BRAIN RHYTHMS & SLEEP

1. BRAIN RHYTHMS & SLEEP Psychology 2401 Foundations of Biopsychology Alana Rawana 2013

2. RHYTHMIC ACTIVITY • Environment is rhythmic • Brains have evolved a variety of systems for rhythmic control • Mammalian rhythmicity: • Thirst and hunger • States of arousal (alertness) • Hormonal secretion • Respiration • Heart rate • Electrical rhythms of the cortex • THE SLEEP WAKE CYCLE

3. ELECTROENCEPHALOGRAM • EEG: • Classic method of recording brain rhythms • A measurement that enables us to take a generalized look at the activity of the cerebral cortex • Richard Caton (England, 1875) • Electrical recordings from the surface of dog and rabbit brains • Hans Berger (Austria, 1929) • First described the human EEG • Observed differences in EEG activity What are EEG’s used for today?

4. ELECTROENCEPHALOGRAM

5. RECORDING BRAIN WAVES • Method is non-invasive & painless • Wire electrodes are taped to the scalp, along with a conductive paste to lower the resistance • Electrodes are placed on standard positions on the head • Electrodes are connected to banks of amplifiers and recording devices • Small voltage fluctuations are measured between pairs of electrodes

7. RECORDING BRAIN WAVES CONT’D • WHAT GENERATES THE OSCILLATIONS OF AN EEG? • An EEG measures voltages generated by dendritic synaptic excitation of pyramidal cells of the cortex • However, any single neuron does not contribute much to the electrical signals recorded by the EEG • Therefore, an EEG is a reflection of many thousands of neurons firing simultaneously

8. EEG

9. CONSEQUENCES OF SUMMATION • The amplitude of EEG signal strongly depends, in part, on how synchronous the activity of the underlying neurons is. • Synchronous activity: when a group of cells are simultaneously excited and the “mini” individual signals summate to generate one large surface signal • Irregular activity: when a group of cells receives the same amount of excitation but do not respond simultaneously the summation does not amount to much

10. Synchronous activity

11. Magnetocephalography (MEG) • Wherever electrical current flows a magnetic field is generated • Magnetic current detected by an array of 150 sensitive magnetic detectors • MEG vs EEG • What are MEG’s used for today?

12. Magnetocephalography (MEG)

13. EEG RHYTHMS • EEG rhythms vary drastically depending on particular states of behavior or pathology • e.g. level of attentiveness, arousal, sleeping, waking…coma, seizures • EEG rhythms are categorized according to their frequency range…

14. TYPES OF RHYTHMS • Beta rhythms: fastest, greater than 14Hz, signal activated, alert cortex • Alpha rhythms: 8-13Hz, signal awake but quiet and relaxed states • Theta rhythms: 4-7Hz, signal some of the deep sleep states • Delta rhythms: very slow, very large in amplitude, less than 4Hz, hallmark of deep sleep

16. Normal EEG • Alpha & beta waves • Both sides of brain show similar patterns of electrical activity • No abnormal bursts of electrical activity & no slow brain waves • Proper response to photic stimulation

17. Abnormal EEG

18. Abnormal EEG (Cont’d…) • Sudden bursts of electrical activity or sudden slowing of brain waves • Delta waves or too many theta waves in adults who are awake. • a "flat" or "straight-line" EEG

19. EEG Rhythms Cont’d… • Obviously EEG recordings do not allow us to read a persons thoughts, but they do allow us to tell if a person is thinking • frequency: amplitude rhythms are associated with alertness, waking, and dreaming sleep states • frequency: amplitude rhythms are associated with non-dreaming sleep states and pathological states of coma

20. Generation of Synchronous Rhythms • Activity of a large set of neurons produce synchronized oscillations in one of two ways: • They may take cues from central clock (pacemaker) • Share or distribute the timing fcnamong themselves by mutually exciting or inhibiting one another

21. Synchronous Activity – Mammalian Brain • Rhythmic synchronous activity is usually coordinated by a combination of the pacemaker & collective methods • Thalamus • Can generate very rhythmic action potential discharges • How do thalamic neurons oscillate?

22. How do thalamic neurons oscillate?

23. How do thalamic neurons oscillate? (Cont’d…) • Synaptic connections between excitatory and inhibitory thalamic neurons force each individual neuron to conform to the rhythm of the group • Coordinated rhythms passed to cortex

24. Function of Brain Rhythms • Why are there so many rhythms? • Do they serve a purpose? • Obviously there are no satisfactory answers to either of these questions… but there are a few decent hypotheses

25. Functions of Brain Rhythms Cont’d… • “Disconnection Hypothesis”: • Sleep-related rhythms are the brain’s way of disconnecting the cortex from sensory input • AWAKE, sensory information is allowed to the cortex via the thalamus • ASLEEP, the thalamus goes on auto-pilot, the neurons enter a self-regulated state that prevents the relay of sensory input to the cortex

26. Functions of Brain Rhythms Cont’d… • Walter Freeman • Neural rhythms coordinate activity between regions of the NS • Gamma rhythms • Momentarily synchronizing fast oscillations generated by different regions of cortex brain binds neural components into a single perceptual construction • Another plausible reason?

