Characteristics of midbrain respiratory neurons in sleep and wakefulness in the cat.

Midbrain neurons were recorded in sleep and wakefulness in chronic cats. In the first phase of this study, we attempted to detect respiratory neurons by observing neuronal activity on an oscilloscope and listening to it after audioamplification. We studied 780 neurons in this non-quantitative way and failed to detect any respiratory activity. In the second phase, 203 neurons were analyzed statistically: 15% of these had activity patterns significantly related to the respiratory cycle. In the third and final phase, we studied the details of the activity of midbrain respiratory neurons. Sixteen of 281 single neurons had discharge patterns significantly related to the respiratory cycle, but only 3 of the 16 were related to breathing with a consistency that essentially excluded the possibility of a false positive error. All 3 of these cells were only intermittently respiratory, and the intermittency varied from cell to cell and tended to depend upon the state of consciousness. These results differ substantially from reports that more than 30% of midbrain and diencephalic cells are respiratory neurons. The differences may be explained by the previous authors' use of a statistic, the respiratory nodulation index, that, as shown here and in a previous stimulation study, produces a large number of false positive errors.