Controlling Intentional, Precise LED Flickering for Alzheimer's Treatment

Hey All,
First off, thanks for taking a minute to read a post from a complete newb to Arduino. However, this product seems perfectly suited to help with a project I’d like to take on. See the news article below, I’m not part of the team or employed in the scientific field but I’d like to create a setup that flickers a set of LEDs as close to 40 hertz as possible. I’m in the US, if that’s necessary to know for input current. I have looked through instructions on how to create flicker, but none seem to be able to tune to a specific modulation of 40 times per second. Thanks in advance, I genuinely appreciate any help you can offer.

First heard here, on podcast (very interesting listen):

Welcome to the forum.

Flashing an LED is one of the first things a newbie to the Arduino world learns.
The "Blink" example in the IDE shows you how to flash the onboard LED.
The on/off times are set to 1 second (1000 milliseconds), but you can change that to whatever time you want.
40Hz is a total on+off time of 1000/40 = 25milliseconds.
Just make sure the "on" and "off" times add up to that, and you get 40Hz.
Once you know how it works, you can think of using a more powerful external LED.