27. Seizures of Epilepsy • Most extreme form of synchronous brain activity • Generalized seizure: involves the entire cortex of both hemispheres • Partial seizure: involves a particular area of the cortex Commonalities between the two? • Epilepsy: a condition defined by repeated seizure experiences • ~ 1% of the American population has epilepsy

28. Seizures and Epilepsy (Cont’d…) • The cause of seizures can sometimes be identified • Examples • Different types of seizures have different underlying mechanisms • Genetic predisposition

29. Convulsants & Anticonvulsants GABA receptor antagonists are very potent convulsants: • Block GABA receptors • Seizure-promoting agents • Common uses? GABA receptor agonists are very potent anticonvulsants: • Suppresses seizures by countering excitability in various ways… • E.g., prolong inhibitory influence of GABA

30. Behavioural Features of Seizures • During more forms of generalized seizures: • All cortical neurons are engaged • Unconscious • Muscles – tonic or clonic activity • John Hughlings Jackson - Partial Seizures

31. Pathological Brain Activity: Seizures & Epilepsy

32. Sleep • We spend about one-third of our lives sleeping • One-quarter of this time is spent dreaming • Sleep is universal among higher vertebrates • Sleep is essential to our lives, like eating and breathing • Prolonged sleep deprivation can devastate proper functioning and in some animals, lead to death

33. Sleep (Cont’d…) • DEFINITION OF SLEEP: • Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment (anesthesia and coma do not count since they are not readily reversible)

34. Rapid Eye Movement Sleep • REM sleep • When EEG looks more awake than asleep • Your body (except eye and respiratory muscles) is immobilized • Dreaming sleep • Non-REM sleep a.k.a., slow-wave sleep • Period of rest • Temperature and energy consumption lowered • Heart rate, respiration, and kidney fcn all slow down • Digestive processes speed up • Brain rests

36. REM AND NON-REM SLEEP • William Dement (Stanford University): REM SLEEP: “An active, hallucinating brain in a paralyzed body” NON-REM SLEEP: “An idling brain in a movable body”

38. ultradian rhythms

39. How are sleep spindles generated?

41. Sleep Related Disorders • Insomnia • Affects at least 20% of population at some time • Example case • One of the most important causes of insomnia seems to be sleeping medication • Sleep Apnea

42. Sleep-Related Disorders (Cont’d…)

43. Why do we sleep? • All birds, reptiles, and mammals appear to sleep • Although only mammals and some birds have REM phases

44. Cool Animal Sleep Facts The Bottlenose Dolphin • Have more reason not to sleep • Live in deep water and must breathe air every minute or so (no napping) • However, they still manage to get as much sleep as humans do • How???

45. Bottlenose Dolphin • They sleep with one cerebral hemisphere at a time! • About 2 hours asleep on one side, then 1 hour awake on both sides, then 2 hours asleep on the other side… • For a grand total of 12 hours a night • Do not seem to have REM sleep

46. Indus River Dolphin

47. Sleep Theories • Theories of restoration vs. theories of adaptation • We sleep to rest and recover • We sleep to keep us out of trouble • Does sleep renew us the same way eating and drinking do?

48. Functions of Dreaming and REM Sleep • Dreams are difficult to study • Modern studies tend to look at REM sleep rather than dreams…REM sleep can be measured objectively • Remember, REM sleep and dreaming are not synonymous • Dreams can occur during non-REM sleep and many peculiar things occur during REM sleep that have nothing to do with dreaming

49. Dreaming and REM sleep (cont’d…) • Do we need to dream? Who knows. • But, we do need REM sleep • If people are deprived of REM sleep for a few days they will experience REM rebound • Sleepers will attempt to enter REM more rapidly and will spend more time in REM proportional to the duration of their deprivation • Studies have found that REM deprivation does not cause any psychological harm during the daytime

50. Dream Theories • Sigmund Freud • Dreams are disguised wish-fulfillment, an unconscious way for us to express our sexual and aggressive fantasies, which are forbidden to us when we are awake • Hobson & McCarley (Harvard University) • More biologically based theories • “activation-synthesis hypothesis” • Dreams are seen as associations and memories of the cortex that are elicited by the random discharges of the pons during REM sleep