Stephen van Vlack
Sookmyung Women`s University
Graduate School of TESOL
Human Learning and Cognition
Spring 2006
Week 14 Answers - Lieberman (2000 Chapter 4
1. What are the functions that basal ganglia circuits carry out? And according to neurophysiologic studies, how are the basal ganglia processing related to language, higher cognition and perception? (Li4)
The basal ganglia are involved in learning particular patterns of motor activity and play a part in sequencing the individual elements that constitute a motor program. Studies show that damage to the stratum disrupts the integrity of the sequence of gestures. Other studies of spatial sequencing in monkeys support that sequencing demands on the activity of many cortical area, caudate nucleus and other basal ganglia structures. Also, they channel sensory information from and to various cortical areas, integrating it with linguistic information. In other words, basal ganglia also sequence cognitive/linguistic operations besides physical movement.
According to neurophysiologic studies, they show that neural circuits link basal ganglia and cerebellum to prefrontal cortical area associated with cognition and cortical areas associated with motor control. Speech, lexical access, the comprehension of meaning and various aspects of higher cognition are regulated. Parallel processing by parallel circuits occurs in neural structures associated with motor control as well as in parts of the brain associated with language, higher cognition and perception. Middleton and Strick (1994) conclude that
The cerebellum and basal ganglia should no longer be considered as purely motor structures. Instead, concepts about their function should be broadened to include involvement in cognitive processes such as working memory, rule-based learning, and planning future behavior.
2. What are the 2 different motor functions of the basal ganglia in human beings? And how do basal ganglia affect cognition? (Li4)
There are 2 different motor functions of the basal ganglia in human beings. First, basal ganglia may promote automatic execution of routine movement by facilitating the desired cortically driven movements and suppressing unwanted muscular activity. Second, they allow and help cortically determined movements to run smoothly. Besides the physical motor function, the basal ganglia are an elaborate machine within the overall frontal lobe distributed system that allows routine thought and action. In other words, we can infer the function of basal ganglia in human
cognition through the function of the frontal lobe that is involved with not only sequencing the movements but also sequencing in cognition such as higher level thought, decision-making, planning and using language. It responds to new circumstances that allow a change in direction of ideas and movement. Thus, loss of basal ganglia contribution such as in Parkinsons disease, would lead to inflexibility of mental and motor response.
3. What are some experiments in nature that explicate the role of basal ganglia and other subcortical structures? (Li4)
There are a variety of experiments that can show the role of basal ganglia and other subcortical structures. Those studies explain that the basal ganglia are essential neuroanatomical components of the functional language system. Some of them are researches on aphasia by Paul Broca. Aphasia is a disorder of language and here two types of aphasia will be explained: Broca`s aphasia and Wernicke`s aphasia.
Broca`s aphasia can be described as expressive aphasia that results from damage to the front portion of the language dominant side of the brain. Broca`s area is located within the left frontal convexity and is responsible for the expression of speech. This area controls speech production and is related to understanding language. There are several characteristics of Broca`s aphasia: nonfluent speech, few words, short sentences, and telegraphic nature. Broca`s aphasia is sometimes called disfluent aphasia or agrammatic aphasia in which speech is labored and slow. Broca`s area is the section of the brain which is involved in speech production, specifically assessing syntax of words while listening, and comprehending structural complexity. People suffering from Broca`s aphasia are unable to understand and make grammatically complex sentences. Speech will consist almost of content words. Sentence length is also short. Average utterance length is typically about 2, and in some cases the patient may only be able to produce single word utterances. Syntax and morphology are affected; only the most basic and over-learned grammatical forms are produced. Broca`s aphasia gives the speech the general appearance of a telegraphic nature because of the deletion of grammatical function words and disturbances in word order. Telegraphic means that articles, conjunctions, prepositions, auxiliary verbs and pronouns and morphological inflections are omitted. In addition, nouns, verbs, adjectives and adverbs (content words) may be retained. Output can be restricted to noun-verb combination. Moreover, the repetition of words and phrases is impaired. Broca`s aphasia involves a lack of ability to produce coherent language, including spoken, written and signed forms.
In Broca`s aphasia, on the other hand, comprehension is actually good and patients who recover go on to say that they knew what they wanted to say but could not express themselves. Patients have no difficulty classifying words along semantic dimensions while they have difficulty comprehending distinctions in meaning conveyed by syntax. Aural comprehension for conversational speech is relatively intact. Patients suffering from Broca`s aphasia are able to use the organs of speech, the articulators, to produce sounds and even single words, but they cannot produce sentences or express thoughts.
