The Neurobiology of Consciousness and Evolution of Language

1. The Neurobiology of Consciousness and Evolution of Language • Lecture 14. Functional lateralization of cerebral hemispheres. Both hemispheres are involved in doing everything, but each hemisphere is doing it in a totally different way. • Videos: • Broca’s aphasia: http://www.youtube.com/watch?v=f2IiMEbMnPM • Wernicke’s aphasia: http://www.youtube.com/watch?v=aVhYN7NTIKU • Sudden singing off key is caused by a tumor in the right temporal cortex (right h. homologue to Wernicke’s area): https://globalnews.ca/news/4676996/washington-sings-brain-surgery • The Brain: Teaching Modules. (1997): 5. The Divided Brain (definitely show this short movie to introduce Gazzaniga and corpus callosum resection): http://www.learner.org/vod/vod_window.html?pid=1573 • Jill Bolte Taylor: My stroke of insight (TED talk)http://www.ted.com/talks/jill_bolte_taylor_s_powerful_stroke_of_insight • Stephen Wiltshire draws Tokyo from memory: https://www.youtube.com/watch?v=95L-zmIBGd4 • Lecture plan: • Morphology • Functional asymmetry • Differences in encoding of neuronal ensembles • Evolutionary origins of functional asymmetry • Can mental synthesis be conducted by one hemisphere or by both? • Differences in problem solving between the two hemispheres • Development of functional asymmetry • Quiz 4 at the beginning of next lecture is based on homeworks 9, 10 and 11 • The final presentation is optional. • Grading: if you completed all HW and presentations and your quiz total = 75 or more, your grade is A • If you completed all HW and presentations and your quiz total = 50 to 74, your grade is A- • Please complete class evaluation during the break: bu.campuslabs.com/courseeval

2. 1.1 Morphology: Decussation • The left hemisphere controls most muscles on the right part of the body and receiving information from the right sensory field: sense of touch from the right part of the body, sense of sight from the right visual field, etc. • The right hemisphere controls the left part of the body and is mostly receiving information from the left sensory field.

3. 1.2. Morphology: corpus callosum • Hemispheres are connected by corpus callosum. • The corpus callosum is the largest and most prominent bundle of axonal projections in the brain. • It consists of approximately 200 million axons connecting the left and right cerebral hemispheres.

4. Patient J.W. underwent a staged callosal section in which the posterior half of the callosum was sectioned before the anterior half. • Prior to the surgery, J.W. had no difficulty reading words presented to the left visual field (left panel). • Following posterior callosotomy, he was unable to read these words but could transfer categorical (semantic ) information about them (centre panel). • After complete callosotomy, he was no longer able to transfer any information about the words (right panel).[1]

5. 1.3 Morphology: small asymmetry between hemispheres • Morphologically the left hemisphere and right hemisphere are very similar. The only grey matter difference is in Wernicke’s area. • Recall that cortical minicolumns are ~40 µm wide (i.e. a single neuron wide) vertical columns through the cortical layers of the brain (4mm), comprising the total of about 4mm/40µm=100 neurons. • In humans, the distance between the cortical minicolumns is greater in the Wernicke’s area compared to the homologous region in the other hemisphere. • In chimpanzees and rhesus monkeys the distance between the cortical minicolumns is the same size on both sides of the brain. • This asymmetry indicates greater connectivity of Wernicke’s area in humans.

6. =Latin, curved bundle 1.3 Morphology: small asymmetry between hemispheres • White matter difference in the fiber tract connecting Broca’s area to Wernicke’s area. • This fiber tract, called the arcuate fasciculus, connects the large cortical area in the frontal lobe (including Broca’s area, as well as premotor and motor areas) to the large cortical area in the temporal lobe (including Wernicke’s area). • Arcuate fasciculus is essential for interpretation of syntax (i.e. essential for PFS). • Human-specific changes in the structure of the arcuate fasciculus: in chimpanzees and macaques the temporal lobe projections of the pathway have been found to be much smaller or absent (Rilling JK, 2008). • On the right, some people lack an arcuate fasciculus, in others it is smaller in size, and only in a minority of the population is this fiber bundle of equal size in both hemispheres (Catani et al. 2007).

