Human language depends on the coordinated activity of a relatively small number of brain areas, located in the left hemisphere for about 95% of humans and in the right hemisphere in the other 5%.

To understand a spoken word, it must first be processed by the auditory cortex. From there, the signal is passed to a nearby area (the posterior part of Brodmann 22, called 22p). This area, named Wernicke’s area after its discoverer, is responsible for breaking down the sounds of speech and extracting meaning from them. Patients with a lesion in this area (Wernicke’s aphasia) not only don’t understand your speech — they don’t understand their own.

Once you’ve made sense of speech, you need to transfer that information to an area that will figure out a plan to move the necessary muscles to make a response. The pathway that carries this information is the arcuate fasciculus. It ends in Broca’s area, discovered by Paul Broca, a 19th century French neurologist. Broca had several patients who could not produce speech. He collected their brains after their death and found each had a lesion in the area that now carries his name.

Broca’s area not only formulates the motor commands for speaking, but also for writing or sign language — basically, any kind of symbolic language. Patients with Broca’s aphasia cannot produce symbolic language. They can’t speak (except for perhaps a few words); they can’t write down what they feel or what they want. This commonly happens after a stroke on the left side of the brain which destroys the brain tissue needed for this critical function.

Complex symbolic language is a human-specific, complex behavior. Another human-specific, complex behavior is our learning and memory system.

There are three stages to making a memory. First it must be encoded, a process that makes sensory information relevant; then it is consolidated, moved from short-term storage to long-term; and if we want it later, it needs to be retrieved.

The storage of memories is in the area of cortex that processes that sensation. For example, visual memories are stored in the visual cortex. The process that stores memories occurs at the level of synapses and is called long-term potentiation. The process of memory storage may be preceded by a series of electrical waves called ripples.

However, there are a group of structures that do the “labeling” and “filing” of memories. Memories are moved from short-term, “scratchpad” memory to a more permanent form. This process is called consolidation.

Declarative memory (explicit memory) is remembering facts, dates and events (where your car keys are; “Columbus sailed the ocean blue in 14 hundred and 92”; your wedding anniversary; where you were when you proposed to your future wife or your future husband proposed to you). These are consolidated in the hippocampus and diencephalon.