Ipsilateral

In neuroanatomical terminology, "ipsilateral" refers to something that is on the same side of the body. The prefix "ipsi-" comes from Latin, meaning "same". When used in neuroscience, it's referring to a structure or point of reference that's on the same side of the body or brain as another referenced structure or point.

Contrastingly, "contralateral" refers to something that is on the opposite side of the body. The prefix "contra-" comes from Latin, meaning "against" or "opposite". In neuroscience, this term describes a structure or point of reference that's on the opposite side of the body or brain relative to another referenced structure or point.

For example, if there is a lesion on the left hemisphere of your brain that affects movement, the contralateral impact would be observed in the right side of your body, because motor functions are largely controlled by the opposite side of the brain. However, any effect that this lesion might have on the left side of your body would be considered ipsilateral, because the lesion and the effects are on the same side.

The cerebellum is a bit of an exception to this rule, as its functional connections are primarily ipsilateral. That is to say, the right hemisphere of the cerebellum receives sensory input from and sends motor commands to the right side of the body, and the left hemisphere of the cerebellum connects with the left side of the body. So, if there is a lesion or damage in the right side of the cerebellum, you would expect to see motor deficits (like ataxia or loss of coordination) primarily on the right (ipsilateral) side of the body. This is in contrast to most of the rest of the brain, where inputs and outputs are primarily contralateral.