that part of the brain that senses danger, where instincts and gut feelings originate; primal thoughts; subconscious or involuntary processes; the amygdala
"Dexter" Season 5, Episode 7:
Lumen: I just had a feeling. Some sort of lizard brain thing.
Dexter: She's starting to sound like me.

"Dexter" Season 7, Episode 3:
Deb: How do you know he'll kill again?
Dexter: An alarm is going off inside my lizard brain.

"Fool Moon - The Dresden Files, Book 2" Chapter 15:

"I could have sworn I saw her face start to change, her bared teeth begin to grow into fangs. Maybe that was just the effect of the magic on my perceptions, though, or a primitive, lizard-brain sort of reaction to Tera rising to her feet and charging toward me with a howl. There was murder in her eyes. I hadn’t gotten beaten up twice, shot, and nearly strangled to get taken out by a misguided werewolf bitch."
by lizardgirl October 30, 2012
The act of becoming so high that you act on only natural insticts.
"Mannnn I was tweaking after that first blunt but after the thirteenth I was lizard brain"
by SCarter October 28, 2007
The disconnection one feels from being in a state of lacking (typically physical needs that throw off homeostasis) in times when needed to perform.
Hunger, fatigue, dehydration and other symptoms in the body can lead to feeling like a basking lizard on a rock.
Signs of Lizard Brain include but are not limited to: disconnected speech, idle thinking and stillness, stumbling on words, intense desire to hunt for food or water, prolonged closing of one's eyes yet staying awake, and being drawn to warmth. Signs typically improve after acquiring one's needs and the ability to focus on the task at hand returns.
"Dude, I drank way too much last night and I am really out of it today."
"Go get some water to shake off that lizard brain. You are obviously thirsty and we need to get this project submitted."
*one trip to the water fountain later*
"Alright, thanks. I needed that. What's next?"
by SilentHound216 February 19, 2021
A long-forgotten memory that has been dormant in the back of your mind for years or decades. Different from a regular memory because it's something you haven't thought of since you first experienced it.

Usually more personal, because the more people have the same memory, the more unlikely you are to have forgotten it

Examples:

VHS movies from your childhood (i.e Goodnight Moon VHS 2000, literally any straight-to-VHS Disney movie)
TV shows or commercials (i.e Crashbox on HBO Kids, )
Flash games (i.e Cartoon Network Resort, Interactive Buddy, Habbo Hotel)
Discontinued food/drink brands (i.e Dunkaroos, Blue Pepsi, Green Hulk Hershey's Syrup, Heinz EZ Squirt)
"Dude I just found this old Peter Rabbit VHS that my mom used to put on for me when I was a kid. I haven't thought of this since I was like 6 years old, it's a complete Lizard Brain Memory"
by cormacwalsh September 12, 2021
Relevant to multi tasking, menial or as a distraction.
I don't want to play elden ring. like mostly everything, seems to be a task to allocate to the lizard brain whilst astrally projecting and out genicyding in some form even if terrorising the occupant of a place you're angling to buy or trying to hasten your inheritance from that rich uncle.
by buriedtoodeep April 24, 2022