DISSOCIABLE LONG-TERM COGNITIVE DEFICITS AFTER FRONTAL VERSUS SENSORIMOTOR CORTICAL CONTUSIONS

Cognitive deficits are the most enduring and disabling sequelae of hum an traumatic brain injury (TBI), but quantifying the magnitude, durati on, and pattern of cognitive deficits produced by different types of T BI has received little emphasis in preclinical animal models. The obje ctive of the present study was to use a battery of behavioral tests to determine if different impact sites produce different patterns of beh avioral deficits and to determine how long behavioral deficits can be detected after TBI. Prior to surgery, rats were trained to criteria on delayed nonmatching to position, radial arm maze, and rotarod tasks. Rats received sham surgery (controls), midline frontal contusions (fro ntal TBI, 2.25 m/sec impact), or unilateral sensorimotor cortex contus ions (lateral TBI, 3.22 m/sec impact) at 12 months of age and were tes ted throughout the next 12 months. Cognitive deficits were more robust and more enduring than sensorimotor deficits for both lateral TBI and frontal TBI groups. Lateral TBI rats exhibited transient deficits in the forelimb placing and in the rotarod test of motor/ambulatory funct ion, but cognitive deficits were apparent throughout the 12-month post surgery period on tests of spatial learning and memory including: (1)r eacquisition of a working memory version of the radial arm maze 6-7 mo nths post-TBI, (2) performance in water maze probe trials 8 months pos t-TBI, and (3) repeated acquisition of the Morris mater maze 8 and 11 months post-TBI. Frontal TBI rats exhibited a different pattern of def icits, with the most robust deficits in tests of attention/orientation such as: (1) the delayed nonmatching to position task (even with no d elays) 1-11 weeks post-TBI, (2) the repeated acquisition version of th e water maze--especially on the first ''information'' trial 8 months p ost-TBI, (3) a test of sensorimotor neglect or inattention 8.5 months post-TBI, and (4) a DRL20 test of timing and/or sustained attention 11 months after surgery. These results suggest that long-term behavioral deficits can be detected in rodent models of TBI, that cognitive defi cits seem to be more robust than sensorimotor deficits, and that diffe rent TBI impact sites produce dissociable patterns of cognitive defici ts in rats.