Normalization by valence and motivational intensity in the sensorimotor cortices (PMd, M1, and S1)

Our brain’s ability to represent vast amounts of information, such as continuous ranges of reward spanning orders of magnitude, with limited dynamic range neurons, may be possible due to normalization. Recently our group and others have shown that the sensorimotor cortices are sensitive to reward value. Here we ask if psychological affect causes normalization of the sensorimotor cortices by modulating valence and motivational intensity. We had two non-human primates (NHP) subjects (one male bonnet macaque and one female rhesus macaque) make visually cued grip-force movements while simultaneously cueing the level of possible reward if successful, or timeout punishment, if unsuccessful. We recorded simultaneously from 96 electrodes in each the following: caudal somatosensory, rostral motor, and dorsal premotor cortices (cS1, rM1, PMd). We utilized several normalization models for valence and motivational intensity in all three regions. We found three types of divisive normalized relationships between neural activity and the representation of valence and motivation, linear, sigmodal, and hyperbolic. The hyperbolic relationships resemble receptive fields in psychological affect space, where a unit is susceptible to a small range of the valence/motivational space. We found that these cortical regions have both strong valence and motivational intensity representations.

Normalization by Valence and Motivational Intensity in the Primary Sensorimotor Cortices (PMd, M1 and S1)

Our brain’s ability to represent vast amounts of information, such as continuous ranges of reward spanning orders of magnitude, with limited dynamic range neurons, may be possible due to normalization. Recently our group and others have shown that the sensorimotor cortices are sensitive to reward value. In order to determine if normalization plays a role in the sensorimotor cortices when considering non-sensorimotor variables, such as valence and motivational intensity, we had two non-human primate (NHP) subjects (one male bonnet macaque and one female rhesus macaque) make cued grip-force movements while simultaneously cueing the level of possible reward if successful, or time-out punishment if unsuccessful. We recorded simultaneously from 96 electrodes in each the somatosensory, motor and dorsal premotor cortices (S1, M1, PMd). We utilized several normalization models for valence, and motivational intensity in all three regions. We found three types of divisive normalized relationships between neural activity and the representation of reward and punishment, linear, sigmodal and hyperbolic. The hyperbolic relationships resemble receptive fields in psychological affect space, where a unit is particularly sensitive to a small range of the valence/motivational space. We found that these cortical regions have both strong valence and motivational intensity representations.Significance StatementBrain machine interfaces (BMIs) are likely to make their way into the clinical setting in the future. Increasing stability of brain derived control of such BMI systems is one essential aspect towards user acceptance, and stability must be maintained no matter the emotional state of the user. However, it is well known that we move faster for rewards of higher magnitude, indicating that emotions influence the motor control system, where BMI control signals come from. Here we report widespread affective modulation of the sensorimotor regions (PMd, PMv, M1 and S1) by cued levels of possible reward if successful and time-out punishment if unsuccessful in non-human primates, and that affect divisively normalizes these regions activity.

Are interspecific associations of primates in the Western Ghats a matter of chance? A case study of the lion-tailed macaque

When animals or groups of animals in their wild habitats come close to each other within a defined distance, it is termed as an association. Observing two groups of the lion-tailed macaque at Nelliyampathy and Andiparai forests of the Western Ghats of India, we asked whether the lion-tailed macaque associations with the sympatric Nilgiri langur and bonnet macaque were by chance or had any biological significance. Employing ‘all occurrences’ sampling, we recorded an association if a group of another primate species came within 30 m of the focal group of the lion-tailed macaque. Date, time, associating species, activity of the study species and of the associating species, type of interaction, aggressor and the recipient, species displaced and duration of the association were recorded. We used the Waser gas model to calculate the expected frequency and duration of associations and compared them with the observed associations. The lion-tailed macaque spent less time in associations than expected. The lion-tailed macaque and the Nilgiri langur initiated associations less often, and remained in association for less time, than expected by chance. Whereas the expected and observed initiation of associations between the lion-tailed macaque and the Nilgiri langur in Nelliyampathy was significantly different (expected rate = 153; observed rate = 64), in Andiparai, it was not (expected rate = 55.5; observed rate = 61). The expected and observed association duration was significantly different in Nelliyampathy (expected duration = 54 min; observed duration = 15 min) and Andiparai (expected duration = 48 min; observed duration = 19 min). In contrast, we detected few differences between observed and expected association frequency for the lion-tailed macaque and the bonnet macaque. Aggressive interactions were common in areas where density of the Nilgiri langur groups was high. This is the first study on Asian primates using the ideal gas approach to show that primates do not form active associations with each other.