iated with poor numeric manipulation, poor mental arithmetic skill, and the inability to either understand or apply mathematical concepts.
Depression is linked with a hyperactive right hemisphere, with evidence of selective involvement in "processing negative emotions, pessimistic thoughts and unconstructive thinking styles", as well as vigilance, arousal and self-reflection, and a relatively hypoactive left hemisphere, "specifically involved in processing pleasurable experiences" and "relatively more involved in decision-making processes". Additionally, "left hemisphere lesions result in an omissive response bias or error pattern whereas right hemisphere lesions result in a commissive response bias or error pattern." The delusional misidentification syndromes, reduplicative paramnesia and Capgras delusion are also often the result of right hemisphere lesions.
Lateralization of language processes
Hemispheric lateralization refers to the distinction of functions of the right and left hemispheres of the brain. If one hemisphere is more heavily involved in a specific function, it is often referred to as being dominant (Bear et al., 2007). Language and speech understanding and function is commonly accepted by linguists and neuroscientists to be a heavily lateralized function. Many specific aspects of language are found to be localized in the left hemisphere, while less so in the right hemisphere as the left hemisphere is most often dominant. This was proposed first through early work in patients with aphasia and language deficits found to have specific areas with lesions and damage.
When looking at patients that have unilateral hemisphere damage, in either the right or left hemisphere their language deficits can be studied. For example; when the left hemisphere has been damaged or lesioned, the right hemisphere is used to take over some functions via brain plasticity, and this damage of the one hemisphere and compensation by the opposite hemisphere creates language understanding and production changes and deficits that can be studied to examine and determine the basis and interaction of brain areas in language processes.
The production of language and language comprehension require the coordination of different subprocesses in time. Though there is debate on how these subprocesses work together and how thinking and comprehending can change, the anatomical basis and role of a loop involving Wernicke’s and Broca’s area is usually agreed upon.
Neuroscientists generally agree that around the lateral sulcus (or Sylvian Fissure) in the left hemisphere of the brain, there is a neural loop involved both in understanding and producing spoken language. At the front end or beginning of this loop lies Broca's area, which is usually associated with the production of language, or language outputs. At the other end, or specifically in the superior posterior temporal lobe, lies Wernicke's area, which is associated with the processing of words that we hear being spoken, or language inputs. Broca's area and Wernicke's area are connected by a large bundle of nerve fibres called the arcuate fasciculus.
Handedness and language
Broca's area and Wernicke's area are linked by a white matter fiber tract, the arcuate fasciculus. This axonal tract allows the neurons in the two areas to work together in creating vocal language. In more than 95% of right-handed men, and more than 90% of right-handed women, the left hemisphere is dominant in certain aspects of language and speech processing. In left-handed people, the incidence of left-hemisphere language dominance has been reported as 73% and 61%, suggesting left handed people tend to be less lateralized than right-handed people in language function. In general neuroimaging methods, such as functional magnetic resonance imaging and magnetoencephalography, involvement of both hemispheres in many aspects of language processing has been show. The "dominance" discussed in many of these studies simply refers to more brain activation relative to the other hemisphere (or better performance by that hemisphere o