8. 2. Huge asymmetry in function: 2.1 Language lateralization LEFT HEMISPHERE: • Broca's area and Wernicke's area are located in the left hemisphere in 95% of right-handers, and 70% of left-handers. • Broca’s aphasia: http://www.youtube.com/watch?v=f2IiMEbMnPM • Wernicke’s aphasia: http://www.youtube.com/watch?v=aVhYN7NTIKU • Usually only the left hemisphere can understand syntax and spatial prepositions. RIGHT HEMISPHERE: What is the role of the right homologues of the Broca's and Wernicke's areas? • They control and interpret non-verbal communication such as facial expression, gesticulation, modulation of speech rhythm, melody, emphasis, and intonation of speech (prosody) (right hemisphere also identifies a speaker). • Damage of the right hemisphere homologue of Broca’s area  aprosodia. Patients understand the literal meaning of words, but not the rhythms and emotional nuances. • EXAMPLE 1: Sudden singing off key is caused by a tumor in the right temporal cortex: https://globalnews.ca/news/4676996/washington-sings-brain-surgery/ • EXAMPLE 2: R. hemisphere stroke patient D.B. found it difficult to follow conversations, stating, "I understand words, but I'm missing the subtleties, the complex mosaic of meaning that is language" (Beeman, 1993). • EXAMPLE 3: Right hemisphere looks at the big picture of communication and assesses the congruity of the overall expression. Any inconsistencies between how someone holds their body, versus their facial expression, versus their tone of voice, versus the message they are communicating, might indicate either a neurological abnormalities in how someone expresses himself or it might prove to be a telltale sign that the person is not telling the truth. People who have damage in their left hemisphere often cannot create or understand speech. However, they are often genius at being able to determine if someone is telling the truth, thanks for the neurons in their right hemisphere. • EXAMPLE 4: Without the right hemispheres ability to evaluate communication in the context of the bigger picture the left hemisphere tends to interpret everything literally, e.g., “Her head was spinning from all the new information.” Right h. is important in understanding figurative rather than literal meaning of words.

9. 2.2 Split-brain surgery • Left hemisphere receives visual information from the right visual field only. • Right hemisphere receives visual information from the left visual field only.

10. The isolated righthemisphere of most split-brain patients can: • comprehend a lot of spoken words (primarily nouns). • comprehend written words (print-to-image link, but no print-to-sound mapping). • The verbal IQ remains intact. • The capacity for problem-solving (i.e. PFS) is unaffected! • The Brain: Teaching Modules. (1997): 5. The Divided Brain (definitely show this short movie to introduce Gazzaniga and corpus callosum resection): http://www.learner.org/vod/vod_window.html?pid=1573

11. After corpus callosum resection: can right hemisphere, integrate two words presented separately? Flashed “fire” and then “arm” to the right hemisphere. • The left hand drew a rifle rather than an arm on fire. • What about the left hemisphere? • Each hemisphere was able to recognize the meaning of the combined word.

12. Corpus callosum resection • After corpus callosum resection: are the two hemispheres able to communicate with each other? • Flashed “sky” to one hemisphere, “scraper” to the other. • Patient drew a sky atop a comb-like scraper, rather than a tall building. One hemisphere drew what it had seen, then the other drew its word. • Split hemispheres are NOT able to combine the two words. • Sky-scraper • Head-stone

13. 3. Differences between hemispheres in encoding objects • Show Vertumnus by Giuseppe Arcimboldoto a split brain patient • What did the left H. see? • fruits and vegetables, i.e. component details • What did the right H. see? • a person

14. Hypothesis: • The right h. is holistic, encodes a whole scene as one large neuronal ensemble. • The left h. breaks a scene into smaller visual details and encodes smaller visual details as neuronal ensembles. • Experimental observations: • Compare the ability of the two hemispheres to memorize objects with very complex shape? • The right h.=Yes; The left h.=No. • A picture shown of a cow without a tail or a horse with long hanging ears. Compare the ability of the two hemispheres to notice if a small detail is missing in the picture? • The right h.=Yes; The left h.=No. • The left h. doesn’t pay attention to a missing tail in an elephant. It rushes to identify the main feature - the trunk.

