Response of ventrobasal thalamic neurons activated by dorsal and dorsolateral funiculi: an intracellular study.

Intracellular responses to stimulation of the dorsal column (DC) and dorsolateral funiculus (DLF) were recorded in cells of the thalamic ventrobasal complex (VB) in anesthetized cats, with the dorsal funiculi either intact or isolated. The responsiveness of VB neurons was tested using graded stimulation, paired-shock, and interaction techniques. Of the 60 VB neurons thoroughly studied, 50 responded to stimulation of the DC with excitatory postsynaptic potentials (EPSPs) followed by inhibitory postsynaptic potentials (IPSPs); half of these 50 neurons responded to stimulation of the DLF with the same pattern, whereas no IPSPs could be elicited in the remaining neurons. The majority of EPSPs could be fractionated into unitary components during graded electrical stimulation. The number of such components observed was greater after DLF than after DC stimulation. In most neurons, the DLF-evoked EPSPs were smaller in amplitude than the DC-evoked EPSPs. Paired-shock stimulation facilitated the DLF excitatory responses. The amplitude of IPSPs induced by DLF stimulation was significantly smaller than that evoked by DC stimulation, and DC stimulation reduced the excitatory response to subsequent DLF stimulation. The data support the known dominance of the DC pathway in the cat.