Cognitive Neuroscience - Test Yourself 2.1 (Question & Answer)

 Cognitive Neuroscience

Test yourself 2.1

1. How did early brain researchers describe the brain in terms of a nerve net? How does the idea of individual neurons differ from the idea of a nerve net?

The brain appears to be almost solid when seen with naked eye. However, a stained view of the brain tissues under a microscope shows that billions of smaller units form the brain by contrasting different types of tissues. The electrical signals and the pathways through which they travel in the brain appear like a continuous network called the nerve net that connects directly to another for conducting signals uninterrupted through the network.

Brain has a continuous, interconnected nerve net; but microscopes and early staining techniques could not resolve the small details. Later, Camillo Golgi stained the brain tissues in a solution of silver nitrate by which the cells were stained randomly making this technique more suitable for viewing the 1% stained cells that stood out from the rest of the tissue and possible to see their structure.

Individual neurons differ from the nerve net and this was observed by Ramon y Cajal when he used two different techniques, one of Golgi staining and another from tissue from the brains of the animals that are newborn. He then observed neurons that were individual units that are the basic building blocks of every brain. These cells are not present in continuation with other cells and they transmit signals in the nervous system.

2. Describe the research that led Cajal to propose the neuron doctrine.

All the organs of the body function properly in assistance with the nervous system. Sensory stimulus from receptor neurons are relayed as electrical signals across to the central nervous system. These are processed for sensory perception into the memory by the brain; that leads to a response by the respective part of the body.

Brain is a complex structure which works as an interplay of coordinated interactions between axonal branches, neuromodulators, cell types, dendritic spines, and neurotransmitters. The brain organizes and localizes specific information and functions in specific areas of the brain, like the cerebral cortex serves the cognitive functions and frontal lobes receives electrical signals and coordinates the information that is received via two or more than two senses. However, different areas of brain often come together to cause an effect.

The brain appears to be almost solid when seen with the naked eye. However, a stained view of the brain tissues under a microscope shows that billions of smaller units form the brain by contrasting different types of tissues.

Ramon y Cajal used two different techniques. One was of Golgi staining where he stained the brain tissues in a solution of silver nitrate; by which the cells were stained randomly making this technique more suitable for viewing the 1% stained cells which stood out from the rest of the tissue and possible to see their structure. He also stained another from tissue from the brains of the animals that are newborn. He then observed neurons that were individual units that are the basic building blocks of every brain. These cells are not present in continuation with other cells and they transmit signals in the nervous system.

3. Describe the structure of a neuron. Describe the synapse and neural circuits.

Brain is a complex structure which works as an interplay of coordinated interactions between axonal branches, neuromodulators, cell types, dendritic spines, and neurotransmitters. The brain organizes and localizes specific information and functions in specific areas of the brain, like the cerebral cortex serves the cognitive functions and frontal lobes receives electrical signals and coordinates the information that is received via two or more than two senses. However, different areas of brain often come together to cause an effect.

The brain appears to be almost solid when seen with naked eye. However, a stained view of the brain tissues under a microscope shows that billions of smaller units form the brain by contrasting different types of tissues.

Ramon y Cajal used two different techniques. One was of Golgi staining where he stained the brain tissues in a solution of silver nitrate; by which the cells were stained randomly making this technique more suitable for viewing the 1% stained cells which stood out from the rest of the tissue and possible to see their structure. He also stained another from tissue from the brains of the animals that are newborn. He then observed neurons that were individual units that are the basic building blocks of every brain. These cells are not present in continuation with other cells and they transmit signals in the nervous system.

Information is picked from the environment (via the skin, eyes, ears, and others). They have a cell body, axon and specialized receptors that pick information from the environment. All the neurons have a small gap known as the synapse. The neurons do not connect indiscriminately to other neurons, but are connected to specific neurons forming neural circuits.

4. How are action potentials recorded from a neuron? What do these signals look like, and what is the relation between action potentials and stimulus intensity?

Action potential is a short-lasting event that occurs when an electric signal is passed down to axon. It occurs in several cells of animals, including neurons and muscle cells, and also in some plant cells.

Action potential occurring in the neurons is also called as nerve impulse. This nerve impulse rapidly rises and falls, when an electric signal is transmitted. It plays a vital role is communication between cells in neurons and helps in the functioning of brain.

The action potentials are recorded from the neurons using two electrodes. Electrodes can be either of glass or metal. One end of an electrode, called recording electrode, is positioned near a neuron, and other end is connected to other electrode called reference electrode.

Thus, the action potential will be recorded from the difference between the recorded and reference electrodes. This difference is shown in an oscilloscope and is shown by a vertical position of a small dot. The difference will be  without the transmission of electric signal in the neuron.