15. 3.3 Right h. remembers the forest; Left h. remembers the trees • Predict the result of unilateral brain-damage on ability to memorize visual stimuli consisting of larger forms constructed from smaller forms? • Delis DC, 1986: The right-hemisphere damaged patients made more errors in remembering the larger forms relative to the smaller forms, • whereas the left-hemisphere damaged patients made more errors in remembering the smaller forms relative to the larger forms.

16. 3.4 Stimulate the temporal lobe with an electrode • Predict whether there were more complete memory recollections after stimulation in the left temporal lobe or right temporal lobe? • Penfield’s observations: “Visual illusion and illusion of familiarity was predominantly associated with the non-dominant [right] temporal lobe” VISUAL EXPERIENTIAL RESPONSES TO STIMULATION IN A SINGLE PATIENT Right H. Left H.

17. 3.5 Fusiform face area • Predict the difference between stimulation of the right FFA vs. left FFA? • Right FFA patients report perceiving faces: “That orange part looked like a person ... like a face and a body.... Like a hallucination of the curtains.” …or distortions in face perception (another patient) “You just turned into someone else. Your face metamorphosed. Your nose got saggy and went to the left. You almost looked like somebody I'd seen before but somebody different. That was a trip.”  • Left FFA  patients either perceive nothing or sparkling or flashing lights or traveling blue and white balls, but no change in the character of the perceived face. • Conclusion: the binding neurons for the complete face ensemble seem to be only present in the right hemisphere. The left h. has only small fragments (nose, ears, eye) neuronal ensembles. • But note: Both left and right fusiform gyrus exhibit selective activity when patient is shown faces.

18. 3.6 Predict: a split brain patient is asked to copy a 3-dimentional object => What is the outcome? • It is hard for the left h. to think of a complete scene Sample Right hemisphere copy Left hemisphere copy

19. 4. Evolutionary origins of functional asymmetry • A unit of perception in all animals is an object; in an object all points move together. • In humans, the functions of the left and right hemisphere were likely split: • The human left hemisphere gained the propensity to quickly break objects into details: a tail, an eye, a trunk, and store those elements as neuronal ensembles. • Why was it evolutionarily beneficial?

20. Holistic visual recognition of a partially hidden predator employs amodal completion to fill in missing information and then match the completed image to memory. • To recognize a leopard behind a tree using the holistic method, the visual system must • (1) separate the visual cues, such as a head and a tail, from the background; • (2) complete the body hidden behind the tree in the process of amodal completion; and only after that • (3) match the completed visual percept to targets stored in memory. • It is a longer process!

21. Amodal completion can be observed in birds and other animals. • In humans, holistic visual identification via amodal completion is usually the function of the right hemisphere (Corballis, 1999).

22. The human left hemisphere evolved to quickly break objects into details: a tail, an eye, a trunk, etc. – the smallest meaningful neuronal ensembles. • This identification method helps in matching of all available visual details (an ear or a tail) directly to targets stored in memory, without the intermediate step of amodal completion •  faster and better identification of predators stalking in the savanna.

23. Why is the hemispheric functional asymmetry is so interesting? • Because the new functions of the left hemisphere evolved recently! • The left h. significantly changed during hominin evolution. • The left h. gained the ability to mentally divide objects into fragments: a tail, an eye, a trunk, etc. and store those fragments in separate neuronal ensembles. • Then the left gained the ability to put a word on every fragment (starting from about two million years ago; ) • Finally, the left gained the ability to mentally combine those objects into new objects and scenes prefrontal synthesis (70,000 years ago)

24. Evolutionarily speaking, the left hemisphereis human-like; the right hemisphere is animal-like; the right h. can be used as a proxy for an animal mind to some extent. • WARNING: functions are often mixed between hemispheres. • Just as internal organs (liver, heart, spleen) can be found reversed or mirrored from their normal positions (situsinversus=Lat. Position inverted; 1:10,000)  some cognitive functions can develop in the right hemisphere. • Furthermore even the adult brain retains a lot of plasticity. • As a result of modification, the brain can learn new tricks. • This makes using the right brain as a proxy for animal brain VERY tricky. Discussion can only be conducted “in general” and in any person, general rules can be broken.

