Preparation of Acute Human Neocortical Slices

All procedures on human tissue were performed with the approval of the Medical Ethical Committee of the VU University Medical Center and in accordance with Dutch licence procedures and the Declaration of Helsinki. Human slices were cut from anterior medial temporal cortex that had to be removed for the surgical treatment of deeper brain structures for epilepsy or tumors with written informed consent of the patients (aged 18–61 years) prior to surgery. Anaesthesia was induced with intravenous fentanyl 1–3 µg/kg and a bolus dose of propofol (2–10 mg/kg) and was maintained with remyfentanyl 250 µg/kg/min and propofol 4–12 mg/kg. Immediately following removal from the brain, neuropathologists assessed whether it was normal or diseased tissue and only those samples that were designated as normal were used in the present study.
After resection, the neocortical tissue was placed within 30 seconds in ice-cold artificial cerebrospinal fluid (aCSF) slicing solution which contained in (mM): 110 choline chloride, 26 NaHCO₃, 10 D-glucose, 11.6 sodium ascorbate, 7 MgCl₂, 3.1 sodium pyruvate, 2.5 KCl, 1.25 NaH₂PO₄, and 0.5 CaCl₂ (300 mOsm) [23] (link),[24] (link),[45] (link) and transported to the neurophysiology laboratory, which is located within 500 m from the operating room. The transition time between resection of the tissue and the start of preparing slices was less than 15 minutes.
Neocortical slices (350–400 µm thickness) were prepared in ice-cold slicing solution, and were then transferred to holding chambers in which they were stored for 30 minutes at 34°C and for 30 minutes at room temperature before recording in aCSF, which contained (in mM): 126 NaCl; 3 KCl; 1 NaH₂PO₄; 1 MgSO₄; 2 CaCl₂; 26 NaHCO₃; 10 glucose (300 mOsm), bubbled with carbogen gas (95% O₂/5% CO₂).