Abstract
Here we use computational modeling to gain new insights into the transformation of inputs in hippocampal field CA1. We considered input-output transformation in CA1 principal cells of the rat hippocampus, with activity synchronized by population gamma oscillations. Prior experiments have shown that such synchronization is especially strong for cells within one millimeter of each other. We therefore simulated a one-millimeter patch of CA1 with 23,500 principal cells. We used morphologically and biophysically detailed neuronal models, each with more than 1000 compartments and thousands of synaptic inputs. Inputs came from binary patterns of spiking neurons from field CA3 and entorhinal cortex (EC). On average, each presynaptic pattern initiated action potentials in the same number of CA1 principal cells in the patch. We considered pairs of similar and pairs of distinct patterns. In all the cases CA1 strongly separated input patterns. However, CA1 cells were considerably more sensitive to small alterations in EC patterns compared to CA3 patterns. Our results can be used for comparison of input-to-output transformations in normal and pathological hippocampal networks.
Highlights
Normal hippocampal functioning is essential for learning and memory
We adjusted presynaptic activity to conform to the results of Brun et al (2002, 2008). These studies showed that CA1 place cells have a peak firing rate of about 7 Hz with only CA3 inputs or only entorhinal cortex (EC) inputs, corresponding to a ∼14% probability of action potential initiation (API) during a 20 ms gamma period
To find the level of presynaptic activity resulting in 14% API probability in CA1 principal cells we calculated CA1 outputs for multiple levels of CA3 and EC activity (Figure 3)
Summary
Normal hippocampal functioning is essential for learning and memory. Abnormalities of the hippocampus are associated with the cognitive symptoms of schizophrenia, Alzheimer disease and other disorders (Disterhoft et al, 2004; Walker et al, 2006; Schobel et al, 2009). Hippocampal information processing and its contribution to cognitive symptoms has been described using several animal and computer models: learning and reproducing sequences of stimuli (Hasselmo et al, 2002; Gluck et al, 2003; Cutsuridis et al, 2010), properties of place fields in rodents (Olypher et al, 2006), generation of population rhythms, such as gamma oscillations, associated with cognitive processes (Neymotin et al, 2011; Volman et al, 2011), and information transmission in the hippocampus, in particular from the hippocampal field CA3 and entorhinal cortex (EC) to CA1 (Treves and Rolls, 1994; Schultz and Rolls, 1999). In contrast to classical estimates of information transmission as for example in Treves and Rolls (1994), our approach does not involve characterization of ensemble probabilities of spiking distributions in presynaptic and postsynaptic networks
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