cognition, brain and consciousness: an introduction to cognitive neuroscience

Cognition, Brain and Consciousness: An Introduction to Cognitive NeuroscienceEdited by Bernard J. Baars and Nicole M. Gage2007 Academic Press

Chapter 9 Learning and Memory

“What sort of life (if any), what sort of world, what sort of self, can be preserved in a man who has lost the greater part of his memory and, with this, his past, and his moorings in time.”

Oliver Sacks, 1995


Chapter Outline1.0 Introduction

2.0 Amnesia

3.0 Memories are made of this

4.0 Varieties of memory

5.0 MTL in explicit learning and memory

6.0 Prefrontal cortex, consciousness and working memory

7.0 Retrieval and metacognition

8.0 Other kinds of learning

9.0 Summary


1.0 Introduction

Memory can be defined as a lasting representation that is reflected in thought, experience, or behavior.

Learning is the acquisition of such representations -- involving a wide range of brain areas and activities.

Memory storage is believed to involve widespread synaptic alterations in cortex.


1.0 Introduction

The MTL encodes information across sensory domains such as smell, vision, and touch.

The MTL is a highly interactive crossroads, well-placed for integrating multiple brain inputs, and for coordinating learning and retrieval in many parts of the cortex. It is a ‘hub of hubs’.

Important brain structures in the study of memory are the cortex and the medial temporal lobes (MTL), which contain the two hippocampi and their surrounding tissue.


1.0 Introduction

A functional overview: an example of how MTL is believed to help store and retrieve episodic memories.


1.0 IntroductionThe sight of a coffee cup activates visual cortex up to the level of object perception


1.0 IntroductionMemory storage: MTL coordinates widespread memory traces throughout cortex


1.0 IntroductionWhen the episodic memory -- the sight of the coffee cup -- is cued the following day, MTL is once again involved in retrieving and organizing widespread memory traces


1.0 Introduction

Learning and memory in the functional framework: sensory input goes to working storage, part of working memory, which in turn allows information to be actively maintained and manipulated.


1.0 IntroductionImplicit and explicit memory: explicit learning and retrieval involves conscious knowledge; implicit learning and retrieval involves primed tasks, highly practiced habits, and motor skills.


2.0 Amnesia

HM: the best-studied amnesia patient

HM had MTL in both hemispheres removed surgically in an attempt to relieve his epileptic seizures. The surgery was successful in reducing the seizures, but it had a profound and unexpected impact on his memory. HM could not remember any of the events in his life thereafter -- the people he met, the things he did. Even today, he cannot keep track of his age, and can no longer recognize himself in the mirror because he is unfamiliar with his changed image since the surgery in the 1950’s.

The white arrows show lesions where the MTL was removed.


2.0 Amnesia

The functional framework: the typical loss in organic amnesia


2.0 Amnesia

A summary of amnesia

HM’s form of amnesia is a ‘pure’ one because of the surgical removal of MTL bilaterally. Generally, features of amnesia vary widely depending on the nature and extent of injury. Typical features of amnesia due to bilateral MTL damage:

•Impaired memory but preserved perception, cognition, intelligence and action

•Impaired long-term but not working memory

•Impaired recent but not remote memories

•Impaired explicit but not implicit memory


2.0 Amnesia

Spared functions in amnesia: implicit and procedural learning and memory

Implicit -- or unconscious memories -- are typically spared in amnesia, leading memory researchers to suggest separable brain regions for explicit vs. implicit learning and memory


2.0 Amnesia


A way to investigate implicit and explicit learning was developed by Knowlton and colleagues. The patterns on the cards ‘predict’ either rainy or sunny weather with an 80% probability. Healthy individuals implicitly extract the rules in this weather task before they are aware of them explicitly.


2.0 Amnesia


Amnesia patients perform as well as the controls in the early trials that involve implicit rule extraction, but perform worse in the later trials when explicit rule learning is involved.



Electrically evoked autobiographical memories

For more than 50 years, neurosurgeons have reported that awake patients report vivid, specific conscious recollections during temporal lobe stimulation.

Electrode grids are typically placed on the surface of the temporal lobe and areas are systematically stimulated and the patient’s reported memories are noted.



Long-term potentiation and depression: excitatory and inhibitory memory traces

Most synapses in cortex are excitatory, but a large minority are inhibitory. To encode long-term memory traces in changed synaptic efficiency, these excitatory and inhibitory connections must somehow be made more permanent.



