If you study one neuron, you're a neuroscientist; if you study two neurons, you're a psychologist. Not a side-splitter, that one, but a joke that nicely describes old-fashioned attitudes to brain science: that the only real science is the hard science, and speculation about human meaning should be left to theorists in the psychology department or dreamers in the humanities. Up until about 20 years ago, if a neurologist started tinkering with the problem of consciousness, his colleagues could put it down to the onset of "philosopause".

Since then, the decade of the brain has come and gone, Oliver Sacks has been canonised and no self-respecting neuroscientist can acquire much of a name without publishing a book about the neural correlates of empathy, God, the nonexistent self or the disappearing-coin trick. Reinforced by big authors in cognitive and evolutionary psychology, this has become the busiest market for popular science writing. But amid the frenzied neuronal buzzing, it is often hard to distinguish the brilliant from the banal, or actual neuroscientific developments from roaming speculations.

The most vaunted speculations of the year have come from David Eagleman's Incognito (Canongate £20), which seeks to persuade us that contemporary neuroscience has transformed our understanding of every aspect of individual and social existence, revealing conscious thought to be a mere fragment of our mental processing and the self as an illusion that does not actually exist on any map of neuroanatomy.

He presents this as good news, in the sense that the cosmic circuitry of the brain has been revealed to be even more astonishing than previously imagined. A more cautious reading, however, will reveal that this is neither good nor bad, since it is not news at all. Philosophically, Eagleman moves us no further on from David Hume's "bundle theory" of the self, merely adding aspects of neuro-functioning to a well-trodden philosophical problem. Eagleman relies largely on familiar case histories, written up in a style of conceptual generalisation which left me nostalgic for the clinical observations of Oliver Sacks or Paul Broks.

A more substantial and original neuroscientist, VS Ramachandran, provides the best introduction to the field in The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human (Heinemann £20), a lucid account of what we can actually know about neuroanatomy, turbocharged by enjoyable flights of speculation into what it all may mean.

Ramachandran does best what neuroscience does best, which is to reveal the workings of the mind through the malfunctions of the brain. It's good to be reminded that, though fMRI scans are remarkable, neurologists still learn more about mental functioning by spending time with patients. Particular types of brain damage point to corresponding mental deficits from which the normal functions performed by those regions may be deduced.

Where Ramachandran really wants to fly is in the area he has made his own: the discovery of mirror neurons and the wild speculation that they form the foundation of empathy and, thus, the origin of distinctively human mental abilities arising some 150,000 years ago. But by taking the simple metaphor of "mirror neurons" and transforming it into the more complex one of "empathy neurons", Ramachandran inevitably strays into the philosopause. What is empathy? Is it sufficiently cogent as a conceptual entity to be ascribed distinct neural correlates? Do we empathise with a dying Nazi in the same way as we do with a dying child? The mental calculations required to take the imaginative leap into empathy surely require not just one constellation of neurons, but the wider galaxy of the "social brain".

Which is where Simon Baron-Cohen locates his signature deficit. A world-leading expert on autism, Baron-Cohen has been crucial in distinguishing it as a condition caused by flaws in parts of the brain involved with social interaction. But in Zero Degrees of Empathy (Allen Lane £20), he claims to be "drilling down into the brain-basis of empathy". He seeks a medical-scientific description of evil, defined as an absence of empathy. As an exploration of the brain, the book is characteristically brilliant. As an analysis of the problem of evil, it suffers from acute deficits in the region of moral philosophy.

Scientific explanation without philosophical understanding is no explanation at all. An accessible philosophical account of the problem of the self – its existence or nonexistence – comes in the form of Julian Baggini's The Ego Trick: What Does it Mean to Be You? (Granta £14.99), but a really, enjoyably, angry rebuttal of the "neurotrash" of speculative brain science comes from Raymond Tallis in his Aping Mankind: Neuromania, Darwinitis and the Misrepresentation of Humanity (Acumen £25). It does not detract from the work of serious neuroscience to have some of its contemporary pretensions punctured by one of its own practitioners. Sometimes, Tallis goes too far, disregarding the sharp gleams of fascination in the field, but he is both philosopher and neuroscientist and this is a necessary corrective.

When it comes to putting two neurons together to make a psychological theory, Daniel Kahneman's Thinking, Fast and Slow (Allen Lane £25) is a classic of modern psychological science and the first self-help book written by a Nobel laureate in economics; but there are still some out there who haven't gone down either the cognitive or neuroscientific routes, keeping alive what we must now call "psychodynamic" ideas. It's a relief to discover that someone can still take Freudian psychodynamics seriously, as Darian Leader does in What is Madness? (Hamish Hamilton £20) – though that also means persisting with some silly ideas too. And Lisa Appignanesi writes with beautiful psychological insight in All About Love: Anatomy of an Unruly Emotion (Virago £20) – not, thankfully, about the neural correlates of love, but the phenomenon itself. We don't, after all, hold hands among neurons; instead, we embrace each other in the phenomenal realm, which is our reality, even if it doesn't physiologically exist.