1. The properties of single cells in striate cortex of the rhesus monkey, representing the visual field 2 degrees -5 degrees from the fovea, were examined quantitatively with stationary and moving stimuli. Three distinct classes of cells were identified: S type, CX type, and T type. 2. S-type cells were defined as those oriented cells which to the optimal direction of movement in their receptive fields exhibited one or more spatially separate subfields within each of which a response was obtained to either a light or dark edge, but not to both. Several different types of S-cells were distinguished: a) S1-type cells for which moving edges revealed a single excitatory area within which a response was elicited by either a light or a dark edge but not by both. Most of these cells were unidirectional. b) S2-type cells for which moving edges revealed two spatially separate response areas, one of which was excited by a light edge and the other by a dark edge. Both regions responded to the same direction of movement. c) S3-type cells which had two response areas, one of which was excited by a stimulus moving in one direction (at right angles to the axis of orientation) and the other, of opposite contrast, which responded in the opposite direction, d) S4-type cells which to one direction of movement showed two spatially separate regions sensitive to a light and dark edge and which in the other direction of movement had only one responsive area (either light or dark). e) Cells which had multiple spatially separate subfields (S5-7 types). 3. CX-type cells were defined as those oriented cells which in their receptive fields exhibited no spatial separation for light- and dark-edge responses; they discharged to both edges in the same direction of movement and in the same spatial area. Flashing stimuli elicited both on and off responses throughout the receptive field. CX-type cells were predominantly of two types: those which were selective for direction of stimulus movement and those which were not. 4. A third class of cells (T-type) were those which were excited by only one sign of contrast change and responded in a sustained fashion even when there was no contour within the receptive field. These cells were poorly or not at all oriented; some of them were selective to wavelength. 5. Quantitative comparisons showed the following differences between S-type and CX-type cells: a) S-type cells had smaller receptive fields than CX-type cells but the populations over-lapped considerably. Receptive-field size was smallest in layer 4c. In all other layers S-type cells had the same size fields. CX-type cells, by contrast, tended to have larger fields in layer 5-6 than 2-3. b) The spatial separation between light and dark response areas was the best criterion for distinguishing S-type and CX-type cells. The distribution of this measure disclosed two populations of cells with relatively limited overlap. c) In layers 2 and 3, both S-type and CX-type cells had low spontaneous activity...

1. Quantitative analyses of orientation specificity and ocular dominance were carried out in striate cortex of the rhesus monkey. 2. Sharpness of orientation selectivity was greater for simple (S type) than for complex (CX type) cells. CX-type cells became more broadly tuned in the deeper cortical layers: S-type cells were equally well tuned throughout the cortex. 3. Sharpness of orientation selectivity for S-type cells was similar at all retinal eccentricities studied (0 degrees - 20 degrees from the fovea):in CX-type cells orientation selectivity decreased slightly with increasing eccentricity. 4. The orientation tuning of binocular cells was similar when mapped separately through each eye. 5. Orientation selectivity and direction selectivity are independent of each other, suggesting that separate neural mechanisms give rise to them. 6. More CX-type cells can be binocularly activated than S-type cells (88% versus 49%). The ocular dominance of S-type cells is similar in all cortical layers: for CX-type cells there is an increase in the number of cells in ocular-dominance category 4 in layers 5 and 6.

The sound of birdsong activates robust gene expression in the caudomedial neostriatum (NCM) of songbirds. To assess the function of this genomic response, we analyzed the temporal and quantitative relationships between electrophysiological activity and gene induction. Single units in zebra finch NCM showed large increases in firing in response to birdsong, whereas simple auditory tones tended to inhibit firing. Most cells showed little selectivity for individual songs based on total number of spikes produced. When a novel song stimulus was repeated, the cells rapidly modulated their firing rates so that the first response to a stimulus was markedly higher than consecutive responses. Even after many repetitions of a particular song, cells continued to fire in response to that stimulus, unlike the complete "habituation" observed previously for genomic activity. The initial modulation of the response to a particular song disappeared, however, once that song was repeated for 200 trials (ϳ34 min). These results indicate a dissociation between gross physiological activity and "immediate early" gene expression: genomic activity occurs only during a subset of electrophysiological responses. We propose a model in which nuclear responses in NCM are modulated by pathways distinct from the primary auditory inputs to NCM. This would account for the changing selectivity of the genomic response and implies an active role for the cell nucleus as an integrating agent in the physiological operation of neural circuits.

1. The response properties of single cells in monkey striate cortex were examined using moving bars, square-wave gratings, and sine-wave gratings. 2. The moving of cells studied were not selective for bar width or for the spatial frequency of square-wave gratings. 3. Most cells responded selectively to the spatial frequency of the sine-wave gratings. 4. The spatial frequency of the sine-wave grating eliciting the optimal response could not be predicted from the organization of the receptive field of each cell as determined by stationary or moving stimuli. 5. The sharpness of spatial-frequency selectivity is only slightly more pronounced in S-type cells than in CX-type cells. 6. S-type and CX-type cells differ significantly in the temporal modulation of their discharges to gratings. S-type cells discharge in sharp bursts to each cycle which traverses the receptive field. CX-type cells discharge in a rather continuous fashion. This measure can be used reliably to classify cells as S or CS type.

The mesocorticolimbic system, consisting, at its core, of the ventral tegmental area, the nucleus accumbens, and medial prefrontal cortex, has historically been investigated primarily for its role in positively motivated behaviors and reinforcement learning, and its dysfunction in addiction, schizophrenia, depression, and other mood disorders. Recently, researchers have undertaken a more comprehensive analysis of this system, including its role in not only reward but also punishment, as well as in both positive and negative reinforcement. This focus has been facilitated by new anatomical, physiological, and behavioral approaches to delineate functional circuits underlying behaviors and to determine how this system flexibly encodes and responds to positive and negative states and events, beyond simple associative learning. This review is a summary of topics covered in a mini-symposium at the 2013 Society for Neuroscience annual meeting. IntroductionThe dopamine neurons in the ventral tegmental area (VTA) and their targets in the nucleus accumbens (NAc) and the medial prefrontal cortex (mPFC) are often considered the nexus of the brain's mesocorticolimbic "reward circuit," although it has long been known that neurons in these brain areas are also influenced by aversive stimuli and events (e.g., Bromberg-Martin et al., 2010). With the advent of new anatomical, physiological, and behavioral approaches, and critical attention to psychological constructs, a more sophisticated understanding is emerging of the role of the mesocorticolimbic system in motivated behavior.One area of current investigation is the delineation of functional heterogeneity and specificity of subcircuits in the VTA (reviewed by Ungless and Grace, 2012;Lammel et al., 2013;. It is now apparent that the dopamine (DA) neurons in the VTA comprise several subpopulations distinguished by their afferent and efferent projections, gene expression profiles, electrophysiological properties, and participation in reward and aversion. Similarly, the GABAergic neurons in the VTA display diversity . Tract-tracing experiments in