral reactivity, assessed via maternal report, and autonomic state, assessed via cardiac vagal tone in 9-month-old infants was examined. Cardiac vagal tone was quantified by measuring the amplitude of respiratory sinus arrhythmia. High cardiac vagal tone was associated with greater behavioral reactivity, resulting in maternal reports of more difficult temperament. Stability of the two measures, cardiac vagal tone and difficult temperament, from 9 months to 3 years of age was demonstrated. In addition, 9-month cardiac vagal tone, independent of 9-month temperament, was related to 3-year difficultness with higher 9-month cardiac vagal tone being related to less-difficult 3-year behavior.

No abstract