The Effect of Physiological Arousal on. Interhemispheric Transmission Time. Cathy Gouchie. Algoma University

Transcription

1 1 The Effect of Physiological Arousal on Interhemispheric Transmission Time Cathy Gouchie Algoma University Running Head: INTERHEMISPHERIC TRANSMISSION TIME

2 2 The Effect of Physiological Arousal on Interhemispheric Transmission Time The rate at which information can be transmitted between cerebral hemispheres may change, depending on the circumstances. An increase in physiological arousal may increase interhemispheric transmission time (IHTT), the time taken for information to cross from one hemisphere to the other. A brief review of relevant neuroscientific facts and some previous IHTT research will provide a better understanding of this hypothesis. Cerebral Hemispheres The cerebrum of the human brain is divided into two physically similar cerebral hemispheres. The functions of the hemispheres are not symmetrical as their appearance might indicate. In right handed people, most language functions are concentrated in the left hemisphere (including Broca's and Wernicke's areas), though emotional inflection is provided by the right hemisphere. The right hemisphere is superior in recognizing faces, and in visual-spatial and melodic skills. According to Segalowitz (1983)

3 3 the right hemisphere seems to be necessary for integrating information and making inferences from that synthesis. In general, the left side of the body is controlled by the motor cortex in the right half of the brain and vice versa. Although uncrossed motor pathways are known to exist, movement of the individual limbs, especially their distal parts, are the concern of the crossed pathways (Keypers, cited in DiStefano, Morelli, Marzi, and Berlucchi, 1980). Also some sensory information from one side of the body is carried to the opposite hemisphere. Visual reception is also crossed in the brain. The optic fibers are partially crossed at the optic chiasm. Because of this, all information projected from the left visual field (to the left of a point where both eyes are focused), is transmitted to the right hemisphere. Information from the right visual field is transmitted to the left hemisphere. If the two sides of the brain were not able to communicate, each would receive different visual images and different sets of information from the

4 4 environment. This is not the case since the hemispheres are joined together by several bundles of connecting fibers, the largest of which is the corpus callosum. Normally, all information received by one hemisphere is shared with the other hemisphere via the corpus callosum. In this way, visual information is integrated and only one image is seen. Neural Transmission The electrical nature of neural transmission involves ions. At rest, the inside of a neuron maintains a negative charge, due to an excess of negative ions, with respect to the outside which contains more positive ions. This resting potential must be altered for a message to be transmitted. If the change in potential is large enough, it passes a threshold and an action potential is triggered. This causes a sudden change in the permeability of the cell membrane, allowing an influx of positive ions. This change, the nerve impulse, spreads down the length of the nerve fiber until it reaches a synapse. The electrical charge in the fiber then returns to normal.

5 5 Each presynaptic terminal measures, in some way, the number of signals arriving as electrical impulses. When a sufficient number has arrived, the terminal releases a neurotransmitter into the synapse. This chemical crosses the synapse to specialized receptors on the postsynaptic membrane of the next neuron. Each receptor is specialized in that it accepts only one of the many neurotransmitters (Thompson, 1985). Some neurotransmitters are excitatory and increase the likelihood that a nerve impulse will be created, while others are inhibitory and reduce the chances of impulse firing. The rate at which a nerve fires depends on the number and type of signals it receives. The firing rate will increase if the neuron receives many excitatory signals together; if it receives many inhibitory signals, the firing rate tends to decrease (Bootzin, Bower, Zajonc and Hall, 1986). The more rapidly a neuron fires, the more neurotransmitters are released, therefore the greater the effect on the receiving neuron.

6 6 Through special techniques, locations of specific neurotransmitter receptors in the brain have been identified. For example, in a study of the monkey brain by Snyder (1975, cited in Bignami and Michalek, 1978), the highest density of acetylcholine (ACh) receptors was found in the putamen, a part of the basal ganglia. The lowest density was in the optic chiasm, with fairly high levels present in various areas of the cerebral cortex, thalamus and hypothalamus, and a lower density in the corpus callosum. However, as noted by Siggins and Bloom (1981), most circuits of the cerebral cortex and their neurotransmitters remain to be determined. Alteration of neurotransmitter activity due to stress Barry and Buckley (cited in Anisman, 1978) described stress as stimulation that requires behavioural and/or physiological adjustments. The stimulation usually, but not always, represents a threat to the animal's well-being. One effect of stress is the arousal of the sympathetic nervous system, leading to physiological change such as increased heart rate, deeper and more rapid

