Den lærende hjernen – syn og hørsel utvikler seg

1. Den lærende hjernen – syn og hørsel utvikler seg Hans M BorchgrevinkNorges forskningsråd NAVkonferanseIKT hjelpemidler til barn født med syns- og hørselshemningOslo 181108

2. How does the brain work? • The brain controls our body and behaviour • Specific parts of the brain are dedicated to control of specific functions

3. How does the brain work? The brain consists of brain cells • aggregated in centres, and • interconnected by nerve fibres in circuits and cortical networks

4. How does the brain work? The cortex is essential for advanced function, • attention • perception • memory • language communication • cognitive function • motor function • executive control and coordination of the brain

5. the cortex

6. How does the brain work? Bodily (vegetative) functions, and reflex actions are largely automatically controlled by pre-programmed underlying sub-cortical structures

7. the cortex sub-cortical structures

8. How does the brain work? • The brain consists of brain cells aggregated in centres and interconnected by nerve fibres in networks and circuits • Chemo-electrical signals(nerve impulses) are transmitted from one cellto the other via the interconnecting nerve fibres, transferred by specific chemical substances: neurotransmitters

9. How does the brain work? • Some signals (neurotransmitters) are excitatory and promote/start transfer of nerve impulse • Other signals (neurotransmitters) are inhibitory and inhibit/stop transfer of nerve impulse

10. The brain cortex • Each cell connects to many others and may receive both excitatory and inhibitory signals • If the ”net” effect of impulses is excitatory and exceeds a certain threshold (minimal level), the signal is transferred • If the ”net” effect of impulses is inhibitory, the signal is stopped

11. How does the brain work? • The brain controls function through a dynamic balance between interconnected excitatory and inhibitory centres and circuits • The ”net” balance of sub-cortical structures is largely excitatory and leads toreflex (impulse) action upon stimulation • The cortex largely inhibits (controls) subcortical impulse actions

12. the cortex sub-cortical structures

13. How does the brain work? • Therefore, organic dysfunction of the cortex characteristically leads to impaired cortical control with impulsive behaviour – e.g. as in ADHD - often accompanied by impairment of advanced functions - e.g. learning disorders

14. Brain localisation The frontal brain controls • attention • planning • control of behaviour • motor function and executive co-ordination of the whole brain

15. Brain localisation • The backmost parts of the brain (parietal, temporal, occipital) control sensation and perception– administered from the frontal brain

16. association cortex speech somatosensory motor start/stop/ integration/attention/executive f I II I II III h III m FRONTAL III read III III II II I visual auditory speech perception I primary cortexII secondary ”III tertiary ” m=mouthh=handf=foot

17. Sensation and perception • The sensory organ transforms environmental stimulation (physical or chemical energy) into nerve impulse signals to the brain • Chains of interconnected cells and fibres transfer the signal to the brain cortex

18. Sensation and perception • In the cortex, analysis by dedicated centres (aggregations of brain cells) and interconnecting fibre circuits and networks leads to perception of the signal • Perception seems to rely on the same place-code principle in all sensory modalities

19. somatosensory motor start/stop/ integration/attention/executive f I II I II III h III association cortex m FRONTAL III read speech III III II II I visual auditory speech perception I primary cortexII secondary ”III tertiary ” m=mouthh=handf=foot

20. Perception - vision • In vision, the image is - projected on to the retina – as in a camera- transferred by parallel optic nerve fibres and - ”projected” on to an area in the visual cortex (I)By converging fibres up through the adjacent cortical networks (II and III) the subject gets an ”overview” perception of the image

21. somatosensory motor start/stop/ integration/attention/executive f I II I II III h III association cortex m FRONTAL III read speech III III II II I visual auditory speech perception I primary cortexII secondary ”III tertiary ” m=mouthh=handf=foot