25. Downsides of the left h. propensity to analyzeCompetition 1: Rats versus humans • In a probability-guessing experiment, subjects try to guess which of two events will happen next. Each event has a different probability of occurrence (e.g. a red stimulus appears 75% of the time and a green 25% of the time) but the order of occurrence of the events is entirely random. • There are two possible strategies for responding in this task: • Frequency matching: guessing red 75% of the time and guessing green 25% of the time. Since the order of occurrence is entirely random, this strategy could potentially result in a great deal of error. • Maximizing: simply guessing red every time. That ensures an accuracy rate of 75% since red appears 75% of the time. • Wolford (2000) tested the two hemispheres of split-brain patients in this type of probability-guessing paradigm. Can you predict the outcome? • Wolford found that the right hemisphere's accuracy was higher than the left's because the right hemisphere maximized, whereas the left hemisphere used the frequency-matching strategy. • Can you predict the outcome in humans with normal corpus callosum? • Left hemisphere is dominant, so left h. strategy wins and normal humans frequency match. The human's use of this suboptimal strategy has been attributed to a propensity to try to find patterns in sequences of events, even when told the sequences are random. • Animals such as rats and goldfish maximize. The result is that non-human animals perform better than humans in this task. Split-brain rats maximize in both h.

26. Competition 2: Rats versus humans - Detection of the illusory rectangles • Both hemispheres in a split-brain person can judge whether the illusory rectangles are fat or thin when no line is drawn around inducers. • Make a prediction of how this recognition will change after the line around inducers has been drawn? • In humans? • In mice?

27. After the line around inducers has been drawn: • In humans, only the right h. can tell the fat from thin rectangle. • In mice, both hemispheres can tell the fat from thin rectangle. • This suggests that the left hemisphere in humans tends to break visual information into smallest meaningful objects. Once surrounded by a contour, each inducer is perceived by the left hemisphere as a separate object (separate neuronal ensemble).

28. Competition 3: Chimps vs. humans • Matsuzawa short-term memory experiment • The subjects saw nine Arabic numerals displayed on a computer screen (one through nine). • The chimps had been taught to touch the numbers on the screen in the ascending order from one to nine.

29. Masking task (Ayumu, 9 numerals) • When they touched the first number, the other eight numbers turned into white squares (right panel). • Subjects had to remember the position of each number and touch the numbers on the screen in the ascending order from memory. • When the numbers were displayed for about 0.7 seconds, the chimp Ayumu and the college students were both able to correctly remember about 80% of the numbers.

30. The numbers are displayed for just 0.2 second, chimpanzee Ayumu still scores about 80%, while the best humans scored 40%.

31. The numbers are displayed for just 0.2 second, the best humans score about 40%

32. The memory lasted for 10 seconds

33. Global beta rhythm (15Hz): one neuronal ensemble can be attended to by the consciousness every 60ms. • Mental frame 1 (0 ms): the complete visual percept is attended to. • Mental frame 2 (60 ms): the neuronal ensemble representing the first number (1) is separated from the rest on the visual percept and its location is memorized. … • To analyze 5 numbers, it takes 5 X 2 =10 mental frames (10 X 60ms/frame = 600 ms).

34. When the numbers are substituted by squares 210 ms after the start of the test, a human subject can identify no more than two numbers. • The chimpanzee does not rush to analyze the screen but remembers a complete screen; the number identification is performed at a later time (off-line).

35. Can humans learn to suppress the real-time prefrontal analysis? • Yes. Two articles showed that humans can outperform chimpanzees. • But these papers are missing the point: • It is not that humans can suppress the analysis, but it is that normally humans rush into real time analysis and chimpanzees do not. • Possible experiment: show the display to the right hemisphere only  human subjects matching the numbers using only their right hemisphere could improve their performance and achieve a result that is comparable to that of the chimpanzee.