7 7 breathing, and a decrease in the galvanic skin response. These changes mobilize the body for action so the stressor can be better managed. This is inferred by the Yerkes-Dodson Law, which says that higher levels of arousal tend to improve performance for tasks that are simple, or which require little cognitive involvement. The more difficult the task, the more it may be disrupted by high levels of arousal. Another consistent physiological change present during stress is alteration in neurotransmitter activity, including norepinephrine, dopamine, acetylcholine and serotonin (Anisman, 1978). Several factors, listed by Anisman, determine the extent of these changes. Included are the severity of the stressor, predictability of stress onset, and control over stress onset or termination. Most stressors examined in the studies reviewed by Anisman led to changes in neuronal activity. The information reviewed so far in this paper suggests the following line of reasoning. A stressor produces physiological arousal, including alterations

8 8 in neurotransmitter activity, designed to manage the stressor and increase survival of the organism. In man and many other animals, motor control and reception of sensory information for one side of the body is primarily the concern of the opposite, or contralateral, hemisphere of the cortex. Also, many brain functions are lateralized to one hemisphere. An decrease in IHTT, possibly due to changes in neurotransmitter activity or rate of nerve firing, would allow faster integration of vital information. This would offer a distinct advantage to an organism's survival under stressful situations. Producing Physiological Arousal As previously mentioned, physiological arousal produces changes in neurotransmitter activity. Physiological arousal can be induced in experimental subjects by submitting them to loud (approximately 90 db) white noise. The noise should be presented continuously since, if bursts of intermittent noise are not generated by the person himself, it may distract him from what he is doing (Poulton, 1979). Poulton stated that continuous noise can have

9 9 different effects, depending on the nature of the task. The increase in arousal, which accompanies continuous noise, leads to improvement on simple speed or vigilance tasks that respond well to arousal. He pointed out that, while continuous noise by itself does not appear to increase physiological arousal for prolonged periods, having to perform a challenging task in continuous noise may increase arousal more than performing the task in quiet. Measurement of IHTT Most behavioural measures of interhemispheric transmission time are based on reasoning originally proposed by Poffenberger (1912, cited in Bashore, 1981). Simple reaction times (SRT) are measured in response to a stimulus presented to one visual field at a time. A stimulus presented to the right visual field (RVF) is transmitted to the left hemisphere. If a right-hand response (ipsilateral response) is requested, the reaction time should be faster than if the stimulus was presented to the left visual field (LVF) and carried to the right hemisphere. In this case, the information would have to be first

10 10 transferred to the left hemisphere before a righthand response (contralateral response) could occur. The difference in reaction times is assumed to be the time required for the information to cross to the other hemisphere (interhemispheric transmission time). Several factors have been proposed to account for the difference in reaction times between ipsilateral and contralateral responses. As a result of his study, Wallace (1971) stated that the response times were dependent on spatial compatibility of the stimulus and response hand. He requested subjects to cross their hands (crossed position) in half the trials and found that reaction times were fastest when the stimulus and response hand were on the same side, regardless of whether the response was ipsilateral or contralateral. He used a choicereaction time procedure, however, where one stimulus requested a right-hand response, and a different stimulus requested a left-hand response. This is a different, more complex task than that of the simple reaction time experiments. According to Bashore

11 11 (1981), it is reasonable to assume a correspondence amoung task complexity, cerebral activation and the amount of information that must be conveyed between the two hemispheres. Berlucchi, Crea, DiStephano and Tassinari (1977) conducted a similar study but used a simple reaction time paradigm. In addition to the normal presentation of the stimulus, a stimulus was presented at three different visual angles for each subject. The results showed that the advantage of ipsilateral responses over contralateral responses was consistent. This was true whether the hands were in the correct anatomical position or in the crossed position. They concluded that the time of difference between ipsilateral and contralateral responses is best attributed to a difference in the anatomy of the neural pathways involved in the two kinds of responses. Ipsilateral responses are integrated within one cerebral hemisphere and contralateral responses require interhemispheric cooperation. Berlucchi and his fellow workers (1977) also found that ipsilateral responses were faster than

