What determines whether an atom becomes a positive ion or a negative ion?

 Whether the atom has extra electrons or missing electrons

The group that the element is in in the Periodic Table.
Atoms of elements from groups I to III become positive ions.
Atoms of elements from groups V to VII become negative ions.

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later