Semantic memory and brain Lesion studies have shown

Semantic memory and brain • Lesion studies have shown that two primary brain regions are associated with semantic impairment – Left prefrontal cortex – Temporal lobes äSee Martin & Chao (2001), 194 -201, Cognitive Neuroscience for further information

Semantic memory

Semantic memory and brain • Structure of semantic representation – Neurologists have proposed for some time that an object is represented in terms of the sensory and motor attributes that were acquired from experience with the object either by perceiving the object or by acting on the object (e. g. , tool)

Semantic memory and brain • Structure of semantic representation – Thus, an object may be represented by a distributed network of brain regions representing the sensory, motor, and functional attributes for that object – E. g. , colour, form, function, and motor attributes may be represented by those brain regions associated with the perception or motor production

Semantic memory and brain • Structure of semantic representation – It has been shown that asking participants to generate the name of action activated posterior regions of the middle temporal gyrus just anterior to the site active during motion perception

Semantic memory and brain • Structure of semantic representation – Chao and Martin (2000) showed that when participants viewed manipulable objects (e. g. , hammer) a circuit involving the left posterior parietal lobe and the left ventral premotor area became activated, but these areas were not activated when buildings, animals, and faces were presented

Semantic memory and brain • Structure of semantic representation – Many studies have shown that modality-specific regions become active as other types of category knowledge are processed – E. g. , color, shape, and motion properties of category knowledge are processed near the respective brain regions that are involved in perceiving these attributes (see next figure)

Martin & Chao (2001). Current Opinion in Neurobiology (a) Ventral brain regions from occipital to temporal lobes—represent color and shape properties (b) Left lateral areas– motor areas in prefrontal cortex and parietal areas represent manipulation of objects; posterior temporal lobes represent motion properties of objects

Semantic memory and brain • Structure of semantic representation – Weisberg et al. (2007) trained people in the use of novel tools – Behavioral results showed that with extensive training participants became more skilled in their use of novel tools

Semantic memory and brain • Structure of semantic representation – f. MRI scanning -- participants matched pictures of novel tools before and after training – f. MRI findings showed that after training similar brain regions were activated with novel tools that previous research studies have shown are activated with familiar tools

Semantic memory and brain • Structure of semantic representation – Regions of activation were äMiddle temporal gyrus – motion of object äInferior parietal sulcus and premotor area of PFC – tool manipulation äFusiform gyrus (ventral temporal lobe) – appearance of object

Semantic memory and brain • Conclusions – Functional experience with novel objects changed their brain representation – Novel brain region activation similar to that observed with familiar tools – Findings suggest there is a specialized circuitry for learning about the specific sensory and motorrelated properties of objects – This circuitry was activated when perceiving an object; suggests that one function of this circuitry is object perception

Semantic memory and brain • Conclusions – Further research needed to determine what aspects of experience (training) is required to acquire tool-like object representation (e. g. , observation)

Alzheimer’s disease • Alzheimer’s disease – cortical, progressive dementia – disease is associated with the development of neuro-fibrillary tangles and plaques

Alzheimer’s disease • deficit in two or more areas of cognition, at least one of which is memory • interferes with social or occupational functioning • decline from premorbid level • gradually progressive course • rule out other causes

Alzheimer’s disease • Alzheimer’s disease – three types of memory problems äepisodic memory impaired (e. g. , free recall) äexecutive function (WM of Baddeley appears to be affected) äsemantic memory is also impaired – note: pure amnesics do not have the latter two impairments

Alzheimer’s disease • AD – semantic memory ä system for storing, organizing, and manipulating information pertaining to the meaning of words, concepts, and their associations äconceptualized as a broadly distributed network äenables judgments about the properties and functions of items

Alzheimer’s disease • naming and word generation to semantic cues both require semantic memory, both impaired in AD • Explanations: – degradation of the semantic network? – loss of access to preserved concepts? – both?