12 12 contralateral responses in both visual fields and for all stimulus positions. This is in agreement with the results of Berlucchi, Heron, Hyman, Rizzolatti and Umilta (1971), where the delay between ipsilateral and contralateral responses remained constant regardless of the degree of eccentricity of the visual stimuli. Bashore (1981), after reviewing these many other studies of IHTT, feels that sufficient research has been done using SRT procedures to demonstrate reliable estimates of IHTT. The average estimate of IHTT using the SRT paradigm is approximately 3.0 msec. Summary If physiological arousal does cause a decrease in IHTT, this change might be measured using a SRT experiment. A noise of 90 db, presented to some subjects during the experiment, should induce sufficient physiological arousal to allow any IHTT differences to be measured.

13 13 References Anisman, H. (1978). Neurochemical changes elicited by stress. In H. Anisman and G. Bignami (Eds.). Psychopharmacology of aversively motivated behaviour (pp ). New York: Plenum Press. Bashore, T. (1981). Vocal and manual reaction time estimates of interhemispheric transmission time. Psychological Bulletin, 89, Berlucchi, G., Crea, F., DiStefano, M. and Tassinari, G. (1977). Influence of spatial stimulus response compatibility on reaction time of ipsilateral and contralateral hand to lateralized light stimuli. Journal of Experimental Psychology, 3, Berlucchi, G., Heron, W., Hyman, R., Rizzolatti, and Umilta, C. (1971). Simple reaction times of ipsilateral and contralateral hand to lateralized visual stimuli. Brain, 94,

14 14 Bignami, G. and Michalek, H. (1978). Cholinergic mechanisms and aversively motivated behaviours. In H. Anisman and G. Bignami (Eds.). Psychopharmacoloqy of aversively motivated behaviour (pp ). New York: Plenum Press. Bootzin, R., Bower, G., Zajonc, R. and Hall, E. (1986). Psychology today: An introduction. New York: Random House. DiStefano, M., Morelli, M., Marzi, C.A. and Berlucchi, G. (1980). Hemispheric control of unilateral and bilateral movements of proximal and distal parts of the arm as inferred from simple reaction time to lateralized light stimuli in man. Experimental Brain Research, 38, Poulton,C. (1979). Composite model for human perfo Rance in continuous noise. Psychological Review, 86, Thompson, R.F. (1985). The brain. New York: W.H. Freeman. Segalowitz, S.J. (1983). Two sides of the brain. New Jersey: Prentice-Hall.

15 15 Siggins, G. and Bloom, F. (1981). Modulation of unit activity by chemically coded neurons. In 0. Pompeiano and C. Marsan (Eds.). Brain mechanisms and perceptual awareness. (pp ). New York: Raven Press. Wallace, R.J. (1971). S-R compatibility and the idea of a response code. Journal of Experimental Psychology, 88,

16 The Effect of Physiological Arousal on Interhemispheric Transmission Time Cathy Gouchie Algoma University

17 IH1 1 Running Head: INTERHEMISPHERIC TRANSMISSION TIME Abstract The effect of physiological arousal on interhemispheric transmission time (IH1 1') was investigated. Since physiological arousal produces changes in neurotransmitter activity, these changes could result in a decrease in IH1 1. IHTT was measured with a simple reaction time (SRT) experiment using an IBM PC model 80 computer and customized software. Physiological arousal was produced in 24 subjects through the presentation of a loud (90 db) white noise. Twelve were not submitted to the noise. The results were inconclusive due to inaccurate measurements of IHI'l. A possible reason for these results could be the location of the stimulus. The light flash presented to subjects to stimulate a response may have been situated too close to the centre of the subject's field of vision rather than in the left or right visual fields.

18 IH 1 1 The Effect of Physiological Arousal on Interhemispheric Transmission Time Though the left and right cerebral hemispheres appear physically similar, there are considerable and well-documented differences in their functions (Segalowitz, 1983). Tactile and visual information is transmitted directly to the hemisphere opposite to the side of the body that received the information. Motor control of the limbs also rests within the hemisphere on the opposite side of the body. The hemispheres are joined together by several bundles of connecting fibers, the largest of which is the corpus callosum Any advantage gained by one hemisphere through lateralization of function, or any sensory information coming into only one hemisphere, is shared with the other hemisphere by transmitting information across the corpus callosum The rate at which information can be transmitted between cerebral hemispheres may change, depending on the circumstances. An increase in physiological arousal may decrease the interhemispheric transmission time (IH I 1'), the time taken for information to cross from one

