Hilary Bok pinpoints them:
Determinism does not relieve us of the need to make decisions. And when we make decisions, we need some conception of the alternatives available to us. If we define an alternative as an action that is physically possible, then determinism implies that we never have more than one alternative. But since we cannot know in advance what we will choose, if we define "alternative" this way, we will never know what our alternatives are. For the purposes of deciding what to do, we need to define our alternatives more broadly: as those actions that we would perform if we chose them…Whether this view provides an adequate account of free will is not a problem neuroscience can solve.
Neuroscience can explain what happens in our brains: how we perceive and think, how we weigh conflicting considerations and make choices, and so forth. But the question of whether freedom and moral responsibility are compatible with free will is not a scientific one, and we should not expect scientists to answer it.