The Neuropsychology of Memory Ch. 11

Outline Case studies Korsakoff’s Amnesia Alzheimer’s Disease Posttraumatic Amnesia Clive Wearing video Theories of consolidation

The Case of R.B. R.B. suffered ischema-produced brain damage during heart-surgery; subsequently, R.B. displayed a pattern of amnesic deficits similar to, although less severe than, that of H.M.

The Case of R.B. After R.B. passed away, a postmortem examination revealed damage to the pyramidal cell layer of the CA1 hippocampal subfield, but no other obvious damage This supported the original hypothesis that H.M.’s deficits were attributable to his hippocampal damage, rather than to damage to other medial-temporal-lobe structures… as we shall see, this may not be the case

Korsakoff’s Amnesia Individuals who chronically consume alcohol develop a pattern of behavioral disorders commonly referred to as Korsakoff’s syndrome In addition to severe anterograde amnesia, Korsakoff patients suffer from a severe retrograde amnesia

Korsakoff’s Amnesia Although their retrograde amnesia is more severe for recent memories, it also affects their memory for events occurring many years before the diagnosis of their case (i.e., for remote events)

Korsakoff’s Amnesia The brain damage associated with Korsakoff’s amnesia is diffuse, although the amnesia is usually attributed to the mediodorsal nuclei of the thalamus

The Case of N.A. N.A. is a patient who was accidentally stabbed in the brain through the right nostril by a friend with a fencing foil; he suffered both retrograde and anterograde amnesia

Korsakoff’s Amnesia A subsequent MRI revealed extensive damage in the mediodorsal thalamic nuclei and the mammillary bodies, providing support that these structures are important in mnemonic function However, despite this evidence, it is unlikely that Korsakoff’s is due to damage to any single brain region

Alzheimer’s Disease Major cause of amnesia; the first symptom is often mild loss of memory Disease is progressive; eventually the dementia becomes severe enough to incapacitate the patient

Alzheimer’s Disease Considerable attention has been focused on predementia Alzheimer’s patients; in addition to both anterograde and retrograde amnesia, these patients often display deficits in short-term memory and some forms of implicit memory (those involving verbal or perceptual material, but not sensorimotor learning)

Posttraumatic Amnesia Blows to the head can lead to a disturbance of consciousness (concussion), a complete loss of consciousness (coma) and posttraumatic amnesia (loss of memory due to a non-penetrating head injury)

Posttraumatic Amnesia Patients with posttraumatic amnesia generally have both anterograde and retrograde amnesia; in general, the anterograde amnesia is longer than the period of coma that produced it, while duration of the coma lasts longer than the period of retrograde amnesia that it produced

Amnesia Clive Wearing video (in class)

Amnesia The retrograde amnesia seen after concussion or coma is typically worse for the most recent memories; this led to the suggestion that older memories are stored in a more permanent form through the process of consolidation

Theories of consolidation Standard consolidation model –Information is encoded in associative cortical areas –Hippocampus integrates info from these distributed modules and fuses features together into coherent memory trace –Successive reactivation of hippocampal-cortical connections (rapid and transient) leads to strengthening of cortico-cortical connections (Hebbian learning; associations that are slow to acquire and long-lasting) –Cortico-cortical eventually become independent from hippocampal-cortical

Theories of consolidation Multiple trace theory (Nadel & Moscovitch) –Memories are encoded in hippocampal-cortical connections –Memory reactivation leads to generation of multiple traces in hippocampus, which are linked to cortical networks –Traces in hippocampus provide spatial and temporal context

Theories of consolidation –Traces in cortex are context-free in nature (they are semantic) –Retrieval of contextually rich episodic memories always depends on hippocampal- cortical networks (these connections never go away as opposed to standard theory) –Retrieval of remote semantic memories is possible in absence of functional hippocampus

Theories of consolidation –Retained memories become progressively more resistant to disruption due to hippocampal damage because each time a similar experience occurs OR The original memory is recalled a new engram (change in brain that stores a memory) is established and linked to the original engram

Brain areas and types of memory Inferotemporal cortex: long-term visual memories Amygdala: emotional significance of event Prefrontal cortex: working memory Cerebellum and striatum: implicit sensorimotor memories

No lecture Thurs… just Exam 4 review