John R. Hauser.

Michael A. Cusumano. / Includes bibliographical references (p. 20).

Marc H. Meyer, James M. Utterback. / Includes bibliographical references (p. 15-18).

Varghese P. George, Thomas J. Allen. / Includes bibliographical references (p. 14-17).

Thomas W. Malone ... [et al.]. / "May, 1993." / Includes bibliographical references (p. 18-20). / Supported by the Digital Equipment Corporation. Supported by the National Science Foundation. IRI-8903034

James M. Utterback, Fernando F. Suárez. / "December 1992, Revised July 1993." / Includes bibliographical references (p. 45-52). / Supported by the International Center for Research on the Management of Technology at the MIT School of Management.

Evaluating the efficacy of neuroprotective drugs in rat models of focal cerebral ischemia has involved histological and behavioural batteries to examine pathology and sensorimotor function. However, the behavioural tests used provide little insight into the nature of the neurological impairments. In an effort to gain further insight into the behavioural impairment following ischemic lesions, a battery of tasks were used. The tasks included tests of sensorimotor, motor (paw use), motivation, sensory and attentional function. The use of the potent vasoconstrictor endothelin-1 has allowed cerebral arteries to be occluded. This can be used to occlude the MCA (which is a common target of ischemia research), as well as other arteries, such as the ACA. Typically quantitative volumetric analysis has used nissl stains to assess lesion extent. However, alternative markers of tissue dysfunction are available including GFAP to assess the astroglial response to ischemia. Consequently cresyl violet and GFAP were compared along with different methods for calculating lesion volume. The boundaries of the lesion identified using the two stains corresponded closely providing care was taken when calculating lesion volume to avoid distortion from histological procedures and edema. Following MCA occlusion the rats displayed unilateral somatosensory and motor deficits, however there was no evidence of attentional dysfunction. Performance in the covert orienting task was compared with striatal dopamine depletion and with a posterior parietal cortical lesion. Neither of these manipulations resulted in deficits of covert orienting. Furthermore, the behavioural consequences of ACA occlusion were studied in two experiments using reaction time tasks designed to dissociate response impairments from dysfunction of motivation and attention. The ACA ischemic damage did not disrupt motivation or attention, however, the results were consistent with an impairment in selecting and initiating responses.

The study of pattern classes is the study of the involvement order on finite permutations. This order can be traced back to the work of Knuth. In recent years the area has attracted the attention of many combinatoralists and there have been many structural and enumerative developments. We consider permutations classes defined in three different ways and demonstrate that asking the same fixed questions in each case motivates a different view of involvement. Token passing networks encourage us to consider permutations as sequences of integers; grid classes encourage us to consider them as point sets; picture classes, which are developed for the first time in this thesis, encourage a purely geometrical approach. As we journey through each area we present several new results. We begin by studying the basic definitions of a permutation. This is followed by a discussion of the questions one would wish to ask of permutation classes. We concentrate on four particular areas: partial well order, finite basis, atomicity and enumeration. Our third chapter asks these questions of token passing networks; we also develop the concept of completeness and show that it is decidable whether or not a particular network is complete. Next we move onto grid classes, our analysis using generic sets yields an algorithm for determining when a grid class is atomic; we also present a new and elegant proof which demonstrates that certain grid classes are partially well ordered. The final chapter comprises the development and analysis of picture classes. We completely classify and enumerate those permutations which can be drawn from a circle, those which can be drawn from an X and those which can be drawn from some convex polygon. We exhibit the first uncountable set of closed classes to be found in a natural setting; each class is drawn from three parallel lines. We present a permutation version of the famous `happy ending' problem of Erdös and Szekeres. We conclude with a discussion of permutation classes in higher dimensional space.

Abbie Griffin, John R. Hauser. / "October 1991; revised February 1992." / Includes bibliographical references (p. 43-50).

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