Psycholinguistics/Language and the Brain

Overview/Introduction (Language and the Brain)

Language and the brain are intricately related and in order to gain a deeper understanding of Psycholinguistics we must examine this relationship. It is the goal of this page to describe the various brain regions/structures, language processes and the intricate connection between them. The structural anatomy of the brain will be discussed, as it is the fundamental basis of the relationship between language and the brain. In order to understand the nature and dynamics of language we must understand how it relates to the brain. Language is a function of the structure of the human brain and several brain regions have been identified with linguistic capabilities.

Major brain regions (Language Comprehension & Production)

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Broca's Area- Broca's area is one of two key areas involved in language comprehension and production. The area is located in the inferior frontal gyrus and is intricately connected to speech production. This brain area was first discovered by Pierre Broca when he noticed specific speech impairments in the patients he was treating. These patients had lost the ability to speak when damage occurred to this specific region of their brain. This brain region then became known as Broca’s area and the corresponding language production deficit was named Broca’s aphasia. Various studies of patients with chronic aphasia have played an important role in understanding this affliction in relation to speech and language functions. Through the use of diagnostic imaging such as functional MRI (fMRI), Magnetic Resonance Imaging (MRI), many activation areas for a variety of language tasks have been identified within Broca’s area. The discovery of this brain region has shed vast insight into language abilities and functions and is central to the understanding of language, language deficits as well as psycholinguistics capabilities.

Wernicke's Area- Wernicke's area is another very important region of the brain intricately involved with language. As part of the cerebral cortex it is directly linked to speech and involved in the comprehension of written and spoken language(Tyler & Marslen-Wilson, 2008). Wernicke's area is located in the posterior section of the superior temporal gyrus. Specifically, this area encircles the auditory cortex on the Sylvian fissure. It is at the sylvian fissure where the temporal lobe and parietal lobe meet and comprises a portion of Brodmann's area (Casey et al., 2005). Wernicke's area is named after Carl Wernicke (pictured left), who hypothesized there was a connection between the left posterior section of the superior temporal gyrus and the mimicking of words associated with the sensory and motor images of spoken words.

Language localization

The Cerebral Cortex- The cerebral cortex is a composed of a layer of neural tissue at the outer periphery of the cerebrum of the brain and plays a crucial role in a variety of cognitive tasks such as memory, attention, thoughts and language (Fields, 2008). The majority of the cerebral cortex is folded into large grooves called sulci and is made up of sensory, motor and association areas. Six horizontal layers vary in their composition such that neuron or connectivity ratio/composition varies. The cerebral cortex is approximately 2-4mm thick and is composed of gray and white matter (Friederici, 2009). The grey matter is formed from neurons and unmyelinated fibers, whereas the white matter is formed predominantly by myelinated axons. Neurons in different regions of the cerebral cortex communicate with one another as well as with neurons in other parts of the central nervous system, allowing for messages to be sent proximally or distally.

Corpus Callosum- The corpus callosum is a bundle of neural fibers located beneath the cortex in the brain at the longitudinal fissure. It connects the left and right hemispheres and is responsible for directing communication between them. It is important to note that the corpus callosum is the largest white matter structure in the brain, consisting of 200–250 million contralateral axonal projections.

Contralateral Processing- Contralateral processing means that any stimulation of the right motor cortex will induce a body part on the left side move. Conversely, stimulation of the left motor cortex makes the right side move.

Ipsilateral Processing- Ipsilateral processing is the opposite of contralateral processing and is any processing that occurs on the same side of the body. This means that it would be situated on or affecting the same side.

Subcortical structures (Role in language processing)

Limbic System - The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum and limbic cortex, which support a variety of functions including emotion, behaviour, long term memory, and olfaction. This set of brain structures forms the inner border of the cortex. Each cortical hemisphere is a section of gray matter, with an area where nerve fibers connected to the subcortical structures of the basal forebrain. This area is surrounded by cortical and noncortical areas that combine to make up the limbic system. The cortical components generally have fewer layers than the 6-layered neocortex.