19 IH I I hemisphere to the other. Vital information could therefore be integrated more quickly, offering a distinct advantage to an organism's survival under stressful situations. IH I I can be measured using a simple reaction time (SRT) experiment. This paradigm is based on reasoning originally proposed by Poffenberger (1912, cited in Bashore, 1981). Simple reaction times are measured in response to a stimulus presented to only one visual field at a time. A stimulus presented to the right visual field (RVF) is transmitted to the left hemisphere. If a right hand response (ipsilateral response) is requested, the reaction time should be faster than if the stimulus were presented to the left visual field (LVF) and carried to the right hemisphere. In this case, the information would have to be first transferred to the left hemisphere before a right hand response could occur (contralateral response). The difference in reaction times is assumed to be the time required for the information to cross to the other hemisphere (interhemispheric transmission time-ihtt). Several behavioral studies have been performed on measurements of IHTT. After reviewing many of these studies of IHTT, Bashore (1981) felt that sufficient research had been done using SRT procedures to

20 IHI I demonstrate reliable estimates of IH'I 1. The average estimate is appc,..,.(imately 3.0 insec. Based on previous am research, it should be possible to compare differences in IHTT under different conditions using the SRT paradigm. If physiological arousal can be induced in some subjects, a decrease in IHTT compared to subjects under normal conditions may be detected. Method Subjects Thirty-six psychology students (eight male, twenty-eight female) at Algoma University took part in this study on a voluntary basis. They were all right-handed, with normal or corrected vision as tested on the Lomb Orthorater. They ranged in age from 18 to 45 years.,,: Jed for their participation with bonus marks in one of their psychology courses. All were treated in accordance with the "Ethical Principles of Psychologists" (American Psychological Association, 1981). Procedure was seated with the head positioned so a fixed viewing distance of 17 cm from the computer screen was maintained. This ensured that the stimulus was presented at the proper visual angle. The

21 IH11 ghl tad rested of the table with the index finger prepared to hold down the response button. Subjects were instructed to focus on the fixation point at all times, and to lift their finger from the button as quickly as possible whenever a stimulus appeared, whether it was to the left or right of the fixation point. Stimuli were presented on the display screen of an IBM PC Model 30 computer utilizing customized software. A small fixation spot remained present in the centre of the screen throughout the session. Before each trial, the computer displayed written instructions to press the button and hold it down when ready to proceed with the trial. Once the button was pressed, and after a delay varying randomly between 500 and 1500 cosec (to discourage anticipatory responding), the stimulus symbol was presented for 25 msec subtending 4 of visual angle to either the left or right of the fixation point. The presentation and randomization of the left-right trial sequence was controlled by computer. Any reaction times (RT) that fell outside the range of rnsec were excluded since very short RT may be due to anticipation and long RT may be the result of lapse of attention (Milner and Lines, 1982). Release of a microswitch attached to the computer terminal served as the response. The time from onset of stimulus to

22 IH'I I release of the button was measured and recorded by the computer as the reaction time. Each test session consisted of 20 practice trials, followed by 6 blocks of 40 trials each. There was a rest period of several minutes between each block. All subjects were asked to wear earphones throughout the experiment. Physiological arousal was produced in some of the subjects by submitting them, through use of the earphones, to a loud (90 db), continuous white noise. Poulton (1979) pointed out that the increase in arousal, which accompanies continuous noise, leads to improvement on simple speed or vigilance tasks. Noise of 90 db during the reaction time experiment should, therefore, produce sufficient physiological arousal to allow any IHTT advantages, derived from increased arousal, to be measured. Twelve of the subjects (early noise group) were submitted to the noise after completion of the second block. Another twelve (late noise group) were submitted to the noise after the fourth block. The final twelve served as a control group and wore the headphones but were not exposed to the noise. IL recorded every ten seconds during the practice and experimental trials using a Inque pulse monitor model PU-701 and the values were averaged for each block. During the interval between

