A preliminary attempt is made to analyze the intraspecihc aggressive behavior of mammals in terms of specific neural circuitry. The results of stimulation, lesion, and recording studies of aggressive behavior in cats and rats are reviewed and analyzed in terms of three hypothetical motivational systems: offense, defense, and submission. A critical distinction, derived from ethological theory, is made between motivating stimuli that simultaneously activate functional groupings of motor patterning mechanisms, and releasing and directing stimuli that are necessary for the activation (...) of discrete motor patterning mechanisms. It is suggested that motivating stimuli activate pathways that converge upon sets of homogeneous neurons, called motivational mechanisms, whose activity determines the motivational state of the animal. A defense motivational mechanism is hypothesized to be located in the midbrain central gray. In addition to tactile, auditory, and visual inputs from the paleospinothalamic tract, lateral lemniscus, and (perhaps) from the pretectum, it may receive inputs from a major forebrain pathway whose functional significance is not yet understood. A submission motivational mechanism is also thought to be located in the central gray. In addition to inputs for defense, it is thought to receive a necessary input from a "consociate (social familiarity cue) modulator" located in the ventromedial hypothalamus, which can switch behavior from defense to submission. The location of the hypothetical offense motivational mechanism is not known, although the pathways by which it is activated are traced in some detail. (shrink)

The posterior parietal cortex (PPC) is the most likely site where egocentric spatial relationships are represented in the brain. PPC cells receive visual, auditory, somaesthetic, and vestibular sensory inputs; oculomotor, head, limb, and body motor signals; and strong motivational projections from the limbic system. Their discharge increases not only when an animal moves towards a sensory target, but also when it directs its attention to it. PPC lesions have the opposite effect: sensory inattention and neglect. The PPC does not seem (...) to contain a “map” of the location of objects in space but a distributed neural network for transforming one set of sensory vectors into other sensory reference frames or into various motor coordinate systems. Which set of transformation rules is used probably depends on attention, which selectively enhances the synapses needed for making a particular sensory comparison or aiming a particular movement. (shrink)

Engineers use neural networks to control systems too complex for conventional engineering solutions. To examine the behavior of individual hidden units would defeat the purpose of this approach because it would be largely uninterpretable. Yet neurophysiologists spend their careers doing just that! Hidden units contain bits and scraps of signals that yield only arcane hints about network function and no information about how its individual units process signals. Most literature on single-unit recordings attests to this grim fact. On the other (...) hand, knowing a system's function and describing it with elegant mathematics tell one very little about what to expect of interneuronal behavior. Examples of simple networks based on neurophysiology are taken from the oculomotor literature to suggest how single-unit interpretability might decrease with increasing task complexity. It is argued that trying to explain how any real neural network works on a cell-by-cell, reductionist basis is futile and we may have to be content with trying to understand the brain at higher levels of organization. (shrink)