When the signal is transmitted, the dot moves up and then comes back to its original position. If it is compressed in the time scale, the action potential appears as a vertical line. The series of these vertical lines will indicate the number of action potentials travelling down the axon.

When the signal is transmitted or the body experiences any stimuli, the action potential causes a brief positive pulse and comes back to the original position. Thus, action potentials look like small repetitive spike-like events.

Figure: Graph showing relationship between action potential and time.

Some of the features of action potential are as follows:

1. It has a short duration.

2. It is elicited only in response to the stimuli.

3. Its frequency is directly proportional to the intensity of the stimuli.

Relation between action potential and stimuli intensity:

When the intensity of stimulus is increased, the size of the action potential does not increase. The height and shape of the action potential remains same, but number of action potential increases. Thus, greater the intensity of the stimulus greater will be the number of action potentials elicited.

The stimulus can be of light, sound, smell, touch and others. The number of action potentials travelling down the axon every second is called as the rate of nerve firing. Relation between some of the stimuli and the rate of nerve firing are given as follows:

1. If the intensity of the light stimuli is high or when a brighter light is presented before the eye, the rate of nerve firing increases in the visual system.

2. Similarly, if the skin experiences high pressure over it, the rate of nerve firing increases rapidly in the touch system present in the brain.

5. How has the question of how action potentials indicate different qualities been answered?

Action potential is a short-lasting event occurred when an electric signal is passed down to axon. It occurs in several cells of animals including neurons and muscle cells, and also in some plant cells.
Action potential occurring in the neurons is also called as nerve impulse. This nerve impulse rapidly rises and falls when an electric signal is transmitted. It plays a vital role is communication between cells in neurons and helps in the functioning of brain.

When the body experiences stimuli, which can be a light, sound, smell or touch, the action potential causes a brief positive pulse and comes back to the original position. Thus, action potentials look like small repetitive spike-like events.

Some of the features of action potential are as follows:

1. It has a short duration.

2. It is elicited only in response to the stimuli.

3. Its size remains the same regardless of the intensity of stimulus.

4. Its frequency is directly proportional to the intensity of the stimuli.

The action potential or nerve impulses are transmitted to the different areas of brain depending on the cognitive function, and this principle is called as localization of function. Thus, the different qualities of the action potential are defined by this principle. Action potentials help in various functions, such as hearing, vision, smell, taste and many other cognitive functions. Most cognitive functions are carried out by cerebral cortex.

Thus, the nerve impulses are transmitted to different areas of cerebral cortex depending on the stimuli, and are given as follows:

1. When the bright light stimulates the receptors in the eye, the action potentials are transmitted to the visual area located in the occipital lobe.

2. When the light stimulates the receptors near the ear, the action potentials are transmitted to the auditory area located in the temporal lobe.

3. When the smell stimulates the receptors near the nose, the action potentials are transmitted to the underside of the temporal lobe.

4. When taste stimulates the receptors in the tongue, the action potentials are transmitted to the small area within the frontal lobe.

5. When the skin experiences pain, temperature or touch over the skin, the action potentials are transmitted to the parietal lobe.

6. Describe evidence for localization of function for perception, including the primary receiving areas of the brain and evidence from brain damage and brain imaging. Be sure you understand the principle behind brain imaging.

When the body experiences stimuli, which can be a light, sound, smell or touch, it causes a brief positive pulse along the neuron. Action potential plays a vital role in communication between cells in neurons and helps in the functioning of brain.

Action potential occurring in the neurons is also called as nerve impulse. They are transmitted to the different areas of brain depending on the cognitive function, and this principle is called as localization of function. Most cognitive functions are carried out by cerebral cortex.

Primary receiving areas of brain are as follows:

1. When the bright light stimulates the receptors in the eye, the action potentials are transmitted to the visual area located in the occipital lobe.

2. When the light stimulates the receptors near the ear, the action potentials are transmitted to the auditory area located in the temporal lobe.

3. When the smell stimulates the receptors near the nose, the action potentials are transmitted to the underside of the temporal lobe.

4. When taste stimulates the receptors in the tongue, the action potentials are transmitted to the small area within the frontal lobe.

5. When the skin experiences pain, temperature or touch over the skin, the action potentials are transmitted to the parietal lobe.

The above mentioned primary areas of brain were identified by the effects of brain damaging. Depending on the part of brain damaged, the following perceptual effects were found in the patients:

1. Damage in the occipital lobe causes blindness.

2. Damage in the auditory area of the temporal lobe causes deafness.

3. Damage in the lower right side of the temporal lobe causes a condition called prosopagnosia, that is, difficulty in recognizing the faces.

