Fourier analysis of sinusoidally driven thalamocortical relay neurons and a minimal integrate-and-fire-or-burst model

We performed intracellular recordings of relay neurons from the lateral gen iculate nucleus of a cat thalamic slice preparation. We measured responses during both tonic and burst firing modes to sinusoidal current injection an d performed Fourier analysis on these responses. For comparison. we constru cted a minimal "integrate-and-fire-or-burst" (IFB) neuron model that reprod uces salient features of the relay cell responses. The IFB model is constra ined to quantitatively fit our Fourier analysis of experimental relay neuro n responses, including: the temporal tuning of the response in both tonic a nd burst modes, including a finding of low-pass and sometimes broadband beh avior of tonic firing and band-pass characteristics during bursting, and th e generally greater linearity of tonic compared with burst responses at low frequencies. In tonic mode, both experimental and theoretical responses di splay a frequency-dependent transition from massively superharmonic spiking to phase-locked superharmonic spiking near 3 Hz, followed by phase-locked subharmonic spiking at higher frequencies. Subharmonic and superharmonic bu rst responses also were observed experimentally. Characterizing the respons e properties of the "tuned" IFB model leads to insights regarding the obser ved stimulus dependence of burst versus tonic response mode in relay neuron s. Furthermore the simplicity of the IFB model makes it a candidate for lar ge scale network simulations of thalamic functioning.