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 persons 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
• Alzheimers 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
Darmasios 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
Libets 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 patients 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
Libets 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 brains 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