Thalamic burst firing--a neuronal code for temperature information$.

A total number of 840 neurons was extracellularly recorded from the rat's thalamus (ventrobasal complex, VB, and nucleus posterior, NPT) and from the midbrain (raphe nuclei, MB) while thermal stimuli were given to the hindlimbs, scrotal skin, and the tongue. Of all neurons found, 407 exhibited burst patterns; the highest percentage of burst cells was found in VB (50-85%) whereas only 1-015% of the NPt and MB neurons were burst cells. About one-half of all burst cells responded to peripheral temperature stimulation by changing their mean firing rate. The question dealt with in this paper is whether burst firing gives a more detailed information on thermal sensations than mean firing rate alone. Therefore, 40 burst cells (20 of which were thermo-responsive according to their mean firing rate) were further analyzed by evaluating several burst parameters such as burst frequency, number of spikes/burst and bursting index. However, when mean discharge rate did not respond to skin temperature, the burst parameters were not correlated with the stimulus, either. Hence it is concluded that the burst firing in the thalamic neurons investigated does not provide an additional detailed information of skin temperature.