Temporal lobe · Grey Matter

The temporal lobe is the lower side of each hemisphere, below the lateral (Sylvian) fissure, that turns sounds and shapes into things recognised: it hears, it knows what a word or an object means, it recognises faces, and on its inner face it forms new memories.

Temporal lobe. The temporal lobe is the lower side of each hemisphere, below the lateral (Sylvian) fissure, that turns sounds and shapes into things recognised: it hears, it knows what a word or an object means, it recognises faces, and on its inner face it forms new memories.

Its functions are laid out in bands. On the upper surface, folded into the lateral fissure, sits the primary auditory cortex on Heschl's gyri, with the left Wernicke's area behind it. Along the lateral and lower surface the ventral visual stream recognises objects and faces, ending in regions such as the fusiform gyrus. The anterior tip works as a hub where the features of a concept (its shape, sound, use and name) are bound together. The inner, medial surface holds the hippocampus and the amygdala, the core of memory and emotional learning.

Damage depends on which band is hit. Upper temporal lesions on the left disturb the comprehension of speech, bilateral ones can leave hearing intact and sound recognition lost (auditory agnosia); anterior temporal degeneration erodes the meaning of words and objects (semantic dementia); medial temporal damage prevents new memories, as in the patient H.M.

It is the most common origin of focal seizures in adults, through the hippocampus, which links this card to epilepsy.

Music, voices and the emotional tone of speech engage the right temporal lobe more than the left.

Questions: What happens in the brain when you get a joke and laugh? Getting the joke is detecting an incongruity and resolving it, and imaging links that step to the temporo-occipital-parietal junction and the temporal lobe, with the prefrontal cortex helping to reinterpret the setup. Enjoying it engages the reward network: the amygdala, the ventral striatum with the nucleus accumbens, and the midbrain dopamine regions. Laughter itself is a motor act driven partly from the brainstem and the motor areas, which is why it can be hard to suppress once it starts. What happens when the front of both temporal lobes degenerates? Semantic dementia, a form of frontotemporal degeneration, strikes the anterior temporal lobes first, and the result is a slow loss of meaning across every modality. Patients cannot name objects, then cannot say what they are for, then fail to recognise them from pictures, sounds or touch, with specific knowledge going before general (a dog becomes an animal, then a thing). Recent events and everyday routines are relatively spared, the opposite of hippocampal amnesia, which is the main evidence for a semantic hub in the anterior temporal lobes. What does the right hemisphere add to language if the left does the words? The right temporal and frontal cortex handle much of the melody of speech (prosody): the rise of a question, the emphasis that changes meaning, the tone that signals irony or anger. They also help with what is meant beyond the literal words, such as jokes, metaphors and the thread of a story. After a right-hemisphere stroke a person may speak grammatically in a flat voice, or miss that a remark was sarcastic, a deficit called aprosodia. Where does sound reach the cortex, and how is it laid out there? Sound reaches the cortex on Heschl's gyri, on the upper surface of the temporal lobe hidden inside the lateral fissure, after relays in the brainstem and the medial geniculate nucleus of the thalamus. The primary auditory cortex there is laid out by frequency, low tones at one end and high tones at the other, copying the layout of the cochlea. Each side hears both ears, so damage to one auditory cortex barely affects hearing, while the belt areas around it go on to identify voices, words and melodies.