Basal Ganglia- The basal ganglia/nuclei are a group of nuclei in the brain that act cohesively to function as a unit, not independently from one another. Located at the base of the forebrain the basal ganglia are strongly connected with the cerebral cortex, thalamus and other brain regions. The basal ganglia are associated with a variety of functions, including voluntary motor control, learning routine behaviours, eye movements, and cognitive functions. Recent theories implicate the basal ganglia as being primarily responsible for decisions relating to appropriate behaviours to execute at a given time. Experimental studies have shown that the basal ganglia exert an inhibitory influence on a number of motor systems and allow motor system activation (Casey et al., 2005). When we switch between different behaviour it is directly related to the basal ganglia but if also influenced from various other brain regions. One of these brain regions directly influencing signals to the basal ganglia is the prefrontal cortex, which plays a key role in executive functions. The basal ganglia play a central role in a number of neurological conditions, including several movement disorders.

Many brain structures play a critical role in brain functions, specially language acquisition, production and comprehension. It is important to understand these structures in order to better understand how the brain and language are intricately related. Through the evolution of diagnostic imaging researchers can gain this better understanding. As technology and human research interests evolve together, a better understanding of how exact brain regions influence the various dynamic aspects of language.

Brain imaging (Methods used to study the brain)

Various techniques and methods are used to identify and study brain structures, functions and abnormalities. It is through these imaging techniques that we can gain a deeper understanding of how the brain works on a neural or cellular level. When images are obtained through brain scanning we can determine specific activation areas of the brain when various functions are carried out such as speech production, listening or thinking. It is through these methods that lead to a better understanding and future areas of research in brain and language related matters. The discoveries of abnormalities in the brain, such as a tumour, show how deeply brain areas can be afflicted and what processes are hindered as a result of the disease. It also allows for further mapping of the human brain.

Brain Imaging Method	Description
CAT Image obtained from: CAT Scan]]	Computed Axial Tomography, (CAT), is a method of brain imaging that was created in the 1970s and is used quite commonly across the world. This imaging method has the unique ability to image tissue, bone, and blood vessels. CAT is based on the x-ray model in that as x-rays pass through the body, they are absorbed at varying levels. X-ray beams are passed through a patient’s brain/skull in order to measure the level of radiation that is permitted passage. An x-ray profile is the resultant product and is transferred to film to create an image available for analysis.
PETImage obtained from: PETScan]]	Positron emission tomography (PET) is a nuclear medicine imaging technique which produces three dimensional images of brain processes. In the 1950s PET was introduced by David Kuhl and Roy Edwards. In order to conduct a scan, a radioactive tracer isotope is injected into a living subject, most generally directly into blood circulation and this tracer becomes chemically incorporated. After a brief waiting intermission to ensure activation occurs, the subject is placed in the imaging scanner. The emitted positron travels in tissue for a short distance, losing kinetic energy, until is capable of interacting with an electron and it is when this decay occurs positrons are emitted. This process eliminates both electron and positron and depends on detection of the paired photons moving in opposite directions. As the radioactive tracer decays a scan records tissue concentration levels.
MRI Image obtained from: MRI]]	Magnetic resonance imaging (MRI) is an imaging technique used in radiology in order to visualize detailed internal structures. MRI utilizes nuclear magnetic resonance (NMR) to image atomic nuclei within the body. MRI provides significant contrast between varying soft body tissues and this is what makes this imaging technique especially useful in analyzing the brain, compared with other medical imaging techniques mentioned previously. As well MRI does not use ionizing radiation unlike CT scans or traditional X-rays.
fMRI Image obtained from: fMRI]]	A type of brain imaging closely related to MRI is the functional MRI or functional Magnetic Resonance Imaging (fMRI), which is a specialized MRI scan. It measures the change in blood flow in relation to neural activity in the brain or spinal cord of humans. fMRI is one of the most recently developed forms of neuroimaging and since the early 1990s, it has been the predominant method used for brain mapping. This brain mapping method has advantages such as low invasiveness, no radiation exposure and is widely available.
ERP Image obtained from: ERP]]	An event-related potential (ERP) measures brain response in relation to a thought pattern or individual perception using an electroencephalography (EEG). This procedure measures any electrical activity of the brain via electrodes attached to the skull and scalp. The EEG can measure several simultaneously occurring brain processes as well as the brain’s response to a single stimulus. In order to examine the brain’s response to a stimulus, the researcher must average as many as 100 or more trials to obtain significant results. This process ensures that random brain activity is averaged out and any relevant ERP’s remain.