Putting it together: Component process model of memory • General assumptions of model – Moscovitch believes that memory is not unitary but depends upon the operation of different independent components – this model distinguishes between modules and central systems

Component process model of memory • General assumptions of model – this model postulates that the same modules mediate implicit domain-specific perceptual tests of knowledge and perceptual repetition priming tests äe. g. , prosopagnosics who respond differentially to familiar versus unfamiliar faces on implicit tests show normal repetition priming effects äe. g. , dyslexics who have an intact word-form system show preserved repetition priming effects

Component process model of memory • Overview of model – 4 components – nonfrontal neocortical component made up of perceptual and semantic modules that mediate performance on item-specific implicit memory tests – basal-ganglia component that mediates performance on sensorimotor tests of memory

Component process model of memory • Overview of model – 4 components ämedial-temporal/hippocampal component that mediates explicit memory tests that are cue/dependent or associative äcentral-system frontal-lobe component that “works with memory” and mediates performance on strategic explicit tests

Component process model of memory • Modules and central systems – modules are computational devices that have propositional content and specify three criteria: ädomain specificity äinformation encapsulation äshallow output

Component process model of memory – domain specificity äinformation that a module processes is restricted äimplies that it should be possible to damage this system selectively both functionally and neuroanatomically

Component process model of memory – information encapsulation äprocessing operations of the system are not accessible to higher level functions äit is difficult for higher level functions to modify the processing by the system äimplies that it should be possible for modular functions to process information effectively even when there is general intellectual decline (e. g. , AD)

Component process model of memory – shallow output äoutput has no meaning other than that assigned to it äe. g. , a person with an associative agnosia is quite capable of drawing a viewed object, but cannot name the object, describe its function etc. äSirigu (1991) reported a patient FB with an associative agnosia could appropriately manipulate unidentified objects whose function could not be described

Component process model of memory • Examples of modules – word form recognition system – face-recognition system – phonological-word-form system

Component process model of memory – Central systems äcentral systems integrate information from different dissimilar domains äthe processing carried out by central systems can be influenced by other processes äthe information may be accessible to consciousness äthe output of central systems is meaningful

Component process model of memory • Moscovitch next classifies memory tests using the conceptual framework just presented – caveat -- no test is process pure (Jacoby, 1991)

Component process model of memory • Implicit tests – item specific: perceptual, conceptual – procedural: sensorimotor, ordered/rule-based • Explicit tests – Associative – Strategic

Component process model of memory • Implicit tests: item specific, perceptual äe. g. , identification of fragmented words or pictures – hypothesized process äwhen stimulus presented, it is processed by cortical presemantic modules that transform the stimulus into presemantic structural representation äthis output is then delivered to central system structures for semantic interpretation

Component process model of memory • Implicit tests: item specific, perceptual – the modules that processed the stimulus and the central structures that interpreted the stimulus are modified by the stimulus leaving a perceptual and semantic record – reactivation of this record is the basis of perceptual and conceptual priming effects respectively

Component process model of memory • Implicit tests: item specific, perceptual – anatomical localization – perceptual modules are in the posterior neocortex – evidence (negative) äamnesics show normal perceptual priming ädamage is in the medial temporal lobes and related structures in the diencephalon

Component process model of memory • Implicit tests: item specific, perceptual – evidence (positive) äapperceptive versus associative agnosics äapperceptive agnosics: have relatively intact sensory processes (e. g. , colour, acuity, motion) ähowever, they cannot form a percept of the object äfor example, they are unable to recognize, copy, or match simple shapes

Component process model of memory • Implicit tests: item specific, perceptual – evidence (positive) äapperceptive versus associative visual agnosics äassociative agnosics can copy, recognize, and match objects, but are unable to recognize the identity of an object äapperceptive agnosics tend to have damage in the bilateral regions of the occipital lobes äassociative agnosics tend to have damage in the ventral regions in the anterior temporal lobes

Component process model of memory • Conceptual repetition effects and semantic records – in conceptual repetition tests, the target item is not repeated at test – the target is elicited by a semantic cue (e. g. , a related word or question) äe. g. , generate exemplars of category cues

Component process model of memory • Conceptual repetition effects and semantic records äthis model postulates that conceptual repetition effects are mediated by central systems, which interpret the output from a perceptual module, and store a semantic record of their activity ämodel predicts that modality and format should not affect conceptual repetition effects, but that levels of processing should äthese predictions have been confirmed

Component process model of memory • Conceptual repetition effects and semantic records äConceptual repetition effects have been reported in individuals with amnesia

Component process model of memory • The hippocampal component: A module for episodic, associative memory – conscious recollection of episodes in which the cue is sufficient for retrieval (e. g. , simple recognition and cued recall)

Component process model of memory • The hippocampal component: A module for episodic, associative memory – hippocampal structure consists of a circuit consisting of: hippocampus, parahippocampal gyrus, entorhinal cortex, perirhinal cortex, mammilary bodies, dorsomedial nucleus of the thalamus, the cingulate cortex, and the fornix – amnesia is associated with bilateral damage of these structures

Component process model of memory • The hippocampal component: A module for episodic, associative memory – how it works äthe input modules and central system deliver their output to working memory äthe contents of working memory are accessible to consciousness äthe domain of the hippocampal component is consciously apprehended information (ie the information processed by the hippocampal component)