23 IH11 blocks blood pressure was measured with a Copal digital sphygmomanometer UA-271. Results The mean RVF response times were subtracted from the mean LVF times to produce a measure of IHTT per block for each subject. However, as Figure 1 shows, many of the IH I I values calculated in this way were negative, a reversal of the expected results. Most Insert Figure 1 about here subjects produced both negative and positive values, indicating that the times measured were not actually interhemispheric transmission times. The effect of noise on the physiological arousal of the subjects can be seen from Figure 2. Changes Insert Figure 2 about here in pulse rate, calculated by subtracting mean pulse rate/block from the mean pulse rate for the practice trials, declined in the control group as the experiment progressed. The same trend was observed in the late

24 9 noise group until the noise was introduced. At this point the heart rate leveled off. Pulse rate in the early noise group remained relatively constant throughout the experiment and higher than for all other groups. Blood pressure did not change significantly during the experiment. Discussion Due to the invalid measurements of IH1 1', it cannot be determined from this experiment whether or not physiological arousal increases the rate that information is transmitted between hemispheres. As predicted by Poulton, a continuous noise of 90 db did increase the physiological arousal in the experimental subjects. The task required of the subjects was basically a long, eventually monotonous one and, as indicated by the pulse rate of the control subjects, physiological arousal decreased as the experiment proceeded. The late noise experimental group also began to relax until the introduction of the noise after the fourth block of trials. The pulse rate then ceased to decline, remaining instead at the level it was before the noise was activated. The pulse rate of the early noise group did not decline indicating the subjects in this group did not relax, probably attributable to the noise they were listening to.

25 IH1T 10 Figure 3 illustrates the results expected from this study if physiological arousal does increase IHTT. Since the physiological arousal level of the Insert Figure 3 about here control group decreases, the time it takes for a message to cross from one hemisphere to the other may take slightly longer. The late noise group would also show an increased IH I at the beginning since physiological arousal in that group also decreased at the beginning of the experiment. The early noise group would be expected to have fairly constant measurements of IH'1 1 since their level of arousal remained relatively constant throughout the experiment. re vresearch on IHTT using the simple reaction time paradigm produced reliable measurements of around 3 msec (Bashore, 1981). Milner and Lines (1982) also found consistent results measuring IHTT with a simple reaction time paradigm using computers. Since the current study was based on the theory and methodology of these previous studies ( Berlucchi, Crea, DiStefano, and Tassinari, 1977; Berlucchi, Heron, Hyman, Rizzolatti, and Umilta, 1971; DiStefano,

26 11 Morelli, Marzi and Berlucchi, 1980), the measurements of IH I I should have been similar. However, many of the values were negative indicating that for some reason the procedure did not measure IH I I as intended. If negative values were consistently obtained, this would mean that the contralateral response was faster for some reason. However, positive and negative values were evenly mixed. There is no explanation yet as to why the methods designed for use in this study failed to measure IHTT. A possibility is that the stimuli were not displayed at a great enough visual angle to ensure presentation to only one visual field at a time If this is the case, it is an adjustment easily made for replication of the experiment in the future.

27 12 References American Psychological Association (1981). Ethical principles of psychologists. American Psychologist, 36, Bashore, T. (1981). Vocal and manual reaction time estimates of interhemispheric transmission time. Psychological Bulletin, 89, Berlucchi, G., Crea, F., DiStefano, M. and Tassinari, G. (1977). Influence of spatial stimulus response compatibility on reaction time of ipsilateral and contralateral hand to lateralized light stimuli. Journal of Experimental Psychology, 3, Berlucchi, G., Heron, W., Hyman, R., Rizzolatti, and Umilta, C. (1971). Simple reaction times of ipsilateral and contralateral hand LO lateralized visual stimuli. Brain, 94, DiStefano, ivl., Morelli, M., Marzi, C.A. and Berlucchi, G. (1980). Hemispheric control of unilateral and bilateral movements of proximal and distal parts of the arm as inferred from simple reaction time to lateralized light stimuli in man. Experimental Brain Research, 38,

28 IH' I I 13 Milner, A. and Lines, C. (1982). Interhemispheric pathways in simple reaction time to lateralized light flash. Neuropsychologia, 20, Poulton,C. (1979). Composite model for human performance in continuous noise. Psychological Review, 86, Segalowitz, S.J. (1983). Two sides of the brain. New Jersey: Prentice- Hall.

29 IH'I I 14 Figure Caption Figure 1. Mean IHTT measurements per block of trials. Figure 2. Mean changes in pulse rate per block of trials. Figure 3. Diagram of expected IH 1 1 measurements.