Conclusion

The neural networking and structures of the brain in terms of how they relate to language, comprehension and vocalization have always been a focus of researchers. As technology advances and we are better able to utilize neuroimaging techiniques to analyze the brain and its structures, we will further our understanding of how truly magnificent and complex it is. Language in and of itself is a complex thing and when we research this in terms of neural process patterning in the brain it becomes an increasingly more complex area to study. It is clear that many factors are involved in the acquisition and use of language and that various brain structures have key roles in critical functions. Neuroimaging techniques such as fMRI, MRI and PET scans have vastly increased our knoweledge and ability to study the brain in depth and will only continue to expand upon the knowledge of how our sensory world gets coded in the brain.

Learning Exercise

References

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2. Cohen Kadosh K, Johnson MH. (2007) Developing a cortex specialized for face perception. Trends Cogn Sci. 11:367--369.

3. Fields RD. (2008) White matter in learning, cognition and psychiatric disorders. Trends Neurosci. 31:361--370.

4. Friederici AD. (2002) Towards a neural basis of auditory sentence processing. Trends Cogn Sci. 6:78--84.

5. Friederici AD. (2009) Pathways to language: fiber tracts in the human brain. Trends Cogn Sci. 13:175—181

6. Ghazanfar AA. (2008) Language evolution: neural differences that make a difference. Nat Neurosci. 11:382--384.

7. Glasser MF, Rilling JK. (2008) DTI tractography of the human brain’s language pathways. Cereb Cortex. 18:2471--2482.

8. Hashimoto R, Sakai KL. (2002) Specialization in the left prefrontal cortex for sentence comprehension. Neuron. 35:589--597.

9. Petkov CI, Logothetis NK, Obleser J. (2009) Where are the human speech and voice regions and do other animals have anything like them? Neuroscientist. 15:419--429.

10.Saur D, Kreher BW, Schnell S, Ka¨mmerer D, Kellmeyer P, Vry M-S, Umarova R, Musso M, Glauche V, Abel S, et al. (2008) Ventral and dorsal pathways for language. Proc Natl Acad Sci U S A. 105:18035--18040.

11.Tyler LK, Marslen-Wilson W. (2008) Fronto-temporal brain systems supporting spoken language comprehension. Philos Trans R SocLond B Biol Sci. 363:1037--1054.

12.Vigneau M, Beaucousin V, Herve´ PY, Duffau H, Crivello F, Houde´ O, Mazoyer B, Tzourio-Mazoyer N. (2006) Meta-analyzing left hemisphere language areas: phonology, semantics, and sentence processing. Neuroimage. 30:1414--1432.

13. Weiller C, Musso M, Rijntjes M, Saur D. (2009) Please don’t underestimate the ventral pathway in language. Trends Cogn Sci. 13:369--370.

All images used are from Wikicommons or royalty free images obtained from Boaz Yiftach's at http://www.freedigitalphotos.net/images/view_photog.php?photogid=1408.

	fMRI.
	ERP.
	EEG.
	MRI.

	Eye movements
	Voluntary motor control
	Learning routine behaviours
	All of the above

	Broca's Area
	Primary motor cortex
	Wernicke's Area
	Hippocampus