Anisotropic connections in the cat midbrain tegmentum

Single unit responses of the cat midbrain tectum to stimuli applied through a microelectrode 500μ rostrally to the recording electrode were recorded extracellularly. The mean latency of both direct and monosynaptic responses was 0.3 msec greater than that for local microstimulation. The responses were identified from their latent and refractory periods, the presence of summation, and the dependence of the firing index on sodium glutamate application to the recorded neuron. Thresholds of synaptic responses were measured during vertical displacement of the stimulating electrode. The experimental relationships can be approximated by parabolic functions. The results indicate that rostrocaudal projections in the midbrain tegmentum are arranged horizontally.