Yes, from a neurochemical perspective, there are differences in the brain's activity and chemistry between individuals who predominantly have negative thoughts and those who have positive thoughts. These differences are influenced by various factors, including neurotransmitter levels, brain structure and function, and neural pathways. Here are some key points to consider:

### 1. **Neurotransmitter Levels**
- **Positive Thoughts:** Positive thinking and emotions are often associated with higher levels of neurotransmitters like serotonin, dopamine, and endorphins. These chemicals are linked to feelings of happiness, pleasure, and well-being. For example, dopamine is often referred to as the "reward" neurotransmitter, playing a key role in the brain's reward system and motivation.
- **Negative Thoughts:** Chronic negative thinking and emotions, such as those found in depression and anxiety, are often linked to lower levels of serotonin and dopamine. This imbalance can lead to feelings of sadness, hopelessness, and a lack of pleasure or interest in activities.

### 2. **Brain Structure and Function**
- **Positive Thoughts:** Engaging in positive thinking and maintaining an optimistic outlook can strengthen certain neural pathways and even lead to changes in brain structure, a concept known as neuroplasticity. For instance, regular positive thinking can enhance the function of the prefrontal cortex, associated with higher-order functions like decision-making and focusing attention on positive aspects.
- **Negative Thoughts:** Chronic negative thinking can lead to increased activity in the amygdala, the brain's "fear center," which can make individuals more susceptible to stress and anxiety. Over time, this can also affect the hippocampus, an area involved in memory and learning, potentially leading to a decrease in its volume.

### 3. **Stress Response**
- **Positive Thoughts:** Positive thinking can help moderate the body's stress response, reducing the levels of cortisol, a stress hormone. Lower stress levels can have a protective effect on overall brain health and cognitive functions.
- **Negative Thoughts:** Persistent negative thinking can heighten the stress response, leading to elevated cortisol levels. Chronic stress and high cortisol can impair cognitive function and even lead to structural changes in the brain, such as reduced hippocampal volume.

### 4. **Neural Pathways**
- The brain's neural pathways can be reinforced or weakened over time based on thought patterns, a phenomenon known as "Hebb's law" or "neurons that fire together, wire together." Positive thought patterns can strengthen pathways associated with positive emotions and resilience. Conversely, recurrent negative thoughts can reinforce pathways associated with negative emotions and stress responses.

It's important to note that the relationship between thought patterns and neurochemistry is complex and bidirectional. Not only can habitual thought patterns influence neurochemistry and brain function, but changes in neurochemistry (due to factors like genetics, environment, and lifestyle) can also influence thought patterns and mood. This interplay suggests that interventions aimed at promoting positive thinking, such as cognitive-behavioral therapy (CBT), mindfulness, and lifestyle changes, can potentially lead to beneficial neurochemical and functional changes in the brain.