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. Author manuscript; available in PMC: 2012 Jan 20.
Published in final edited form as: J Neurosci. 2011 Jul 20;31(29):10579–10592. doi: 10.1523/JNEUROSCI.1592-11.2011

Fig. 6. Combined LTP and LTD Changes Threshold Response with Minimal Gain Changes, while Parallel Fiber Rate Modulation Causes Significant Gain Changes.

Fig. 6

(Panel A illustrates experimental data, while the rest of Fig 6 illustrates modelling data). A. Measurement of gain in control and after combined LTP and LTD for 5 different fusiform cells (values were normalized to control: control: 100%; combined LTP and LTD: 95.8% ± 2.8% of control, p>0.05, the red trace represents the average response). Gain represents the slope of the response function around threshold. The slope was derived from experiments illustrated in 5D1, D2. B1. Fusiform cell model membrane potential (Vrest) (bottom) for different PF rates (top: control PF rate in black vs. lower PF rate in green). B2. Average resting model membrane potential (Vrest) for control (black) vs. lower PF rate (green). For comparison purposes combined LTP and LTD value is shown in red (same as in Fig. 4C1) B3. Average model input resistance Rm for the same conditions as (B2). For comparison purposes combined LTP and LTD values shown in red (same as in Fig. 4C2). C. Average model membrane response to an AN input in control (black trace) vs. PF rate modulation (green trace). Shaded areas are ± one standard deviation. D. Model fusiform cell response probability as a function of AN input strength (gAN) for different PF rates. E. The range of PF rates (top axis, green curve) that gave equivalent threshold shifts to the threshold shifts observed for the range of combined LTP and LTD modulation shown in Fig. 5B2 (bottom axis, red curve). F. Gain plotted as a function of threshold for combined LTP and LTD (red) and PF rate (green) modulation (dashed line indicates control values). G1. Schematic representation of input-output functions in the absence of membrane potential fluctuations. Weak synaptic primary inputs never reach spiking threshold (1), while strong inputs always elicit a spike (2). G2. Schematic representation of input-output function in the presence of membrane potential fluctuations. There is a graded response with increasing primary input strength. Note the emergence of a third response state (3) where spiking occurs with a probability between 0 and 1. H1. Membrane potential probability density function for control (black), for PF firing rate reduction (green) and for combined LTP and LTD (red). For comparison purposes the density functions were shifted so that they have identical mean values. H2. The variance of membrane potential fluctuations as a function of combined LTP and LTD (bottom axis, red curve) and PF rate modulation (top axis, green curve). The dashed line indicates control values. The range of combined LTP and LTD, and PF rate modulation are identical to that shown in E.