Neuron: The basic unit of the brain● Signaling unit● Takes information in, makes a decision about it, and passes it along to other neurons● There are perhaps about one hundred billion neurons in the brain, and in a single humanbrain the number of possible interconnections between these cess is greater than the number of atoms in the universe The Cerebral Cortex● Two symmetrical hemispheres that consist of large sheets of layered neurons● The Right and Left Hemispheres are separated by a fissure, but are interconnected by corpus callosumLateralization of Language● Left-hemisphere dominance for language and speech● Left lateralization of speech may be due to the need to communicate at rapid rates (without taking time for transcortical processing and integration)● In not strongly correlated with handedness○ I.e., 50% of all left-handers are left-hemisphere ● Split-brain experimentsWhat happens if the brain is split?● Corpus callosum is severed in patients with epilepsy● Visual information Aphasia● Language deficits in comprehension and production of language due to neurological damage● Approximately 40% of all strokes produce aphasia (at least in the acute period)Broca’s Area● Paul Broca● Autopsied a patient with aphasia (who was not able to produce anything but the word “tan”)● Observed that the patient had a brain lesion in the posterior portion of the left inferior frontal gyrus● Studid other aphasic patients, all of whom had left-hemisphere damage, right hemiparesis (weakness), and a language disorder● Broca concluded that the brain areas that produce speech are located in the inferior frontal lobe of the left hemisphere● Now, this region is referred to as Broca’s Area, and a linguistic deficit resulting from damage to it is called Broca’s Aphasia● This area is activated in normal adults during speech production, and also during processing of syntaxWernicke’s Area● Carl Wernicke● Described two patients who had difficulty understanding spoken language after a stroke● Unlike Broca’s patients, these patients had fluent speech, but spoke nonsense words and sentences (jargon)● Listening to someone with Wernicke’s aphasia is akin to listening to someone speaking aforeign language● Post-autopsy, Wernicke discovered damage in the posterior regions of the superior temporal region● Assumed that that’s where spoken forms of words are stored ● Later, this area became known as Wernicke’s area, and a linguistic deficit resulting from damage to it is called Wernicke’s Aphasia● This area is activated in normal adults when they have to tell two words apartNeural Plasticity● Early in gestation, the system is incredibly flexible and plastic● Neural cells change their form, location, and interconnections● However, non-plasticity is also there: once the cells migrate, they are fated to express the characteristics of that specific brain region● Plasticity is limited postnatally, and no new neurons are generated after development is complete● But...functional plasticity is there!● Denervated cortical regions get re-enervated by adjacent regions● Cortical regions increase in size in response Phantom Limb Experiment● Sensation in a limb that they no longer have● Why is this happening?Early brain damage and the development of language● Children with early brain-damage are delayed in acquisition of linguistic milestones (first word, first sentence, etc.)● However, not as severe as would be expected in adults● And...the site of lesion does not map directly onto the deficit, as it would in adults● Early deficits tend to resolve by school age, and children usually end up somewhere on the lower end of the normal