Component process model of memory • The hippocampal component: A module for episodic, associative memory – how it works ähippocampus binds or integrates the output from the modules and central systems that contributed to the conscious experience äthe bound engram (memory trace) is encoded as a file entry in the hippocampal complex

Component process model of memory • The hippocampal component: A module for episodic, associative memory – how it works äecphory or conscious retrieval occurs when a cue (external or internal) automatically interacts with a memory trace äencoding and retrieval (ecphoric) processes are automatic, obligatory, cognitively impenetrable, and informationally encapsulated because this component is modular

How episodic memory works Conscious Awareness Control systems Encoding/Ecphory

Component process model of memory • Frontal lobes: central systems and strategic explicit tests – frontal lobes critical in memory tests in which extracue strategic factors are critical – e. g. , free recall (esp. categorized FR), memory for temporal order

Component process model of memory • Frontal lobes: central systems and strategic explicit tests – prefrontal cortex is a large heterogeneous structure consisting of several distinct areas, each with its own projections to and from different brain regions, and with its own function äe. g. , dorsolateral versus orbital regions

Component process model of memory • Frontal lobes: central systems and strategic explicit tests – the frontal lobes postulated to play a critical role during encoding by äits selection of memory strategies äby organizing input

Component process model of memory • Frontal lobes: central systems and strategic explicit tests – during retrieval the frontal lobes play a critical role by äorganizing output from hippocampal component ädetermining its temporal order äorganizing mnemonic searches

Component process model of memory • Frontal lobes: central systems and strategic explicit tests äe. g. , What were you doing last Friday? – Frontal lobes änot critical for storage and retention of information (hippocampal) äcritical in those aspects of memory requiring organizational and strategic processing

Component process model of memory • Frontal lobes: central systems and strategic explicit tests – Moscovitch refers to this function as working-withmemory (it is theoretically close to the central executive of Baddeley’s working memory model

Component process model of memory • Procedural implicit tests – two general categories distinguished äsensorimotor and ordered/rule based – sensorimotor äimprovement of motor or sensory skills äe. g. , pursuit rotor, mirror drawing, reading transformed script – ordered/rule based äe. g. , Tower of Hanoi

Component process model of memory • Procedural implicit tests – sensorimotor äbasic assumption of model: acquisition and retention of motor skills result from modification of structures involved in performing the task äperforming a task leaves behind a sensorimotor record äreactivation of a sensorimotor record accounts for performance on implicit tests of memory

Component process model of memory • Procedural implicit tests – sensorimotor äthese assumptions have at least two testable implications äfirst, deficits should be observed in people with damage to sensorimotor structures no matter how well preserved their intellect is äpatients with amnesia should have preserved sensorimotor function

Component process model of memory • Procedural implicit tests – sensorimotor ästudies have shown that patients with AD have normal pursuit rotor function (Jacobs, 1999) äpatients with amnesia have normal pursuit rotor äpatients with Huntington’s and Parkinson’s disease have impaired pursuit rotor learning – Rule learning ä see article

Component process model of memory • Implications of model – perceptual priming is a consequence of reactivation of perceptual-input modules is supported by äfinding of modality-specific priming effects äfinding of strong format effects äfinding that levels of processing effects have negligible effects on perceptual tests (recall perceptual-input modules are presemantic)

Component process model of memory • Implications of model – perceptual priming is a consequence of reactivation of perceptual-input modules is supported by äfinding that perceptual priming effects are little affected by dividing attention (recall modules are hypothesized to operate automatically)

Component process model of memory • The hippocampal module: Implications and comparisons with other models – Is hippocampally-based memory spatial, conscious or both? – Nadel has proposed that the hippocampus is specialized for dealing with spatial information – Moscovitch has claimed that the hippocampus binds together any information that is consciously apprehended

Component process model of memory • The hippocampal module: Implications and comparisons with other models – note: Moscovitch uses the term consciousness interchangeably with phenomenological awareness – ie the individual is aware of having experienced a stimulus previously – Moscovitch argues that the memory trace includes the contents of consciousness as well as the elements that make experience conscious

Component process model of memory – Conscious recollection, thus is a property of the memory trace – Cognitive resources: differential effects on central frontal systems and hippocampal systems äMoscovitch postulated that dividing attention should have differential effects on memory tasks that are mediated by hippocampally versus frontally ästrategy: select tasks known to be affected by frontal damage, and evaluate whether they are impaired by dividing attention