Cognitive impairments combined with the fact that anything breathed in through the nose goes directly up the olfactory system and impacts on the hippocampus have led doctors and researchers to hypothesize that MCS may start with chemicals interacting with the hippocampal area of the brain. (1,2,3,4)

MCS sufferers typically report memory problems such as getting lost in familiar surroundings, having to go to extraordinary lengths to remember appointments, or not being able to remember telephone conversations. (5) These are examples of spatial, temporal, and episodic memory, respectively, and are controlled by the hippocampus portion of the brain. (6)

A new study on hippocampal damage sheds light on MCS. The study looks at the two types of cognitive memory: Episodic (which includes spatial and temporal memory) and semantic memory. Semantic memory is non-contextual, fact-based memory associated with the ability to learn and is controlled by the entorhinal, perirhinal and parahippocampal cortices of the brain.(6)

The study examines 3 children who sustained hippocampal damage early in their childhood. The first child was injured at birth, the second at age 4, and the third at age 9. The damage to their hippocampuses severely affected the episodic memory capabilities but left their "semantic memory functions relatively intact." (6)

The children in the study were within the low average to average range for speech, language competence, literacy, and factual knowledge according to the results from the Wechsler Objective Reading Dimensions (WORD) test. Yet on the Rivermead Behavioral Memory Test, designed to measure episodic memory, their scores were extremely low, indicative of severe hippocampal impairment. It should be noted that on the Wechsler Memory Scale (WMS) test, their memory scores were lower than what would have been expected given their WORD scores, but were not classified as severe impairments. However, when a 90-minute delay was imposed on the WMS story recall and 40-minute delay on the WMS design reproduction, all three children did extremely poorly. (6)

The memory problems of the MCS sufferers have more in common with the 9-year old than the children who sustained hippocampal damage before they reached the age of reason. Another parallel is that the hippocampal damage in the eldest child was caused by a "toxic dose of theophyline." While these children's experience parallels MCS in many ways, their memory loss is much more severe. In fact, their memory loss is so profound that even as teenagers and young adults they cannot be left unsupervised, "much less lead lives commensurate with their ages, circumstances, and aspirations."(6) Most of the MCS memory problems appear to be intermittent and dependent upon the chemical exposures.(5)

In reviewing over 140 studies(7) involving chemical sensitivity, no study was found in which the episodic memory or the hippocampus of the chemically injured were ever tested, including the recent studies on Gulf War Syndrome. Yet, episodic memory problems are described as a key feature in MCS and Gulf War Syndrome. Studies dealing with the cognitive impairments of MCS use standard tests, like WORD, that document only semantic [fact-based] memories. The results of these type of tests on MCS sufferers are very similar to those of the children - memory deficits not consistent with verbal scores but no gross abnormalities.(6,8)

Hippocampal involvement in MCS was proposed in two review articles by Dr. Iris R. Bell as early as 1992. And while both articles discuss cognitive impairment documented in earlier MCS studies, neither mentions semantic memory versus episodic memory, and those cognitive tests that are mentioned only measured semantic memory.(3,8)

Also in 1992, Dr. Gunnar Heuser wrote two papers on diagnostic markers for MCS patient health problems that included "abnormal behavior, memory and cognitive problems."(9) All
problems that are known to be controlled by the hippocampus.(4,6) But these papers also fail to discuss tests for documenting cognitive memory problems of any kind, let alone the
differences in the types of cognitive memory.

Besides the Rivermead Behavioral Memory Test, hippocampal impairment may also be
documented with "quantitative magnet resonance techniques, namely, volumetric measurements and T2 relaxometry for the detection of hippocampal abnormalities, and proton magnetic resonance spectroscopy (1H MRS) for the detection of more diffuse temporal-lobe abnormalities. These techniques were selected because of their known sensitivity to temporal-lobe pathology."(6)

The two youngest children showed abnormalities on all 3 tests, while the 9 year old showed
abnormalities on the first two. Her 1H MRS was normal.(6)

With the spatial, temporal, and episodic memory problems experienced by most MCS sufferers, taking a closer look at episodic memory and the hippocampus may lead to documenting memory impairments in MCS that are more than just nominal abnormalities.

References:

1. S.A. Schacker: "A Triune Brain Model of MCS," Out Toxic Times, July 1993. $2 Order No. 0112-SCHA-93-006.

2. G. Kobel; T. Hummel: "Olfactory (Chemosensory) Event-Related Potentials," Toxicological & Industrial Health, 1994; 10(4/5). $2.60 Order No. 0098-KOBA-94-010.

3. I.R. Bell, et al.: "An Olfactory-limbic Model for Multiple Chemical Sensitivity Syndrome: Possible Relationships to Kindling and Affective Spectrum Disorders," Biol. Psychiatry, 1992; Vol. 32. $5.20 Order No. 0112-BELL-92-022.

4. C.S. Miller: N.A. Ashford: "Possible Mechanisms For Multiple chemical Sensitivity: The Limbic System and Others," presented at workshop conducted at the request of the EPA and published by the National Research Council as Multiple Chemical Sensitivity, No. 0112-MILL-92-013.

5. Personal reports sent to CIIN as well as in various newspapers and magazine articles
covering MCS and Gulf War Syndrome.

6. F. Vargha-Khadem, et al: "Differential Effects of Early Hippocampal Pathology on Episodic and Semantic Memory," Science, July 18, 1977, Vol. 277. $.180 order No. 0080-VARG-97-005.

7. These are the studies from CIIN's in-house library, topic headings Multiple Chemical
Sensitivity, Sick Building Syndrome, and Gulf War veterans. A list of these topics are available on request.

8. I.R. Bell: "Neuropsychiatric & Biopsychosocial Mechanisms in Multiple Chemical
Sensitivity," presented at workshop conducted at t the request of the EPA and published by the National Research Council as Multiple Chemical Sensitivity, 1992. $5.00 Order No. 0112-BELL-92-021.

9. G. Heuser: "Editorial: Diagnostic markers in Clinical Immunotoxicology and
Neurotoxicology," Journal of Occupational Medicine and Toxicology, Vol. 1, No. 3, 1992.

10. D. Heuser, et al.: Diagnostic Markers of Multiple chemical Sensitivity in Addendum to
Biologic Markers In Immunotoxicology, National Research Council, 1992. $3.20 Order No. 0112-HEUA-92-025R.

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