Could ms located in the spine cause symptoms primarily impairing brain function? like lightheadedness (brain fog) and bad short term memory?

Not related to MS: MS in the spine wouldn't cause any issues with brain function. MS taking place in the brain could cause some issues with lightheadedness but not memory issues, it would have to be a very end-stage degenerative MS to cause such symptoms and even then it would likely be a secondary cause, not a primary. Other things such as vertigo, viral infections, stress, sleep etc could be benign causes of this

Although cognitive problems are very frequent in all stages of MS, this would be an unlikely explanation in the absence of typical lesions seen with brain MRI imaging. If lesions are solely focalized within the spinal cord, and not the brain, this might suggest a diagnosis of Neuromyelitis Optica instead. Discuss these issues with an experienced neurologist.