8Health 9 Acknowledgement: We thank Lin Lin who helped start behavioral tests in mice in the Jones lab 10 and Drs. C.E.L Stark and M.A. Yassa for allowing us to use software and materials they 11 developed.12 Abstract: 24 In temporal lobe epilepsy, the ability of the dentate gyrus to limit excitatory cortical input to the 25 hippocampus breaks down, leading to seizures. The dentate gyrus is also thought to help 26 discriminate between similar memories by performing pattern separation, but whether epilepsy 27 leads to a breakdown in this neural computation, and thus to mnemonic discrimination 28 impairments, remains unknown. Here we show that temporal lobe epilepsy is characterized by 29 behavioral deficits in mnemonic discrimination tasks, in both humans and mice. Using a recently 30 developed assay in brain slices of the same epileptic mice, we reveal a decreased ability of the 31 dentate gyrus to perform certain forms of pattern separation. This is due to a subset of granule 32 cells with abnormal bursting that can develop independently of early EEG abnormalities.
33Overall, our results linking physiology, computation and cognition in the same mice, advance 34 our understanding of episodic memory mechanisms and their dysfunction in epilepsy. 35 36 Keywords: 37 Patch-clamp, low-dose systemic kainate model, kainic acid, interictal spikes, novelty 38 recognition, firing rate, spiking patterns, similarity metrics, input-output, entorhinal cortex, 39 perforant path, EPSC, excitation/inhibition ratio, dentate gate, Hebb-Marr theory 40 41 Introduction: 42 Temporal lobe epilepsy (TLE) represents about 60% of all epilepsy cases, a third of 43 which are refractory to medication (Tellez-Zenteno and Hernandez-Ronquillo, 2012). TLE is 44DG neural pattern separation and 2) that such a failure causes mnemonic discrimination 87 impairments remain experimentally untested.
88Here we tested, in humans and mice, whether TLE is characterized by deficits in 89 mnemonic discrimination and then recorded, in brain slices from the same mice, the spiking 90 patterns of single GCs in response to parametrically varied afferent stimulation in order to gauge 91 neuronal pattern separation. 92 93 Materials and Methods: 94 Human Behavior. A mnemonic similarity task (Stark et al., 2019), also known as a 95 behavioral pattern separation (BPS) task (Stark et al., 2013), was administered to 15 patients in 96 the University of Wisconsin-Madison Epilepsy Monitoring Unit. Under an approved Institutional 97 Review Board protocol and after obtaining informed consent, the task was administered in 98 conjunction with a standard neuropsychiatric evaluation and during electroencephalographic 99 (EEG) recording, both of which are part of standard practice for diagnosing the patients' seizures. 100 Patients were 18-65 years old, male and female. Only patients with a preliminary diagnosis of 101 TLE were included in our analysis. As controls, 20 subjects without epilepsy, recruited to match 102 the patients' age and sex distributions (family members of ...