22. Perception - hearing • In hearing, the sounds are converted to a corresponding place-code in the cochleaEach speech sound is essentially a specific ”chord” of simultaneous tone frequencies- creating wave-tops at frequency-specific positions along the basilar membrane in the cochlea – a place-code much like achord played on a piano keyboard

23. cochlea sound waves nerve impulses to the brain discant 4000 Hz 1000 Hz 125 Hz bass nerve impulses to the brain place code

24. Hearing • The place-coded ”chord” pattern is tranferred by the parallel auditory nerve fibres to the primary auditory cortex (I) • By converging fibres up through the adjacent cortical networks (II and III) the subject gets an ”overview” perception of the sound pattern • The word or sound/chord is recognised by consulting memory from earlier exposure

25. somatosensory motor start/stop/ integration/attention/executive f I II I II III h III association cortex m FRONTAL III read speech III III II II I visual auditory speech perception I primary cortexII secondary ”III tertiary ” m=mouthh=handf=foot

26. Harmonic, consonant chords • When a tone with frequency 250 Hz (~ middle C1) is produced by a vibrating structure, overtones (harmonics) are added at 2x (octave C2) + 3x (fifth G2) + 4x (fourth = double octave C3) + 5x (major third E3) + 6x (minor third = double octave + fifth G3) …. of the given 250 Hz frequency according to physical laws. • Each speech sound consists of the voice frequency plus a pattern of clustered over-tones (formants) – much like a musical chord

27. Harmonic, consonant chords • Playing C3+C4+G4+C5, the upper three tone will coincide with the overtones of the lowest – which is why it is hard to tell how many tones are played • This chord is a con-sonance (”sound together”) • Playing fifth + fifth (C3+G3+D4) is more dissonant, as D4 clashes with the C4 overtone of C3. Thus, combinations of harmonic intervals deviating from the harmonic over-tone pattern do not produce consonance

28. Harmonic, consonant chords • Consonant chords are found in most music cultures – e.g. lithophones in China 1000y BC • Naive rats press more frequently on a lever giving conconance (major third) than a corresponding dissonance • Small infants prefer consonant chords • Variation in terms of degree of deviation from consonance is used as an aesthetic dimension in music

29. Left-right brain specialisation • The left and right brain are largely symmetric mirror images of each other • Certain advanced functions, like verbal language, are controlled by one hemisphere only – or best controlled by one hemisphere

30. Left-right brain specialisation • In right-handers and 2/3 of lefthanders - the left brain is specialised for sequential processing (e.g. speech/language, reading, musical rhythm)- the right brain is specialised for simultaneous, steady-state, ”holistic” pattern analysis (e.g. musical chords, figures, forms, iconic pictures, iconic signs)

31. cortex RIGHT LEFT NON-VERBAL- pitch- chordsVISUAL advanced- figure- form- spatial ICONIC- concrete objects- pictures- gestures- iconic signs- logographicSIMULTANEOUSPATTERNS- e.g. chord, figure • VERBAL- speech- speech perception- rhythm- prosody- read- writePHONOLOGICALhigh demands on- memory span- attention- abstract decodingSEQUENTIALPATTERNS- e.g. rhythm, speech, reading

32. Brain specialisation in musicians • Some professional musicians have by excessive training established musical intervals like over-learned concepts / entities (e.g. a fifth) – engaging also the left brain in the control of tone pitch • Absolute pitch (to sing a note from the score in correct pitch without reference pitch) takes inherited brain potential plus exposure and active training in fixed-pitch environment

33. Melody • Melody is a pattern of varying tone pitch and rhythm which engages both sides of the brain • In stuttering and types of expressive aphasia, the ”start” (excitatory) signal does not reach the threshold (minimum) for starting speech • Simultaneous singing or rhythmic movement creates bilateral brain activation which combined may reach threshold and facilitate speech start and fluency