36. A photographic memory may be explained by suppression of the left hemisphere’s analysis • Stephen Wiltshire draws Tokyo from memory: https://www.youtube.com/watch?v=95L-zmIBGd4 • Stephen is likely NOT conducting analysis in real time. All analysis is done off-line when he is drawing the picture.

37. 5. Can prefrontal synthesis be conducted by one hemisphere or by both? - letter-height comparison experiment • In a letter classification task, a split-brain subject, JW, was shown capital letters of the alphabet and asked to classify from memory the lower case forms of letters as medium size or not-medium size*. For example, letters ‘a’ and ‘o’ are medium size and letters ‘h’ and ‘g’ are not-medium size. • Weber and his colleagues have found reaction-time evidence that subjects perform this task by generating an image of the lowercase letter and examining the image to assess letter height. • This imagery task was lateralized by presenting uppercase letters to either side of a fixation point, thereby cuing a single hemisphere with the letter whose lowercase form is to be classified. • The left hemisphere performed at 97% but the right hemisphere performed randomly (it was correct 43% times).

38. 5.2 Predict understanding of syntax in the right h. of patients who understood words in the right h.? • The right hemisphere in patients who understood words in the right h. was not able to understand syntax in the right h. (Gazzaniga et al., 1984). • 5.3 Predict performance on a nonverbal IQ test for the right vs. left hemisphere? • “Left and right intelligence: case studies of Raven's progressive matrices following brain bisection and hemidecortication”, 1981:-Left hemisphere raw score=45 (IQ =85)-Right hemisphere raw score=36 (IQ=76, the threshold for mental synthesis)-both hemispheres raw score=50 (IQ=97)

39. 5.4 The left hemisphere synthesizes a story • Each hemisphere was shown four small pictures, one of which related to a larger picture also presented to that hemisphere. The patient had to choose the most appropriate small picture. • The right h. saw the snowstorm and correctly picked the shovel using the left hand; • The left h. correctly picked the chicken using the right hand. • Then the patient was asked why the left hand (right hemisphere) was pointing to the shovel? • Because only the left hemisphere retains the ability to talk, the left hemisphere answered. • But because the left hemisphere could not know why the right hemisphere was doing what it was doing, it made up a story about what it could see—namely, the chicken. It said “the right hemisphere chose the shovel to clean out a chicken shed.” • Left hemisphere synthesized a story!

40. 6. Asymmetry in problem solving • Can you predict the differences in problem solving approach used by the two hemispheres? Systematic analytic vs. spontaneous insight? • John Kounios, 2009: “The left hemisphere uses analytic search strategy. It involves systematic evaluation of problem states which lie on different possible paths linking the starting state and the goal state. These intermediate states and paths are computed by deliberate, predominantly conscious, manipulation of problem elements” (==prefrontal synthesis). • 6.1 Recall: patients with damage to their left PFC  greater problems with tasks relying on PFS, such as Tower of London. • 6.2 In normal subjects fMRI shows greater activation of the left PFC during all task relying on PFS. • The right hemisphere primarily uses insight, the sudden awareness of the solution to a problem (i.e., the “Aha!” phenomenon) with little or no conscious access to the processing leading up to that solution.

41. 2016, “Insight solutions are correct more often than analytic solutions”: • 38 college students had to think of a single word that could form a compound phrase with three given words such as: “sauce,” “pine,” “crab”. • The answer is “apple:” applesauce, pineapple, crabapples (=wild apples). • At the completion of a timed trial, subjects were asked to report if they had arrived at their answer by thinking the problem through step by step (analytical problem solving) or if the solution had sprung to mind (insight). • Aha! solutions were correct 94% of the time compared with 78% accuracy for analytical solutions.

