Sensory Memory and Working Memory

Sensory Memory

• Brief• Iconic/echoic• High capacity• Pre-attentive• Is there a Neural Correlate of Sensory

Memory?

Is there a Neural Correlate of Sensory Memory?

• Stimuli that deviate from a regular sequence cause a change in the ERP/MEG called the mismatch negativity/mismatch field

• MMN/MMF only occurs when stimuli are close together in time

• Thought to reflect an automatic response to detection of difference between current and previous stimuli

Short-Term Memory

• Duration of seconds• Limited capacity• Not pre-attentive

Neuropsychology of STM

Removal of tumor in L. Angular Gyrus

• Patient E.E.• Reduced digit-span• Normal speech,

comprehension• Normal long-term memory• Why is this finding puzzling?

Working Memory

• STM has been replaced by Working Memory model

Working Memory

• STM has been replaced by Working Memory model

• “Transient representations of task relevant information”

• Limited capacity store AND mechanism for working with that information

• Are there brain structures associated with these functions?

Working Memory

• Left Supramarginal Gyrus and left premotor lesions associated with difficulty holding strings of words in mind

• Right parieto-occipital damage associated with visuospatial memory deficits

• Thus these are doubly dissociated

Working Memory and Frontal Cortex

• An important aspect of working memory is maintaining a representation of previous information while it remains relevant to a current goal

• This information may come via sensory systems, or it may be reactivated from a long-term store

Working Memory and Frontal Cortex

• Animal lesion studies reveal that the Lateral Prefrontal cortex is critical for maintaining these “working” representations

Working Memory and Frontal Cortex

• Goldman-Rakic et al. • Spatial working memory is dissociable from

long-term associative memory

Working Memory and Frontal Cortex

• Working Memory Task– Well is baited with food– Target well changes from

trial to trial– Monkey’s view is blocked

for a delay interval– Monkey must indicate the

baited well to get rewarded

– Requires maintained representation of current target location

Working Memory and Frontal Cortex

• Associative Memory Task– Each well is indicated by a

picture– Target is always associated

with the same picture(s)– Monkey’s view is blocked

for a delay interval– Monkey must indicate the

baited well to get reward– Requires recall of cue from

LTM

Working Memory and Frontal Cortex

• Goldman-Rakic et al. • Spatial working memory is dissociated from

long-term memory• Lesions cause deficit in working memory task

but not association task

Working Memory and Frontal Cortex

• Goldman-Rakic et al. • Spatial working memory is dissociable from

recognition memory

Working Memory and Frontal Cortex

• Working Memory Task– 1 of 3 objects is indicated

to the monkey– View is blocked for a delay– 2 of the 3 objects are

presented– Monkey must select the

non-match object– Requires working memory

because no other cues differentiate the two objects

• Recognition Memory Task– Same as Working memory

task except…– After delay, indicated

object is paired with a novel object

– Monkey must select novel object

– Requires recognition memory to differentiate unfamiliar from familiar objects

Working Memory and Human Frontal Cortex?

Working Memory and Human Frontal Cortex

BOLD signal in lateral prefrontal cortex (area 46) is greater for memory task than for colorDiscrimination task