34. Memory span and music • Memory span is e.g. how many random digits, words or tones that can be immediate repeated in correct order – a ”working memory” (RAM) capacity, not trainable - in adults = 6 or 7 +/- 1 (i.e. normal range 5-8)- in children = age in years to 6y, +/-1 from 5y • Melodic motives must keep within memory span to be perceived and recognised – both in classical (e.g. sonata scheme) and pop music • Children’s songs have short melodic motives

35. Memory storage and retrieval • Memory (learning) requires - presentation / exposure- perception (e.g. within memory span, repeat)- association (coupling) according to semantic, structural and/or situational - the act of storage (librarian)- archives (library)- retrieval by recall (without being shown) or recognition (among shown items, easier)

36. Brain maturation • The infant is born with immature brain cortex • Body functions and reflex actions are automatically controlled by pre-programmed reflex actions in underlying (sub-cortical) structures, which are largely developed at birth

37. the cortex sub-cortical structures

38. Brain maturation • Accordingly, infant behaviour is largely dominated by reflex actions related to fundamental body needs

39. Brain maturation • With increasing age the number of nerve fibre connections between the brain cells is gradually increased and differentiated to a cortical network of increasing density • A dense network has more connections, larger capacity, increased flexibility and thus can handle more complex programmes

40. Brain maturation • Increasing myelinisation (”coating”) of nerve fibres increases conduction velocity(”faster processor”) • Combined, this ”upgrading” enables the brain to control and co-ordinate more complex functions faster and more flexible with increasing age - up to 18 years – (after which deterioration starts, first in co-ordination areas)

41. Early stimulation - critical age • Early infant stimulation gives the most efficient cortical networking.In fact, • adequate sensory stimulation in certain- sensitive periods, and - before a certain critical age,is required to establish the cortical networks needed for successful perception of the sensory signal • Early adequate training is essential

42. Critical age - vision • This is well demonstrated by consequences of early sensory deprivation(=severe lack of sensory stimulation) • Congenital blindness and -deafnessare good examples of sensory deprivation

43. Critical age - vision • Born blind from inborn cataract(opaque lens) not operated by replaced lens before age ~7 years, the subject remains blind regardless of later visual stimulation because the visual cortex fails to develop proper cortical circuits and networks due to lack of stimulation

44. somatosensory motor start/stop/ integration/attention/executive f I II I II III h III association cortex m FRONTAL III read speech III III II II I visual auditory speech perception I primary cortexII secondary ”III tertiary ” m=mouthh=handf=foot

45. Critical age - vision • Operation before age 3 monthsgives normal visual function • Operation between age 3 months and 7 years: the later the operation – the poorer cortical network – and thus the poorer visual function

46. Critical age - hearing • Cochlear implants (CI) have demonstrated a corresponding critical age for hearing: • CI consists of a microphone, a computer that can convert the speech sound, and an electrode with ~20 ”un-isolated areas” along its length • The electrode is operated into the cochlea • Speech sounds are converted to different on-off activation patterns along the electrode • CI thus mimics the place code of speech sounds along the basilar membrane

47. cochlea sound waves nerve impulses to the brain discant 4000 Hz 1000 Hz 125 Hz bass nerve impulses to the brain place code

48. Hearing • The place-coded ”chord” pattern is tranferred by the parallel auditory nerve fibres to the primary auditory cortex (I) • By converging fibres up through the adjacent cortical networks (II and III) the subject gets an ”overview” perception of the sound pattern • The word or sound/chord is recognised by consulting memory from earlier exposure

49. somatosensory motor start/stop/ integration/attention/executive f I II I II III h III association cortex m FRONTAL III read speech III III II II I visual auditory speech perception I primary cortexII secondary ”III tertiary ” m=mouthh=handf=foot

50. Critical age - hearing • Born deaf,CI operation after age ~7 years gives no functional hearing apart from on/off effects because the deprived brain fails to develop adequate cortical auditory net-works at primary (I), secondary (II) and tertiary (III) level • Effects of CI implanted after age ~7 years indicates transient hearing at an earlier age, having left some cortical network