42. How does the brain generates ‘Aha!’ insights? • Processing occurs largely outside a person's awareness, it is all or nothing—either a fully formed neuronal ensemble with an answer fires in synchrony and therefore jumps into consciousness or it doesn't: • the sudden awareness of insight solutions to verbal problems corresponds to a burst of high-frequency (gamma-band) oscillatory EEG activity associated with an increase in fMRI signal in the RIGHT anterior superior-temporal gyrus (firing of a neuronal ensemble?). • also EEG and functional MRI scans revealed that just before insight takes place, the occipital cortex momentarily shuts down, or “blinks,” so that the neuronal ensemble can overtake the visual cortex and prevent it from processing sensory information coming from eyes. • Two mechanisms of novel neuronal ensembles formation: Categorically-primed spontaneous imagination: bottom-up spontaneous synchronization of primed neuronal ensembles PFS: top-down synchronization

43. How are neuronal ensembles primed? Posterior cortex: encodes sensory experiences into ensembles of neurons capable of self-activation PFC can recall objects using categorical information. It is likely than PFC can also prime a category of objects without activating them. inanimate   predator can fly  prey  animate Frontal cortex Posterior cortex texture cannot fly  shape color

44. 6.3 ‘Sleep on it’ – insight solutions during REM sleep • Subjects found insights in REM sleep when the lateral PFC is not active. • Wagner, 2004, used a mathematical ‘Number Reduction Task’: subjects analyze an 8-digit string of 1’s, 4’s and 9’s, from left to right: 1 1 4 4 9 4 9 4 • They start by determining the appropriate response to the first two digits in the test sequence, and then use that response, together with the next digit in the test sequence, to produce the next response, and so on. • In determining each response, they use two rules: • (a) If two digits are the same, respond with that digit. Thus, starting from the left, the first two digits are both ‘1’, and hence the response is also ‘1’. • (b) If two digits are different, respond with the remaining digit. Having produced the response ‘1’, this response and the next digit (‘4’) differ, so the next response is ‘the remaining digit’, or ‘9’. • This response and the next digit, ‘4’ also differ (‘9’ and ‘4’) and so the next response is the remaining digit, ‘1’. • The analysis is continued to the end, and the final response, ‘9’ in this case, is the solution to the problem. This final response is then entered as the answer the problem. Response = 1 9 1 4 4 1 9 • At training, subjects completed three blocks of 30 trials each (90 problems). Then, after periods of either waking or sleep, they returned for an additional 10 blocks, or 300 problems. • When retesting occurred after one night of sleep, a subgroup of the subjects solved the task, using this ‘standard’ procedure, 16% faster. By contrast, subjects who did not sleep prior to retesting averaged less than a 6% improvement. • But this is not the beauty of the study. For hidden in the construction of the task is a much simpler way to solve the problem. On every trial, it was arranged that the last three response digits (e.g. ‘4-1-9’) are the mirror image of the preceding three (i.e. ‘9-1-4’). As a result, the second response digit always provides the answer to the problem, and an insightful subject can stop after producing the second response digit. Indeed, subjects who discovered this shortcut subsequently reduced their average solution time by over 70%. And, to the author’s delight, 59% of the subjects who slept for a night between training and retesting discovered the short cut the following morning. By contrast, no more than 25% of subjects in any of four different control groups who did not have a night’s sleep had this insight. Thus, ‘sleeping on the problem’ in this case more than doubled the likelihood of solving it. • 1. subjects were not informed that there was a simpler method of solving the problem. So unlike the classic image of sleeping on a problem, subjects did not go to bed knowing there was a problem to solve. • 2. few if any subjects awoke with awareness of the short cut, as one often wakes up with the solution to a problem, or a decision about a future action, clear in one’s mind. Instead, subjects only discovered and implemented the shortcut after an additional 135 trials (on average). • 3. subjects who benefited from sleeping by subsequently finding the shortcut did not show the initial 16% increase in speed. This would suggesting that the sleeping brain can only process the information initially learned one way or the other, either to enhance speed (a simple strengthening of the acquired skill) or to investigate the possibility of alternative solutions (a search for new, creative associations).