4. Mild and moderate brain injury causes headache, memory problems, confusion and nausea.

5. Severe brain damages like damage in many areas of brain or neurological illness causes stroke.

To demonstrate the localization of various functions of the cerebral cortex, a technique called brain imaging has been used. This technique shows that creation of images activates which areas of the brain. Two brain imaging techniques are given as follows:

1. PET (Positron Emission Tomography) - Using this technique, blood flow in the brain is measured. It shows that the blood flow increases in those areas that are activated by any cognitive task. A low dose is injected in the blood stream of a person. When a high signal is noticed, it indicates the higher level of brain activity.

2. fMRI (Functional Magnetic Resonance Imaging) - This technique is also used to measure the blood flow in brain. Due to the presence of ferrous molecule in hemoglobin, a magnetic field is presented to the brain. This field will cause the molecules to lineup in the areas of high brain activity. Thus, the brain activity is detected from the magnetic response of the hemoglobin.

7. How did Broca and Wernicke use the behavior of patients with brain damage to provide evidence for localization of function?

The principle of localization of functions says that whenever the body experiences any stimuli, the nerve impulse or action potential causes a positive pulse along the neuron. Different stimuli allow the brain to perform most of the cognitive functions.

The evidence of this principle is also given by some of the neurologists named Paul Broca and Carl Wernicke. They studied the patients with brain damages and provided the evidence that those patients had difficulty in speaking or understanding the language.

According to the study of Broca, damage in the frontal lobe of the brain caused difficulty in patients for producing the language. These patients do not had any difficulty in understanding the language, but only in speaking. Thus, the area in the frontal lobe is named as Broca’s area, and the condition with this difficulty is called as Broca’s aphasia.

Later, by other researchers, the difficulty in these areas was named as forms, as patients have difficulty in forming a sentence with correct grammar or jumbled sentence structure. The researches provided the fact that Broca’s aphasia is not only the problem of producing language, but also in relating different words in a sentence.

According to the study of Wernicke, damage in the temporal lobe of the brain caused difficulty in the patients for producing meaningful speech, writing and in understanding the language.

Thus, the area in the temporal lobe is named as Wernicke’s area, and the condition with this difficulty is called as Wernicke’s aphasia. Later, the Wernicke’s aphasia is named as form and meaning which means the patients could not speak and understand the meaning of the sentences.

8. What behavioral evidence caused a modification of the idea of two areas, one for language production and one for language understanding? What is the ERP, and how has it been used to demonstrate different aspects of language functioning? What basic conclusions about localization of function have emerged from research on the physiology of language?

Paul Broca and Carl Wernicke were the two neurologists, who provided the evidence of localization of functions principle. They studied the patients with brain damages and provided the evidence that those patients had difficulty in speaking or understanding the language. The results of both these studies are given as follows:

1. Broca’s Study- Damage in the frontal lobe of the brain caused difficulty in patients for producing the language.

2. Wernicke’s Study- Damage in the temporal lobe of the brain caused difficulty in the patients for producing meaningful speech, writing and in understanding the language.

After the proposal of these two studies, their models were accepted for many years. Later, many other researchers have demonstrated behavioral and physiological experiments to distinguish the problems of form and meaning. This can be given as follows:

1. Form means patient will have difficulty in relating the words in a particular sentence, like in Broca’s study.

2. Meaning indicates those patients, who could not understand the meaning of the sentence, like in Wernicke’s study.

The modification occurred in 1970’s, when researchers demonstrated behavioral experiments in both Broca’s and Wernicke’s aphasia. The researches provided the fact that Broca’s aphasia is not only the problem of producing language, but also in relating different words in a sentence.

Broca’s patients can understand the language, but could not form the sentence. Also, the patients who could not speak, write and understand have the problem of both form and meaning as in Wernicke’s aphasia. Thus, they modified the problem of production and understanding into form and meaning in language.

One of the methods used to distinguish form and meaning is Event-related Potential (ERP), where the number of waves is measured by presenting different stimuli before a person. Positive and negative responses in the waves differentiate the efficient functioning of brain and brain with disabilities due to damages. These positive and negative components are represented by N400 and P600. The demonstration is given as follows:

 If a person hears an incorrect sentence, which alters the meaning, the person’s N400 response becomes larger. Thus, in a sentence, he is sensitive to meaning of words.

If a person hears a sentence with improper grammar, the person’s P600 component becomes larger. Thus, he is sensitive to form of a sentence.

After the demonstration of form and meaning differences in language, hundreds of experiments have been proposed to show physiology of the processing of language. These experiments were more complex, compared to Wernicke’s and Broca’s aphasia. The following conclusions were made on localization of functions from all these researches:

1. Localization of functions plays a vital role in language processing and specific functions are performed in specific areas of brain.

2. These specific areas in the brain do not constitute a small area, but a large area of brain.