Chromatin immunoprecipitation followed by sequencing (ChIP-seq) was carried out using established protocols1. Briefly, fresh frozen hippocampal tissue (both hemispheres) from each mouse (n=4 for each chow and keto diet) was finely minced on cold plate, crosslinked in 1% formaldehyde in PBS for 10 min at RT, then the reaction was quenched using 125 mM glycine for 5 min at RT. Crosslinked tissues were washed with ice-cold PBS. The pelleted tissue was suspended in Sucrose/ TKM buffer (0.25 M sucrose, 50 mM Tris-HCl (pH 7.5), 25 mM potassium chloride, 5 mM magnesium chloride, 1X Protease Inhibitors, 10 mM sodium butyrate) and subjected to dounce homogenization to isolate nuclei. The sample is centrifuged for 5 min at 5,000 g at 4C and the pelleted nuclei are resuspended in nuclei lysis buffer (10 mM Tris-HCl, pH 8, 100 mM NaCl, 1mM EDTA, 0.5 mM EGTA, 0.1 % sodium deoxycholate, 0.5% N-lauroylsarcosine). Chromatin was fragmented to approximately 250 bp using a Covaris E220 sonicator (used the following sonication settings: 150 Watts peak incident power, 13% duty factor, 200 cycles/burst, 20 min/sample (1200 sec/sample)). 0.1X volume of 10% Triton-X was added to the sonicated lysate to stabilize proteins. Equivalent quantities of sheared chromatin were incubated with Dynabeads-antibody complex and input control overnight at 4 °C with gentle rotation. For each sample, H3K4me antibody (Abcam, Cat. No. 8895) Dynabead complex was prepared.  Next day, the immunoprecipitated samples were washed with low salt buffer (0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl pH 8.0, 150 mM sodium chloride), high salt buffer (0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl pH 8.0, 500 mM sodium chloride), lithium chloride wash buffer (0.25 M lithium chloride, 1% CA-630, 1% sodium deoxycholate, 1 mM EDTA, 10 mM Tris-HCl pH 8.0) and 1X TE buffer (10 mM Tris-HCl pH 8.0, 1 mM EDTA). DNA was eluted from beads, crosslinks reversed, and DNA purified (QIAquick PCR Purification Kit Qiagen, Cat. No. 28106) together with input samples. The DNA was quantified using Qubit dsDNA high sensitivity assay kit (Cat. No. Q32851) and size distribution of DNA was assessed using an Agilent Bioanalyzer. 10ng of DNA was used for the library preperation. The enzymes and buffers used are from Qiagen Beverley, adapters & indexing primers are from IDT. DNA fragments were end-repaired to generate blunt ends, followed by the addition of a single adenosine (A) residue to the 3′ ends. Illumina sequencing adapters were then ligated to the DNA fragments. Size selection was performed using AMPure XP beads to enrich for fragments between 150 and 700 bp. Adapter-ligated fragments were amplified by PCR for 15 cycles using primers containing unique dual index sequences. The resulting libraries were sequenced on an Illumina NovaSeq X Plus platform using paired-end 150 bp reads.