Wernicke`s aphasia can be described as receptive aphasia that results from damage to the back portion of the language dominant side of the brain. Wernicke`s area is located within the left superior temporal lobe and extends from the border zones of the primary auditory reception area toward the inferior parietal lobule. This area acts to decode the sounds of language so that spoken as well as written words and sentences can be understood and comprehended. For example, Wernicke`s area provides the auditory equivalent of a visually perceived written word so that we know what the words we read sound like. Some characteristics of Wernicke`s aphasia are comprehension deficits and empty speech. Patients will have great difficulty comprehending spoken or written language. Naming, reading, writing and the ability to repeat or understand what is said are severely effected. They frequently use vague terms and roundabout descriptions but their strings of words often lack coherent meaning. Many receptive aphasics can comprehend frequently used words but have difficulty with those less frequently heard. They will usually have the most difficulty understanding relational or syntactical structures, including the use of verb tense, possessives, and prepositions.
It is also possible to find out the role of subcortical structures in regulating speech from the cases of speech production deficits and cognitive deficits. Patients will often find one word or a short string of words and repeat them over and over in an attempt to communicate thoughts, and may sometimes be successful in communicating, but they will not be able to grammatically express themselves. The key is that they can understand speech, and often can form ideas to communicate, but they cannot put words together to communicate those ideas. Speech production in Broca`s aphasia is not impaired. They have no difficulty controlling the articulators of speech such as tongue, lips, and larynx height.
Cognitive deficits are described as loss of the abstract attitude. Aphasic patients have difficulties whey planning activities and strategies, shifting strategies, formulating abstract categories, and thinking symbolically. Damage either to the prefrontal cortex or to subcortical structures supporting circuits to the prefrontal cortex can yield frontal lobe cognitive deficits. In short, severe language deficits occur in patients who have suffered the most extensive subcortical brain damage.
4. What is the role of subcortical neural structures, especially in language? (Li4)
Only human beings possess language and complex thought, so only data from experiments in nature can explicate the role of basal ganglia and other subcortical structures in regulating these singular human qualities. These human studies show that the basal ganglia are essential neuroanatomical components of the functional language system. In the cortex of Brocas time it was reasonable to equate the language deficits of aphasia with damage to the neocortex. Language clearly is one of the derived features that differentiate human beings from closely related animals such as chimpanzees. Derived features are ones that differentiate a species from other species that have different evolutionary lineages, though they many share a common ancestor. It was reasonable to equate a language deficit, impaired speech production, with neocortical damage. It has become apparent that subcortical neural structures are necessary elements of a functional human language system.
5. How can basal ganglia and deficits such as Parkinson`s disease or hypoxia be related? (Li4)
Parkinson`s disease is a degenerative, progressive neurological disorder that affects nerve cells in the basal ganglia, particularly of that part known as the substantia nigra. Normal neurons talk to each other in the following manner;
1. Incoming messages from the dendrites are passes to the end of the axon, where sacs containing neurotransmitters which are dopamine open into the synapse, a tiny gap between the two nerve cells.
2. The dopamine molecules cross the synapse and fit into special receptors on the receiving cell. So these gates are open when neurotransmitters, dopamine combine the receptors. Therefore, dopamine and the receptors are necessary for passing information.
3. That cell is stimulated to pass the message on.
4. After the message is passed on, the receptors release the dopamine molecules back into the synapse.
For reasons not yet understood, the dopamine-producing nerve cells of the substantia nigra begin to die off in some individuals. Thus, in PD, the basal ganglia cells produce less dopamine, which is needed to transmit vital messages to other parts of the brain, and to the spinal cord, nerves and muscles. Nerve cells in the basal ganglia and the substantia nigra are responsible for planning and controlling automatic movements of the body. When 80% of dopamine is lost, PD symptoms such as tremor, slowness of movement, stiffness, and balance problems occur. A major function of the basal ganglia is regulating sequences of motor acts and cognitive operations. It means PD, which affects basal ganglia function, impairs motor control but also causes deficits in cognition. In fact, Parkinson`s disease shows syntax comprehension deficits. Parkinsons disease also impairs sequential speech motor acts such as production of voice-onset time (VOT). PD patients show reduced differences between VOTs for voiced and unvoiced stops. Such VOT convergence correlates with deficits in sentence comprehension in PD.
The low oxygen content of the thin air can damage the principal basal ganglia output structure, the globus pallidus. That is hypoxia. On Mount Everest, researchers measured cognition by various tests. They failed an implicit contextual learning and at high altitudes, many climbers show VOT convergence and increased vowel duration. It means the basal ganglia was damaged. The climbers made errors in sentence comprehension and other cognitive tests that also may have reflected damage of the basal ganglia sequencing function, responding to new circumstances to allow a change in direction of ideas and movement. Loss of basal ganglia contribution thus would lead to inflexibility of mental and motor response.
6. What causes the sentence-comprehension deficits? (Li4)
7. What are the roles of the cerebellum?(Li4)