Remembering when

1. Remembering when A. R. Damasio Scientific American 9/2002

2. Body time • In the course of evolution, humans have developed a biological clock set to rhythm of light and dark • This clock is located in hypothalamus

3. Mind time • Mind time has to do with how we experience the passage of time and how we organize chronology

4. How mind time relates to the biological clock of body time? • Does mind time depend on a single timekeeping device? • Does our experiences of duration and temporal order rely on information processing?

5. Time and memory • Damages to brain regions involved in learning and recalling impair the ability to place past events in the correct epoch and sequence • These amnesics lose ability to estimate the passage of time accurately at the scale of hours, months, years, and decades • Their biological clock often remains intact – brief duration lasting a minute or less is O.K.

6. The experience of these patients suggest that the processing of time and certain types of memory share common neural pathways

7. The association between amnesia and time • Hippocampus is important for memory • Temporal lobe (has 2-way communication with hippocampus) • Damages to the hippocampus prevents the creation of new memories

8. Anterograde amnesics • Patients with hippocampus impaired become unable to hold factual memories for longer than one minute

9. Retrograde amnesia • The memories are stored in a distributed manner in parts of the cerebral cortex (including temporal lobe) • When they are destroyed, patients cannot recover long term memories • The memories lost are those that bear a time stamp

10. Episodic memories • Memories with time stamp: memories of unique events that happened in a particular context on a particular occasion • Episodic memories • Memories about a person’s experience • The temporal lobe that surround the hippocampus is critical in the making and recalling of such memories

11. Damages to the temporal lobe cortex – years and even decades of autobiographical memory can be expunged irrevocably • Viral encephalitis • Stroke • Alzheimer’s disease

12. Time stamps • How the brain assigns an event to a specific time and places that event in a chronological sequence? • How an autobiographical time line is established? • This is a mystery!

13. Darmasio’s investigation 3 groups • Damages to temporal lobe • Damages in the basal forebrain • Control group (normal)

14. Results • The amnesic patients are different from the controls • Time stamping and event recall are processes that can be separated • The basal forebrain may be critical in helping to establish the context that allows correct time stamping

15. Libet’s works • Strange mental time lag • The brain activity occurred a third of a second before the person consciously decided to move his finger • The tingling in the patient’s hand is felt a full half a second after a mild charge to the cortex

16. A time lag exists between the beginning of the neural events leading to consciousness and the moment one actually experiences the consequence of those neural events

17. Libet’s explanation • The brain can institute its own connections on the central processing of events such that, at the microtemporal level, it manages to “antedate” some events so that delayed processes can appear less depayed and differently delayed processes can appear to have similar delays

18. The brain’s ability to edit our visual experiences and to impart a sense of volition after neurons have already acted is an indication of its exquisite sensitivity to time