45. PFC Puppeteer Puppets in the posterior cortex • Left h. (but not right h.) is capable of Prefrontal Synthesis •  the frontoposterior network is expected to be synchronous only in respect to the left hemisphere PrefrontalSynthesis Synchronization

46. Jill Bolte Taylor • On December 10, 1996, Bolte Taylor woke up to discover that she was experiencing a stroke. The cause proved to be bleeding in the left hemisphere. An abnormal congenital connection between an artery and a vein called anarteriovenous malformation (AVM). • Three weeks later, on December 27, 1996, she underwent major brain surgery at Massachusetts General Hospital (MGH) to remove a golf ball-sized clot that was placing pressure on the language centers in the left hemisphere of her brain. • My stroke of insight (TED talk):http://www.ted.com/talks/jill_bolte_taylor_s_powerful_stroke_of_insight • Jill was experiencing distortions of neuronal ensembles encoding her hands. • Jill was not able to identify her own business card without the left hemisphere == no access to the neuronal ensemble of the business card. • Jill also did not recognize the meaning of Arabic numbers without the left hemisphere  Arabic number neuronal ensembles and their meaning is stored in the left h. • But Jill was able to match Arabic number on the card to Arabic numbers on the phone dialing pad using her right h. without understanding the meaning of numbers. • Jill could not remember the last number she dialed (no working memory, PFC was not able to continuously activate the neuronal ensemble encoding the location) • Jill could not speak or understand spoken language without her left hemisphere.

47. 6.4 Conclusions • The left h. significantly changed in hominin evolution. • The left h. gained the propensity to mentally divide objects into fragments (a tail, an eye, a trunk) in real time and to store the fragments (as smallest meaningful objectNEs) for fast matching to sensory stimuli. • Eventually voluntary Prefrontal Analysis: manufacture of stone tools - 3.3 million years ago. • Then the left h. gained the ability to put a word on every object (starting from two million years; reached modern ability 600,000 years ago) • Finally, the left gained the ability to mentally combine those objects into new objects and scenes Prefrontal Synthesis (70,000 years ago)

48. 7. Development of asymmetry in children • Left hemisphere removed early in life (before 5 YOA)  right hemisphere can take over language functions including prefrontal synthesis. • Thus, both hemispheres are capable of acquiring any function. • It is very interesting that only one hemisphere takes on prefrontal synthesis. Why? • It is likely that it is impossible to make all connections synchronous with respect to both the left LPFC and the right LPFC. • A single puppeteer has to be chosen, and connections have to become synchronous in respect to that puppeteer – usually the left lateral PFC.

49. 7.2 Corpus callosum in children • The myelination of the corpus callosum isnot complete until at least the time of puberty (Gbedd JN, 1999; Giedd, JN, 1996).   • As a result, the brain of a young child is similar to that of a split-brain patient: some types of interhemispheric signal transfer are significantly inferior to that in an adult brain. • For example, children have a greater difficulty matching tactile designs between hands than within hands (Hellige, 1993). • In addition, children younger than 10 months are not able to recognize a face shown to only one hemisphere with the use of the other hemisphere, which indicates an inability to transfer information about the face over the corpus callosum (Schonen & Mathivet, 1990).

50. 7.3 Agenesis of corpus callosum • What is the role of corpus callosum in language / PFS functional lateralization process? • Hypothesis: hemispheric lateralization emerges via cross-hemispheric communication through the corpus callosum. • Experiment: measure cortical activity during language processing, speech preparation, and speech execution (verb generation, picture naming) in 25 participants with agenesis of the corpus callosum (AgCC) and 21 matched neurotypical individuals. • Neurotypical controls: strongly lateralized left hemisphere activations for language • Participants with partial AgCC: bilateral hemispheric activations in both auditory or visually driven language tasks • Complete AgCC participants: significantly more right hemisphere activations than controls or than individuals with partial AgCC. • Agenesis of the corpus callosum  reduced laterality (i.e., greater likelihood of bilaterality or right hemisphere dominance) • These findings suggest that the corpus callosum helps drive language lateralization (maybe one hemisphere has to suppress the other h. via corpus callosum)