Is There Evidence That Memory Is Separated Into Implicit and Explicit Systems? John Chuckalovcak, Megan Rathburn Q301 Brain and Cognition, Indiana University

Memory is a mystery. What process or processes lay down events and facts in our minds to be recalled at a later date? Why do we sometimes fail to recall? Science still has not found the answer. Recently there has been a growing convergence between cognitive psychology and neuropsychology with focus on memory ret4ention and the study of learning impaired subjects (Tolving). This is the place we pick up the problem. A major theme in current studies is that memory is not a single process but rater it is composed of multiple separate processes (Weiskrantz 1990; Squire, 1992; Schake and Tulving, 1994; Squire and Knowlton, 1994). The separation is between explicit and implicit memory. Explicit memory is declarative and conscious while implicit is non-declarative and thought to be unconscious (Rugg, 1995). Each system is thought to be accessed independent of one another so that they can be retrieved I parallel (Tulving 1994). If in fact two separate systems do exist then it seems logical that two separate brain areas would be working during the activation of the systems. In order to test this theory we devised a direct memory task and used EEG recording techniques. A subject will be given a set of words which are either concrete or abstract to study then at test they will be shown those words again plus some new words of that type. They subject must then make a subjective response about there memory by replying remember, know, or new to the test words. The remember response taps the explicit (conscious) system while the know response keys into the implicit (unconscious) system. We hypothesize the existence of the explicit and implicit systems and that they will be evidenced by spatial distributions of voltage specifically we believe that the remember and know conditions will produce different patterns of electrical response (have different ERPs). We have chosen to use words with high ratings values for concreteness and abstractness. We believe that each will tap into the proposed memory systems in different manors so that if separate systems are not found in one condition they may be in another.

In order to test for a clear and concise physiological difference between the implicit and explicit memory systems, a method needed to be devised that would spark both systems to perform with enough amplitude that decipherable ERP data could be compiled. This system takes the form of a direct- memory test with aspects of subject priming, and essentially uses various types of words as stimuli. The words used for the testing were gathered from a list composed by Dr. Thomas Busey (accessed via Microsoft Excel file at Words.xls). Words.xls) The list made approximately 5,000 words available and each word was given a numerical rating based upon certain factors, such as: concreteness, abstractness, and imagability. In order to try to differentially affect either the implicit or explicit memory systems, two separate types of words were chosen, based upon the ratings they were assigned from the available word pool. Condition One consisted of a total of 300 abstract words, i.e. words that possess an abstract connotation (love, victory, etc.). Of these 300 words, 200 were decided to be target words (given to the subject to study), and the remaining 100 would act as distracter words (not given to the subject during the study session). Condition Two consisted of a total of 300 concrete words, i.e. words that possess a concrete connotation. As in Condition One, 300 of the concrete words were chosen from the available word pool, 200 of which being target words and the remaining 100 serving as distracter words. The word stimuli were collected from the previously mentioned word pool, based upon the effectiveness rating for the appropriate condition. The top-rated 300 words for both Condition One and Condition Two were chosen for stimuli. Of the 300 words in each condition, the 200 with the highest appropriate rating were chosen to act as target words, whereas the remaining 100 would act as distracter stimuli.

Condition 1:Response=Remember : In the color representations of the brain, initial readings at the 200 m.s. time frame show high levels of electrical activity occurring primarily in the dorsal medial portion of the parietal lobe, as well as the rostral portion of the occipital lobe. Subsequent readings occurring at the ms time frame show a localization of processing in the left hemispheric medial and lateral sections of the parietal and frontal lobes. Throughout the readings, high levels of activity continue to occur in the dorsal medial section of the parietal lobe. Condition 2: Response: Remember: Readings taken at 200 m.s. show high amounts of activity occurring in the medial parietal lobe of both hemispheres, as well as moderate amounts of activity occurring in the medial and lateral frontal lobe of the right hemisphere. Readings taken at m.s. illustrate that the highest levels of electrical activity take place in the medial parietal lobe of both hemispheres. Measurements taken at m.s. show a large increase of activity mostly in the left hemisphere of the occipital, parietal, and frontal lobes.

Condition 1:Response=Know: The color representations show an extremely high concentration of electrical activity occurring in the medial parietal and medial occipital lobe of both hemispheres at the 200 m.s. time frame. In addition, high levels of activity take place in the right hemisphere section of the parietal and frontal lobe, as well as in both hemispheres of the pre-frontal cortex. Readings at the 300 m.s. time show a large drop of activity in the lateral frontal and lateral parietal lobe of the right hemisphere, whereas high amounts of activity continue to occur in the prefrontal cortex as well as in the dorsal parietal and rostral occipital lobe. Readings taken at 400 m.s. portray a large increase in activity throughout the majority of portions of the brain, with the exception of a small portion in the frontal lobe of the right hemisphere. Readings taken at 500 m.s. show a centralization of processing in the left hemisphere as well as an almost non-existent level of activity in the lateral portion of right frontal lobe. Activity in the lateral portion of the frontal lobe picks up at m.s. time frame; large increases of activity also occur in the pre-frontal cortex (primarily at 700 m.s.) and the parietal lobe. Condition 2: Response: Know: Readings at 200 m.s. show a great amount of activity at the caudal parietal lobe as well as the rostral occipital lobe. Lower levels of activity can be seen in both the medial and lateral sections of the frontal lobe. Measurements taken at m.s. show a decrease of activity in the medial and lateral sections of the frontal lobe, as well a centralization of the processing to the caudal parietal lobe and the rostral occipital lobe. Readings at 700 m.s. show a fairly large decrease in activity at the caudal parietal lobe and rostral occipital lobe.

Overall: Response=Remember: Readings from m.s. show the majority of processing occurring in the caudal parietal lobe as well as in the entire section of the occipital lobe. At 600 m.s., an increase in activity can be seen in lateral and medial sections of the parietal lobe in the left hemisphere. At 700 m.s., this trend continues with a greater amplitude Overall: Response=Know: At 200 m.s. a great deal of activity is occurring in both hemispheres of the caudal parietal lobe, as well as in many sections of the occipital lobe. From m.s., processing occurs mainly in caudal parietal and rostral occipital lobes. Moderate amounts of activity can also be seen in all sections of the left hemisphere, as well as in the caudal quarter of the right hemisphere.

Based upon the ERP data collected from the memory testing, it can be said that no conclusive physiological difference between explicit and implicit memory systems can be surmised from the available results. The data collected simply did not offer enough spatial or amplitudal differences between the ‘Remember’ and ‘Know’ responses to conclude that there is, in fact a different system for processing implicit memories as opposed to that which processes explicit memories. The major differences between amplitudal and spatial relations of the neural processing seem to occur only when the two conditions are compared. In both the ‘Remember’ and ‘Know’ responses for Condition One, the brain relatively more active than that of the ‘Remember’ and ‘Know’ responses for Condition Two. These differences are possibly due to the fact that a greater amount of processing is required to recall abstract words as opposed to concrete words which showed a more concise ‘streamlined’ effect. This could be due to the fact that no specific memory will personify an abstract word or concept completely, therefore the brain might have to “search” through different areas to assign a meaning to the word.