Vernon Mountcastle - US grants

The first objective of this program of research is to discover the dynamic operations of the cerebral neocortex; i.e., how any small region of the cortex operates upon its several inputs to produce its different and divergent outputs, and the meaning for function of its columnar and laminar organization. The second objective is to study these local processing operations simultaneously in several cortical areas that are linked to each other and to other cerebral structures in serial and parallel arrays that constitute distributed systems; we seek to understand the distributed function. Studies will be made in waking, behaving monkeys trained to emit behavioral acts particularly related to or controlled by the cortical areas and systems to be studied. Our strategy is to develop further and to apply experimentally methods for the chronic implantation within the cortex of several and ultimately many microelectrodes for the observation simultaneously of the activity of several and ultimately many cortical neurons. This will allow studies of the processing within cortical networks, the ensemble properties of significant samples of populations of cortical cells, and of different local cortical areas in distributed systems. These techniques and the accompanying methods for data analysis and synthesis will be used in four different investigations: (1) the neuronal operations within the motor and premotor cortex in the initiation and control of aimed movements of the arm and hand; (2) the distributed neuronal processing mechanisms in the somesthetic cortex during the detection of and discrimination between textural surfaces presented to the hand; (3) the dynamic processing operations in the somesthetic cortex during the detection of and discrimination between mechanical sinusoids of different amplitudes and frequencies, with particular reference to how processing differs in areas 3b, 1, 2, and 5, and the columnar, laminar, and distributed system aspects of that processing; and, (4) the intrinsinc dynamic operations of the visual cortex related to stereopsis and depth perception. These studies of different cortical areas and different cerebral systems are strongly linked together by common themes: the intrinsic and dynamic operations within the neocortex, the functional meaning of its columnar and laminar organization, and their relation to sensory and motor events and to certain aspects of the higher functions of the brain.

Cerebral Cortical Mechanisms in Somesthesis. The long-term objective of this research is to discover the intrinsic operating mechanisms of the primate cerebral cortex, particularly those leading to sensation and perception, and to sensory-motor trans- formations. Experiments will be made in waking monkeys as they execute tasks in the somesthetic mode of flutter-vibration, detecting and discriminating between mechanical sinusoids of differing frequencies and amplitudes delivered to the glabrous skin of their hands. The electrical signs of the activity of cortical neurons will be recorded with multiple microelectrodes (n = 7), both by acute insertion in successive daily experiments and after chronic implantation. The first specific aim is to record simultaneously the activity of neurons in the different layers of the primary somatic sensory area 3b of the postcentral gyrus, to discover what transforms are imposed by the intra-columnar proces- sing chains upon the evoked thalamocortical input, and how that transformation may differ along chains leading to different output projection lines; e.g., those that originate in the supra- and infra-granular layers. The second specific aim is to record simultaneously in different layers of areas 1, 2, and 5, to discover how the primary transformations of the dynamically driven cortical activity is further modified along the multistaged cortical system leading from primary sensory to homotypical cortical areas and, it is thought, to sensation and perception. The third specific aim is to study the trans-callosal sensory-motor transform in animals trained to make differential motor responses with one hand after making sen- sory discriminations between stimuli delivered to the other hand. Multiple microelectrode recordings will be made in areas 2, 5 and 4 of the hemisphere ipsilateral to the hand receiving sensory input, and contralateral to the hand making differential motor responses. The fourth specific aim is to study the primary sensory areas, in the manner described above, after chronic implantation of many microelectrodes, to discover what changes occur during long periods of daily sensory training, and whether the spatial, modality, or dynamic response characteristics of cortical neurons can be modified by changes in sensory experience.