Long-term potentiation and long-term depression: excitatory and inhibitory memory traces

These two processes are thought to occur in long-term potentiation (LTP) for excitatory cells and long-term depression (LTD) for inhibitory cells.

Recording from a cell in the hippocampus showing long lasting (90 minutes) activity in an excitatory cell (center).



Consolidation: from temporary to permanent storage

The steps of learning, binding, consolidating, and remembering an event



Rapid consolidation: synaptic mechanisms

Three overlapping time courses for consolidation proposed by McGaugh



Consolidation: interaction between the medial temporal lobes and cortex

Two kinds of consolidation are through to exist: cellular and systems consolidation. Both are evoked by activation of the MTL and cortex.



Memory is not unitary: the Schacter-Tulving classification of memory types



Episodic and semantic memory: ‘Remembering’ versus ‘knowing’

Remembering autobiographical episodes involves an active reconstruction of the original (conscious) episode



Episodic and semantic memory: ‘Remembering’ versus ‘knowing’

Knowing semantic memories does not require active reconstruction of the original episode, it is assessed by a ‘feeling of knowing’.



Episodic memories may turn into semantic memories over time

A model for how semantic and episodic memories may be related: semantic memories may be the cortical residue of many episodic memories.


5.0 MTL in explicit learning and memory

Divided attention interferes with learning

MTL is necessary for conscious recollection of long-term episodic memories.

Learning works best when you pay attention. Researchers have used ‘dual-task’ paradigms to study the effects of divided attention on learning.

Successful encoding requires a level of attention and presumably consciousness.



Working with memory: the frontal lobe works purposefully with memory

The prefrontal cortex (PFC) plays a critical role in working memory. The macaque monkey has been the primary experimental animal if many studies of working memory.

PFC in monkeys (top) and humans (bottom). The most common division is between upper and lower halves of the PFC, called the dorsolateral prefrontal cortex (DL-PFC, purple shading) and the ventrolateral prefrontal cortex (VL-PFC, green shading).



The delayed-match-to-sample task is widely used in studies investigating the role of the PFC in working memory.

In the classic experiment, a monkey is trained to delay responding to a stimulus (‘sample’, typically a red, blue, or white light). The monkey shows recognition of the stimulus after the delay by correctly pressing the light that matched the sample.

Neurons active during the delay period are shown in red at the bottom of the panel.



Different types of working memory

In his seminal work on working memory, Baddeley proposed that there were differing types of working memory: a visuospatial sketchpad for visual inputs and a phonological loop for sound-based inputs.

Neuroimaging studies have shown differing brain areas for visual and verbal working memory processes, with the DL-PFC (D) interacting with Broca’s area (B), a phonological loop (P) and with the frontal eye fields (F).



Combining prefrontal and MTL regions for working memory

One view of visual working memory suggests that the hippocampus may encode working memory items that are novel, the wider MTL may combine them with other modalities, and the inferior temporal (IT) area is involved with high-level visual object representation.



Metacognition is the ability to know our own cognitive functions, and to be able to use that knowledge. Many neurological patients who are severely impaired have no metacognitive insight that anything is wrong.

Healthy individuals use metacognition in memory retrieval. For example, semantic memories may be retrieved by using episodic cues and vice versa



Hemispheric lateralization in retrieval

Do the two hemispheres play differing roles in memory encoding and retrieval?

Tulving and colleagues found that the left hemisphere showed greater activity in episodic learning (encoding), while the right hemisphere showed more activity in episodic retrieval.



Theta rhythms may coordinate memory retrieval: theta oscillations may coordinate MTL and the prefrontal lobe during retrieval


8.0 Other Kinds of LearningMost of what has been presented has been cortical processes for memory, but there are other kinds of memory and brain areas that have not been discussed:


9.0 Summary

The medial temporal lobes (MTL) are crucial to episodic memory in which we retain information about the conscious source of the memory.

Amnesia patients with bilateral MTL damage are unable to remember specific past episodes, or to learn new ones -- however, implicit learning and memory may be spared in these patients.

Working memory can be decomposed into visual and verbal processes.

A complete conception of human memory requires multiple brain regions: the MTL for explicit episodic memories, the prefrontal cortex for metacognition, maintenance, and use of memory, and sensory regions for perceptual and sensory memories.

cognition, brain and consciousness: an introduction to cognitive neuroscience

Documents

cognitive neuroscienceedited

working memory

episodic memory

important brain structures

multiple brain inputs

introductionthe mtl

study of memory

wide range of brain